1 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 2 <HTML> 3 <HEAD> 4 <TITLE>Lua 5.3 Reference Manual</TITLE> 5 <LINK REL="stylesheet" TYPE="text/css" HREF="lua.css"> 6 <LINK REL="stylesheet" TYPE="text/css" HREF="manual.css"> 7 <META HTTP-EQUIV="content-type" CONTENT="text/html; charset=iso-8859-1"> 8 </HEAD> 9 10 <BODY> 11 12 <H1> 13 <A HREF="http://www.lua.org/"><IMG SRC="logo.gif" ALT="Lua"></A> 14 Lua 5.3 Reference Manual 15 </H1> 16 17 <P> 18 by Roberto Ierusalimschy, Luiz Henrique de Figueiredo, Waldemar Celes 19 20 <P> 21 <SMALL> 22 Copyright © 2015–2018 Lua.org, PUC-Rio. 23 Freely available under the terms of the 24 <a href="http://www.lua.org/license.html">Lua license</a>. 25 </SMALL> 26 27 <DIV CLASS="menubar"> 28 <A HREF="contents.html#contents">contents</A> 29 · 30 <A HREF="contents.html#index">index</A> 31 · 32 <A HREF="http://www.lua.org/manual/">other versions</A> 33 </DIV> 34 35 <!-- ====================================================================== --> 36 <p> 37 38 <!-- $Id: manual.of,v 1.167.1.2 2018/06/26 15:49:07 roberto Exp $ --> 39 40 41 42 43 <h1>1 – <a name="1">Introduction</a></h1> 44 45 <p> 46 Lua is a powerful, efficient, lightweight, embeddable scripting language. 47 It supports procedural programming, 48 object-oriented programming, functional programming, 49 data-driven programming, and data description. 50 51 52 <p> 53 Lua combines simple procedural syntax with powerful data description 54 constructs based on associative arrays and extensible semantics. 55 Lua is dynamically typed, 56 runs by interpreting bytecode with a register-based 57 virtual machine, 58 and has automatic memory management with 59 incremental garbage collection, 60 making it ideal for configuration, scripting, 61 and rapid prototyping. 62 63 64 <p> 65 Lua is implemented as a library, written in <em>clean C</em>, 66 the common subset of Standard C and C++. 67 The Lua distribution includes a host program called <code>lua</code>, 68 which uses the Lua library to offer a complete, 69 standalone Lua interpreter, 70 for interactive or batch use. 71 Lua is intended to be used both as a powerful, lightweight, 72 embeddable scripting language for any program that needs one, 73 and as a powerful but lightweight and efficient stand-alone language. 74 75 76 <p> 77 As an extension language, Lua has no notion of a "main" program: 78 it works <em>embedded</em> in a host client, 79 called the <em>embedding program</em> or simply the <em>host</em>. 80 (Frequently, this host is the stand-alone <code>lua</code> program.) 81 The host program can invoke functions to execute a piece of Lua code, 82 can write and read Lua variables, 83 and can register C functions to be called by Lua code. 84 Through the use of C functions, Lua can be augmented to cope with 85 a wide range of different domains, 86 thus creating customized programming languages sharing a syntactical framework. 87 88 89 <p> 90 Lua is free software, 91 and is provided as usual with no guarantees, 92 as stated in its license. 93 The implementation described in this manual is available 94 at Lua's official web site, <code>www.lua.org</code>. 95 96 97 <p> 98 Like any other reference manual, 99 this document is dry in places. 100 For a discussion of the decisions behind the design of Lua, 101 see the technical papers available at Lua's web site. 102 For a detailed introduction to programming in Lua, 103 see Roberto's book, <em>Programming in Lua</em>. 104 105 106 107 <h1>2 – <a name="2">Basic Concepts</a></h1> 108 109 <p> 110 This section describes the basic concepts of the language. 111 112 113 114 <h2>2.1 – <a name="2.1">Values and Types</a></h2> 115 116 <p> 117 Lua is a <em>dynamically typed language</em>. 118 This means that 119 variables do not have types; only values do. 120 There are no type definitions in the language. 121 All values carry their own type. 122 123 124 <p> 125 All values in Lua are <em>first-class values</em>. 126 This means that all values can be stored in variables, 127 passed as arguments to other functions, and returned as results. 128 129 130 <p> 131 There are eight basic types in Lua: 132 <em>nil</em>, <em>boolean</em>, <em>number</em>, 133 <em>string</em>, <em>function</em>, <em>userdata</em>, 134 <em>thread</em>, and <em>table</em>. 135 The type <em>nil</em> has one single value, <b>nil</b>, 136 whose main property is to be different from any other value; 137 it usually represents the absence of a useful value. 138 The type <em>boolean</em> has two values, <b>false</b> and <b>true</b>. 139 Both <b>nil</b> and <b>false</b> make a condition false; 140 any other value makes it true. 141 The type <em>number</em> represents both 142 integer numbers and real (floating-point) numbers. 143 The type <em>string</em> represents immutable sequences of bytes. 144 145 Lua is 8-bit clean: 146 strings can contain any 8-bit value, 147 including embedded zeros ('<code>\0</code>'). 148 Lua is also encoding-agnostic; 149 it makes no assumptions about the contents of a string. 150 151 152 <p> 153 The type <em>number</em> uses two internal representations, 154 or two subtypes, 155 one called <em>integer</em> and the other called <em>float</em>. 156 Lua has explicit rules about when each representation is used, 157 but it also converts between them automatically as needed (see <a href="#3.4.3">§3.4.3</a>). 158 Therefore, 159 the programmer may choose to mostly ignore the difference 160 between integers and floats 161 or to assume complete control over the representation of each number. 162 Standard Lua uses 64-bit integers and double-precision (64-bit) floats, 163 but you can also compile Lua so that it 164 uses 32-bit integers and/or single-precision (32-bit) floats. 165 The option with 32 bits for both integers and floats 166 is particularly attractive 167 for small machines and embedded systems. 168 (See macro <code>LUA_32BITS</code> in file <code>luaconf.h</code>.) 169 170 171 <p> 172 Lua can call (and manipulate) functions written in Lua and 173 functions written in C (see <a href="#3.4.10">§3.4.10</a>). 174 Both are represented by the type <em>function</em>. 175 176 177 <p> 178 The type <em>userdata</em> is provided to allow arbitrary C data to 179 be stored in Lua variables. 180 A userdata value represents a block of raw memory. 181 There are two kinds of userdata: 182 <em>full userdata</em>, 183 which is an object with a block of memory managed by Lua, 184 and <em>light userdata</em>, 185 which is simply a C pointer value. 186 Userdata has no predefined operations in Lua, 187 except assignment and identity test. 188 By using <em>metatables</em>, 189 the programmer can define operations for full userdata values 190 (see <a href="#2.4">§2.4</a>). 191 Userdata values cannot be created or modified in Lua, 192 only through the C API. 193 This guarantees the integrity of data owned by the host program. 194 195 196 <p> 197 The type <em>thread</em> represents independent threads of execution 198 and it is used to implement coroutines (see <a href="#2.6">§2.6</a>). 199 Lua threads are not related to operating-system threads. 200 Lua supports coroutines on all systems, 201 even those that do not support threads natively. 202 203 204 <p> 205 The type <em>table</em> implements associative arrays, 206 that is, arrays that can have as indices not only numbers, 207 but any Lua value except <b>nil</b> and NaN. 208 (<em>Not a Number</em> is a special value used to represent 209 undefined or unrepresentable numerical results, such as <code>0/0</code>.) 210 Tables can be <em>heterogeneous</em>; 211 that is, they can contain values of all types (except <b>nil</b>). 212 Any key with value <b>nil</b> is not considered part of the table. 213 Conversely, any key that is not part of a table has 214 an associated value <b>nil</b>. 215 216 217 <p> 218 Tables are the sole data-structuring mechanism in Lua; 219 they can be used to represent ordinary arrays, lists, 220 symbol tables, sets, records, graphs, trees, etc. 221 To represent records, Lua uses the field name as an index. 222 The language supports this representation by 223 providing <code>a.name</code> as syntactic sugar for <code>a["name"]</code>. 224 There are several convenient ways to create tables in Lua 225 (see <a href="#3.4.9">§3.4.9</a>). 226 227 228 <p> 229 Like indices, 230 the values of table fields can be of any type. 231 In particular, 232 because functions are first-class values, 233 table fields can contain functions. 234 Thus tables can also carry <em>methods</em> (see <a href="#3.4.11">§3.4.11</a>). 235 236 237 <p> 238 The indexing of tables follows 239 the definition of raw equality in the language. 240 The expressions <code>a[i]</code> and <code>a[j]</code> 241 denote the same table element 242 if and only if <code>i</code> and <code>j</code> are raw equal 243 (that is, equal without metamethods). 244 In particular, floats with integral values 245 are equal to their respective integers 246 (e.g., <code>1.0 == 1</code>). 247 To avoid ambiguities, 248 any float with integral value used as a key 249 is converted to its respective integer. 250 For instance, if you write <code>a[2.0] = true</code>, 251 the actual key inserted into the table will be the 252 integer <code>2</code>. 253 (On the other hand, 254 2 and "<code>2</code>" are different Lua values and therefore 255 denote different table entries.) 256 257 258 <p> 259 Tables, functions, threads, and (full) userdata values are <em>objects</em>: 260 variables do not actually <em>contain</em> these values, 261 only <em>references</em> to them. 262 Assignment, parameter passing, and function returns 263 always manipulate references to such values; 264 these operations do not imply any kind of copy. 265 266 267 <p> 268 The library function <a href="#pdf-type"><code>type</code></a> returns a string describing the type 269 of a given value (see <a href="#6.1">§6.1</a>). 270 271 272 273 274 275 <h2>2.2 – <a name="2.2">Environments and the Global Environment</a></h2> 276 277 <p> 278 As will be discussed in <a href="#3.2">§3.2</a> and <a href="#3.3.3">§3.3.3</a>, 279 any reference to a free name 280 (that is, a name not bound to any declaration) <code>var</code> 281 is syntactically translated to <code>_ENV.var</code>. 282 Moreover, every chunk is compiled in the scope of 283 an external local variable named <code>_ENV</code> (see <a href="#3.3.2">§3.3.2</a>), 284 so <code>_ENV</code> itself is never a free name in a chunk. 285 286 287 <p> 288 Despite the existence of this external <code>_ENV</code> variable and 289 the translation of free names, 290 <code>_ENV</code> is a completely regular name. 291 In particular, 292 you can define new variables and parameters with that name. 293 Each reference to a free name uses the <code>_ENV</code> that is 294 visible at that point in the program, 295 following the usual visibility rules of Lua (see <a href="#3.5">§3.5</a>). 296 297 298 <p> 299 Any table used as the value of <code>_ENV</code> is called an <em>environment</em>. 300 301 302 <p> 303 Lua keeps a distinguished environment called the <em>global environment</em>. 304 This value is kept at a special index in the C registry (see <a href="#4.5">§4.5</a>). 305 In Lua, the global variable <a href="#pdf-_G"><code>_G</code></a> is initialized with this same value. 306 (<a href="#pdf-_G"><code>_G</code></a> is never used internally.) 307 308 309 <p> 310 When Lua loads a chunk, 311 the default value for its <code>_ENV</code> upvalue 312 is the global environment (see <a href="#pdf-load"><code>load</code></a>). 313 Therefore, by default, 314 free names in Lua code refer to entries in the global environment 315 (and, therefore, they are also called <em>global variables</em>). 316 Moreover, all standard libraries are loaded in the global environment 317 and some functions there operate on that environment. 318 You can use <a href="#pdf-load"><code>load</code></a> (or <a href="#pdf-loadfile"><code>loadfile</code></a>) 319 to load a chunk with a different environment. 320 (In C, you have to load the chunk and then change the value 321 of its first upvalue.) 322 323 324 325 326 327 <h2>2.3 – <a name="2.3">Error Handling</a></h2> 328 329 <p> 330 Because Lua is an embedded extension language, 331 all Lua actions start from C code in the host program 332 calling a function from the Lua library. 333 (When you use Lua standalone, 334 the <code>lua</code> application is the host program.) 335 Whenever an error occurs during 336 the compilation or execution of a Lua chunk, 337 control returns to the host, 338 which can take appropriate measures 339 (such as printing an error message). 340 341 342 <p> 343 Lua code can explicitly generate an error by calling the 344 <a href="#pdf-error"><code>error</code></a> function. 345 If you need to catch errors in Lua, 346 you can use <a href="#pdf-pcall"><code>pcall</code></a> or <a href="#pdf-xpcall"><code>xpcall</code></a> 347 to call a given function in <em>protected mode</em>. 348 349 350 <p> 351 Whenever there is an error, 352 an <em>error object</em> (also called an <em>error message</em>) 353 is propagated with information about the error. 354 Lua itself only generates errors whose error object is a string, 355 but programs may generate errors with 356 any value as the error object. 357 It is up to the Lua program or its host to handle such error objects. 358 359 360 <p> 361 When you use <a href="#pdf-xpcall"><code>xpcall</code></a> or <a href="#lua_pcall"><code>lua_pcall</code></a>, 362 you may give a <em>message handler</em> 363 to be called in case of errors. 364 This function is called with the original error object 365 and returns a new error object. 366 It is called before the error unwinds the stack, 367 so that it can gather more information about the error, 368 for instance by inspecting the stack and creating a stack traceback. 369 This message handler is still protected by the protected call; 370 so, an error inside the message handler 371 will call the message handler again. 372 If this loop goes on for too long, 373 Lua breaks it and returns an appropriate message. 374 (The message handler is called only for regular runtime errors. 375 It is not called for memory-allocation errors 376 nor for errors while running finalizers.) 377 378 379 380 381 382 <h2>2.4 – <a name="2.4">Metatables and Metamethods</a></h2> 383 384 <p> 385 Every value in Lua can have a <em>metatable</em>. 386 This <em>metatable</em> is an ordinary Lua table 387 that defines the behavior of the original value 388 under certain special operations. 389 You can change several aspects of the behavior 390 of operations over a value by setting specific fields in its metatable. 391 For instance, when a non-numeric value is the operand of an addition, 392 Lua checks for a function in the field "<code>__add</code>" of the value's metatable. 393 If it finds one, 394 Lua calls this function to perform the addition. 395 396 397 <p> 398 The key for each event in a metatable is a string 399 with the event name prefixed by two underscores; 400 the corresponding values are called <em>metamethods</em>. 401 In the previous example, the key is "<code>__add</code>" 402 and the metamethod is the function that performs the addition. 403 Unless stated otherwise, 404 metamethods should be function values. 405 406 407 <p> 408 You can query the metatable of any value 409 using the <a href="#pdf-getmetatable"><code>getmetatable</code></a> function. 410 Lua queries metamethods in metatables using a raw access (see <a href="#pdf-rawget"><code>rawget</code></a>). 411 So, to retrieve the metamethod for event <code>ev</code> in object <code>o</code>, 412 Lua does the equivalent to the following code: 413 414 <pre> 415 rawget(getmetatable(<em>o</em>) or {}, "__<em>ev</em>") 416 </pre> 417 418 <p> 419 You can replace the metatable of tables 420 using the <a href="#pdf-setmetatable"><code>setmetatable</code></a> function. 421 You cannot change the metatable of other types from Lua code 422 (except by using the debug library (<a href="#6.10">§6.10</a>)); 423 you should use the C API for that. 424 425 426 <p> 427 Tables and full userdata have individual metatables 428 (although multiple tables and userdata can share their metatables). 429 Values of all other types share one single metatable per type; 430 that is, there is one single metatable for all numbers, 431 one for all strings, etc. 432 By default, a value has no metatable, 433 but the string library sets a metatable for the string type (see <a href="#6.4">§6.4</a>). 434 435 436 <p> 437 A metatable controls how an object behaves in 438 arithmetic operations, bitwise operations, 439 order comparisons, concatenation, length operation, calls, and indexing. 440 A metatable also can define a function to be called 441 when a userdata or a table is garbage collected (<a href="#2.5">§2.5</a>). 442 443 444 <p> 445 For the unary operators (negation, length, and bitwise NOT), 446 the metamethod is computed and called with a dummy second operand, 447 equal to the first one. 448 This extra operand is only to simplify Lua's internals 449 (by making these operators behave like a binary operation) 450 and may be removed in future versions. 451 (For most uses this extra operand is irrelevant.) 452 453 454 <p> 455 A detailed list of events controlled by metatables is given next. 456 Each operation is identified by its corresponding key. 457 458 459 460 <ul> 461 462 <li><b><code>__add</code>: </b> 463 the addition (<code>+</code>) operation. 464 If any operand for an addition is not a number 465 (nor a string coercible to a number), 466 Lua will try to call a metamethod. 467 First, Lua will check the first operand (even if it is valid). 468 If that operand does not define a metamethod for <code>__add</code>, 469 then Lua will check the second operand. 470 If Lua can find a metamethod, 471 it calls the metamethod with the two operands as arguments, 472 and the result of the call 473 (adjusted to one value) 474 is the result of the operation. 475 Otherwise, 476 it raises an error. 477 </li> 478 479 <li><b><code>__sub</code>: </b> 480 the subtraction (<code>-</code>) operation. 481 Behavior similar to the addition operation. 482 </li> 483 484 <li><b><code>__mul</code>: </b> 485 the multiplication (<code>*</code>) operation. 486 Behavior similar to the addition operation. 487 </li> 488 489 <li><b><code>__div</code>: </b> 490 the division (<code>/</code>) operation. 491 Behavior similar to the addition operation. 492 </li> 493 494 <li><b><code>__mod</code>: </b> 495 the modulo (<code>%</code>) operation. 496 Behavior similar to the addition operation. 497 </li> 498 499 <li><b><code>__pow</code>: </b> 500 the exponentiation (<code>^</code>) operation. 501 Behavior similar to the addition operation. 502 </li> 503 504 <li><b><code>__unm</code>: </b> 505 the negation (unary <code>-</code>) operation. 506 Behavior similar to the addition operation. 507 </li> 508 509 <li><b><code>__idiv</code>: </b> 510 the floor division (<code>//</code>) operation. 511 Behavior similar to the addition operation. 512 </li> 513 514 <li><b><code>__band</code>: </b> 515 the bitwise AND (<code>&</code>) operation. 516 Behavior similar to the addition operation, 517 except that Lua will try a metamethod 518 if any operand is neither an integer 519 nor a value coercible to an integer (see <a href="#3.4.3">§3.4.3</a>). 520 </li> 521 522 <li><b><code>__bor</code>: </b> 523 the bitwise OR (<code>|</code>) operation. 524 Behavior similar to the bitwise AND operation. 525 </li> 526 527 <li><b><code>__bxor</code>: </b> 528 the bitwise exclusive OR (binary <code>~</code>) operation. 529 Behavior similar to the bitwise AND operation. 530 </li> 531 532 <li><b><code>__bnot</code>: </b> 533 the bitwise NOT (unary <code>~</code>) operation. 534 Behavior similar to the bitwise AND operation. 535 </li> 536 537 <li><b><code>__shl</code>: </b> 538 the bitwise left shift (<code><<</code>) operation. 539 Behavior similar to the bitwise AND operation. 540 </li> 541 542 <li><b><code>__shr</code>: </b> 543 the bitwise right shift (<code>>></code>) operation. 544 Behavior similar to the bitwise AND operation. 545 </li> 546 547 <li><b><code>__concat</code>: </b> 548 the concatenation (<code>..</code>) operation. 549 Behavior similar to the addition operation, 550 except that Lua will try a metamethod 551 if any operand is neither a string nor a number 552 (which is always coercible to a string). 553 </li> 554 555 <li><b><code>__len</code>: </b> 556 the length (<code>#</code>) operation. 557 If the object is not a string, 558 Lua will try its metamethod. 559 If there is a metamethod, 560 Lua calls it with the object as argument, 561 and the result of the call 562 (always adjusted to one value) 563 is the result of the operation. 564 If there is no metamethod but the object is a table, 565 then Lua uses the table length operation (see <a href="#3.4.7">§3.4.7</a>). 566 Otherwise, Lua raises an error. 567 </li> 568 569 <li><b><code>__eq</code>: </b> 570 the equal (<code>==</code>) operation. 571 Behavior similar to the addition operation, 572 except that Lua will try a metamethod only when the values 573 being compared are either both tables or both full userdata 574 and they are not primitively equal. 575 The result of the call is always converted to a boolean. 576 </li> 577 578 <li><b><code>__lt</code>: </b> 579 the less than (<code><</code>) operation. 580 Behavior similar to the addition operation, 581 except that Lua will try a metamethod only when the values 582 being compared are neither both numbers nor both strings. 583 The result of the call is always converted to a boolean. 584 </li> 585 586 <li><b><code>__le</code>: </b> 587 the less equal (<code><=</code>) operation. 588 Unlike other operations, 589 the less-equal operation can use two different events. 590 First, Lua looks for the <code>__le</code> metamethod in both operands, 591 like in the less than operation. 592 If it cannot find such a metamethod, 593 then it will try the <code>__lt</code> metamethod, 594 assuming that <code>a <= b</code> is equivalent to <code>not (b < a)</code>. 595 As with the other comparison operators, 596 the result is always a boolean. 597 (This use of the <code>__lt</code> event can be removed in future versions; 598 it is also slower than a real <code>__le</code> metamethod.) 599 </li> 600 601 <li><b><code>__index</code>: </b> 602 The indexing access operation <code>table[key]</code>. 603 This event happens when <code>table</code> is not a table or 604 when <code>key</code> is not present in <code>table</code>. 605 The metamethod is looked up in <code>table</code>. 606 607 608 <p> 609 Despite the name, 610 the metamethod for this event can be either a function or a table. 611 If it is a function, 612 it is called with <code>table</code> and <code>key</code> as arguments, 613 and the result of the call 614 (adjusted to one value) 615 is the result of the operation. 616 If it is a table, 617 the final result is the result of indexing this table with <code>key</code>. 618 (This indexing is regular, not raw, 619 and therefore can trigger another metamethod.) 620 </li> 621 622 <li><b><code>__newindex</code>: </b> 623 The indexing assignment <code>table[key] = value</code>. 624 Like the index event, 625 this event happens when <code>table</code> is not a table or 626 when <code>key</code> is not present in <code>table</code>. 627 The metamethod is looked up in <code>table</code>. 628 629 630 <p> 631 Like with indexing, 632 the metamethod for this event can be either a function or a table. 633 If it is a function, 634 it is called with <code>table</code>, <code>key</code>, and <code>value</code> as arguments. 635 If it is a table, 636 Lua does an indexing assignment to this table with the same key and value. 637 (This assignment is regular, not raw, 638 and therefore can trigger another metamethod.) 639 640 641 <p> 642 Whenever there is a <code>__newindex</code> metamethod, 643 Lua does not perform the primitive assignment. 644 (If necessary, 645 the metamethod itself can call <a href="#pdf-rawset"><code>rawset</code></a> 646 to do the assignment.) 647 </li> 648 649 <li><b><code>__call</code>: </b> 650 The call operation <code>func(args)</code>. 651 This event happens when Lua tries to call a non-function value 652 (that is, <code>func</code> is not a function). 653 The metamethod is looked up in <code>func</code>. 654 If present, 655 the metamethod is called with <code>func</code> as its first argument, 656 followed by the arguments of the original call (<code>args</code>). 657 All results of the call 658 are the result of the operation. 659 (This is the only metamethod that allows multiple results.) 660 </li> 661 662 </ul> 663 664 <p> 665 It is a good practice to add all needed metamethods to a table 666 before setting it as a metatable of some object. 667 In particular, the <code>__gc</code> metamethod works only when this order 668 is followed (see <a href="#2.5.1">§2.5.1</a>). 669 670 671 <p> 672 Because metatables are regular tables, 673 they can contain arbitrary fields, 674 not only the event names defined above. 675 Some functions in the standard library 676 (e.g., <a href="#pdf-tostring"><code>tostring</code></a>) 677 use other fields in metatables for their own purposes. 678 679 680 681 682 683 <h2>2.5 – <a name="2.5">Garbage Collection</a></h2> 684 685 <p> 686 Lua performs automatic memory management. 687 This means that 688 you do not have to worry about allocating memory for new objects 689 or freeing it when the objects are no longer needed. 690 Lua manages memory automatically by running 691 a <em>garbage collector</em> to collect all <em>dead objects</em> 692 (that is, objects that are no longer accessible from Lua). 693 All memory used by Lua is subject to automatic management: 694 strings, tables, userdata, functions, threads, internal structures, etc. 695 696 697 <p> 698 Lua implements an incremental mark-and-sweep collector. 699 It uses two numbers to control its garbage-collection cycles: 700 the <em>garbage-collector pause</em> and 701 the <em>garbage-collector step multiplier</em>. 702 Both use percentage points as units 703 (e.g., a value of 100 means an internal value of 1). 704 705 706 <p> 707 The garbage-collector pause 708 controls how long the collector waits before starting a new cycle. 709 Larger values make the collector less aggressive. 710 Values smaller than 100 mean the collector will not wait to 711 start a new cycle. 712 A value of 200 means that the collector waits for the total memory in use 713 to double before starting a new cycle. 714 715 716 <p> 717 The garbage-collector step multiplier 718 controls the relative speed of the collector relative to 719 memory allocation. 720 Larger values make the collector more aggressive but also increase 721 the size of each incremental step. 722 You should not use values smaller than 100, 723 because they make the collector too slow and 724 can result in the collector never finishing a cycle. 725 The default is 200, 726 which means that the collector runs at "twice" 727 the speed of memory allocation. 728 729 730 <p> 731 If you set the step multiplier to a very large number 732 (larger than 10% of the maximum number of 733 bytes that the program may use), 734 the collector behaves like a stop-the-world collector. 735 If you then set the pause to 200, 736 the collector behaves as in old Lua versions, 737 doing a complete collection every time Lua doubles its 738 memory usage. 739 740 741 <p> 742 You can change these numbers by calling <a href="#lua_gc"><code>lua_gc</code></a> in C 743 or <a href="#pdf-collectgarbage"><code>collectgarbage</code></a> in Lua. 744 You can also use these functions to control 745 the collector directly (e.g., stop and restart it). 746 747 748 749 <h3>2.5.1 – <a name="2.5.1">Garbage-Collection Metamethods</a></h3> 750 751 <p> 752 You can set garbage-collector metamethods for tables 753 and, using the C API, 754 for full userdata (see <a href="#2.4">§2.4</a>). 755 These metamethods are also called <em>finalizers</em>. 756 Finalizers allow you to coordinate Lua's garbage collection 757 with external resource management 758 (such as closing files, network or database connections, 759 or freeing your own memory). 760 761 762 <p> 763 For an object (table or userdata) to be finalized when collected, 764 you must <em>mark</em> it for finalization. 765 766 You mark an object for finalization when you set its metatable 767 and the metatable has a field indexed by the string "<code>__gc</code>". 768 Note that if you set a metatable without a <code>__gc</code> field 769 and later create that field in the metatable, 770 the object will not be marked for finalization. 771 772 773 <p> 774 When a marked object becomes garbage, 775 it is not collected immediately by the garbage collector. 776 Instead, Lua puts it in a list. 777 After the collection, 778 Lua goes through that list. 779 For each object in the list, 780 it checks the object's <code>__gc</code> metamethod: 781 If it is a function, 782 Lua calls it with the object as its single argument; 783 if the metamethod is not a function, 784 Lua simply ignores it. 785 786 787 <p> 788 At the end of each garbage-collection cycle, 789 the finalizers for objects are called in 790 the reverse order that the objects were marked for finalization, 791 among those collected in that cycle; 792 that is, the first finalizer to be called is the one associated 793 with the object marked last in the program. 794 The execution of each finalizer may occur at any point during 795 the execution of the regular code. 796 797 798 <p> 799 Because the object being collected must still be used by the finalizer, 800 that object (and other objects accessible only through it) 801 must be <em>resurrected</em> by Lua. 802 Usually, this resurrection is transient, 803 and the object memory is freed in the next garbage-collection cycle. 804 However, if the finalizer stores the object in some global place 805 (e.g., a global variable), 806 then the resurrection is permanent. 807 Moreover, if the finalizer marks a finalizing object for finalization again, 808 its finalizer will be called again in the next cycle where the 809 object is unreachable. 810 In any case, 811 the object memory is freed only in a GC cycle where 812 the object is unreachable and not marked for finalization. 813 814 815 <p> 816 When you close a state (see <a href="#lua_close"><code>lua_close</code></a>), 817 Lua calls the finalizers of all objects marked for finalization, 818 following the reverse order that they were marked. 819 If any finalizer marks objects for collection during that phase, 820 these marks have no effect. 821 822 823 824 825 826 <h3>2.5.2 – <a name="2.5.2">Weak Tables</a></h3> 827 828 <p> 829 A <em>weak table</em> is a table whose elements are 830 <em>weak references</em>. 831 A weak reference is ignored by the garbage collector. 832 In other words, 833 if the only references to an object are weak references, 834 then the garbage collector will collect that object. 835 836 837 <p> 838 A weak table can have weak keys, weak values, or both. 839 A table with weak values allows the collection of its values, 840 but prevents the collection of its keys. 841 A table with both weak keys and weak values allows the collection of 842 both keys and values. 843 In any case, if either the key or the value is collected, 844 the whole pair is removed from the table. 845 The weakness of a table is controlled by the 846 <code>__mode</code> field of its metatable. 847 If the <code>__mode</code> field is a string containing the character '<code>k</code>', 848 the keys in the table are weak. 849 If <code>__mode</code> contains '<code>v</code>', 850 the values in the table are weak. 851 852 853 <p> 854 A table with weak keys and strong values 855 is also called an <em>ephemeron table</em>. 856 In an ephemeron table, 857 a value is considered reachable only if its key is reachable. 858 In particular, 859 if the only reference to a key comes through its value, 860 the pair is removed. 861 862 863 <p> 864 Any change in the weakness of a table may take effect only 865 at the next collect cycle. 866 In particular, if you change the weakness to a stronger mode, 867 Lua may still collect some items from that table 868 before the change takes effect. 869 870 871 <p> 872 Only objects that have an explicit construction 873 are removed from weak tables. 874 Values, such as numbers and light C functions, 875 are not subject to garbage collection, 876 and therefore are not removed from weak tables 877 (unless their associated values are collected). 878 Although strings are subject to garbage collection, 879 they do not have an explicit construction, 880 and therefore are not removed from weak tables. 881 882 883 <p> 884 Resurrected objects 885 (that is, objects being finalized 886 and objects accessible only through objects being finalized) 887 have a special behavior in weak tables. 888 They are removed from weak values before running their finalizers, 889 but are removed from weak keys only in the next collection 890 after running their finalizers, when such objects are actually freed. 891 This behavior allows the finalizer to access properties 892 associated with the object through weak tables. 893 894 895 <p> 896 If a weak table is among the resurrected objects in a collection cycle, 897 it may not be properly cleared until the next cycle. 898 899 900 901 902 903 904 905 <h2>2.6 – <a name="2.6">Coroutines</a></h2> 906 907 <p> 908 Lua supports coroutines, 909 also called <em>collaborative multithreading</em>. 910 A coroutine in Lua represents an independent thread of execution. 911 Unlike threads in multithread systems, however, 912 a coroutine only suspends its execution by explicitly calling 913 a yield function. 914 915 916 <p> 917 You create a coroutine by calling <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>. 918 Its sole argument is a function 919 that is the main function of the coroutine. 920 The <code>create</code> function only creates a new coroutine and 921 returns a handle to it (an object of type <em>thread</em>); 922 it does not start the coroutine. 923 924 925 <p> 926 You execute a coroutine by calling <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. 927 When you first call <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, 928 passing as its first argument 929 a thread returned by <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, 930 the coroutine starts its execution by 931 calling its main function. 932 Extra arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> are passed 933 as arguments to that function. 934 After the coroutine starts running, 935 it runs until it terminates or <em>yields</em>. 936 937 938 <p> 939 A coroutine can terminate its execution in two ways: 940 normally, when its main function returns 941 (explicitly or implicitly, after the last instruction); 942 and abnormally, if there is an unprotected error. 943 In case of normal termination, 944 <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>true</b>, 945 plus any values returned by the coroutine main function. 946 In case of errors, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns <b>false</b> 947 plus an error object. 948 949 950 <p> 951 A coroutine yields by calling <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. 952 When a coroutine yields, 953 the corresponding <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> returns immediately, 954 even if the yield happens inside nested function calls 955 (that is, not in the main function, 956 but in a function directly or indirectly called by the main function). 957 In the case of a yield, <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a> also returns <b>true</b>, 958 plus any values passed to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a>. 959 The next time you resume the same coroutine, 960 it continues its execution from the point where it yielded, 961 with the call to <a href="#pdf-coroutine.yield"><code>coroutine.yield</code></a> returning any extra 962 arguments passed to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. 963 964 965 <p> 966 Like <a href="#pdf-coroutine.create"><code>coroutine.create</code></a>, 967 the <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> function also creates a coroutine, 968 but instead of returning the coroutine itself, 969 it returns a function that, when called, resumes the coroutine. 970 Any arguments passed to this function 971 go as extra arguments to <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>. 972 <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> returns all the values returned by <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, 973 except the first one (the boolean error code). 974 Unlike <a href="#pdf-coroutine.resume"><code>coroutine.resume</code></a>, 975 <a href="#pdf-coroutine.wrap"><code>coroutine.wrap</code></a> does not catch errors; 976 any error is propagated to the caller. 977 978 979 <p> 980 As an example of how coroutines work, 981 consider the following code: 982 983 <pre> 984 function foo (a) 985 print("foo", a) 986 return coroutine.yield(2*a) 987 end 988 989 co = coroutine.create(function (a,b) 990 print("co-body", a, b) 991 local r = foo(a+1) 992 print("co-body", r) 993 local r, s = coroutine.yield(a+b, a-b) 994 print("co-body", r, s) 995 return b, "end" 996 end) 997 998 print("main", coroutine.resume(co, 1, 10)) 999 print("main", coroutine.resume(co, "r")) 1000 print("main", coroutine.resume(co, "x", "y")) 1001 print("main", coroutine.resume(co, "x", "y")) 1002 </pre><p> 1003 When you run it, it produces the following output: 1004 1005 <pre> 1006 co-body 1 10 1007 foo 2 1008 main true 4 1009 co-body r 1010 main true 11 -9 1011 co-body x y 1012 main true 10 end 1013 main false cannot resume dead coroutine 1014 </pre> 1015 1016 <p> 1017 You can also create and manipulate coroutines through the C API: 1018 see functions <a href="#lua_newthread"><code>lua_newthread</code></a>, <a href="#lua_resume"><code>lua_resume</code></a>, 1019 and <a href="#lua_yield"><code>lua_yield</code></a>. 1020 1021 1022 1023 1024 1025 <h1>3 – <a name="3">The Language</a></h1> 1026 1027 <p> 1028 This section describes the lexis, the syntax, and the semantics of Lua. 1029 In other words, 1030 this section describes 1031 which tokens are valid, 1032 how they can be combined, 1033 and what their combinations mean. 1034 1035 1036 <p> 1037 Language constructs will be explained using the usual extended BNF notation, 1038 in which 1039 {<em>a</em>} means 0 or more <em>a</em>'s, and 1040 [<em>a</em>] means an optional <em>a</em>. 1041 Non-terminals are shown like non-terminal, 1042 keywords are shown like <b>kword</b>, 1043 and other terminal symbols are shown like ‘<b>=</b>’. 1044 The complete syntax of Lua can be found in <a href="#9">§9</a> 1045 at the end of this manual. 1046 1047 1048 1049 <h2>3.1 – <a name="3.1">Lexical Conventions</a></h2> 1050 1051 <p> 1052 Lua is a free-form language. 1053 It ignores spaces (including new lines) and comments 1054 between lexical elements (tokens), 1055 except as delimiters between names and keywords. 1056 1057 1058 <p> 1059 <em>Names</em> 1060 (also called <em>identifiers</em>) 1061 in Lua can be any string of letters, 1062 digits, and underscores, 1063 not beginning with a digit and 1064 not being a reserved word. 1065 Identifiers are used to name variables, table fields, and labels. 1066 1067 1068 <p> 1069 The following <em>keywords</em> are reserved 1070 and cannot be used as names: 1071 1072 1073 <pre> 1074 and break do else elseif end 1075 false for function goto if in 1076 local nil not or repeat return 1077 then true until while 1078 </pre> 1079 1080 <p> 1081 Lua is a case-sensitive language: 1082 <code>and</code> is a reserved word, but <code>And</code> and <code>AND</code> 1083 are two different, valid names. 1084 As a convention, 1085 programs should avoid creating 1086 names that start with an underscore followed by 1087 one or more uppercase letters (such as <a href="#pdf-_VERSION"><code>_VERSION</code></a>). 1088 1089 1090 <p> 1091 The following strings denote other tokens: 1092 1093 <pre> 1094 + - * / % ^ # 1095 & ~ | << >> // 1096 == ~= <= >= < > = 1097 ( ) { } [ ] :: 1098 ; : , . .. ... 1099 </pre> 1100 1101 <p> 1102 A <em>short literal string</em> 1103 can be delimited by matching single or double quotes, 1104 and can contain the following C-like escape sequences: 1105 '<code>\a</code>' (bell), 1106 '<code>\b</code>' (backspace), 1107 '<code>\f</code>' (form feed), 1108 '<code>\n</code>' (newline), 1109 '<code>\r</code>' (carriage return), 1110 '<code>\t</code>' (horizontal tab), 1111 '<code>\v</code>' (vertical tab), 1112 '<code>\\</code>' (backslash), 1113 '<code>\"</code>' (quotation mark [double quote]), 1114 and '<code>\'</code>' (apostrophe [single quote]). 1115 A backslash followed by a line break 1116 results in a newline in the string. 1117 The escape sequence '<code>\z</code>' skips the following span 1118 of white-space characters, 1119 including line breaks; 1120 it is particularly useful to break and indent a long literal string 1121 into multiple lines without adding the newlines and spaces 1122 into the string contents. 1123 A short literal string cannot contain unescaped line breaks 1124 nor escapes not forming a valid escape sequence. 1125 1126 1127 <p> 1128 We can specify any byte in a short literal string by its numeric value 1129 (including embedded zeros). 1130 This can be done 1131 with the escape sequence <code>\x<em>XX</em></code>, 1132 where <em>XX</em> is a sequence of exactly two hexadecimal digits, 1133 or with the escape sequence <code>\<em>ddd</em></code>, 1134 where <em>ddd</em> is a sequence of up to three decimal digits. 1135 (Note that if a decimal escape sequence is to be followed by a digit, 1136 it must be expressed using exactly three digits.) 1137 1138 1139 <p> 1140 The UTF-8 encoding of a Unicode character 1141 can be inserted in a literal string with 1142 the escape sequence <code>\u{<em>XXX</em>}</code> 1143 (note the mandatory enclosing brackets), 1144 where <em>XXX</em> is a sequence of one or more hexadecimal digits 1145 representing the character code point. 1146 1147 1148 <p> 1149 Literal strings can also be defined using a long format 1150 enclosed by <em>long brackets</em>. 1151 We define an <em>opening long bracket of level <em>n</em></em> as an opening 1152 square bracket followed by <em>n</em> equal signs followed by another 1153 opening square bracket. 1154 So, an opening long bracket of level 0 is written as <code>[[</code>, 1155 an opening long bracket of level 1 is written as <code>[=[</code>, 1156 and so on. 1157 A <em>closing long bracket</em> is defined similarly; 1158 for instance, 1159 a closing long bracket of level 4 is written as <code>]====]</code>. 1160 A <em>long literal</em> starts with an opening long bracket of any level and 1161 ends at the first closing long bracket of the same level. 1162 It can contain any text except a closing bracket of the same level. 1163 Literals in this bracketed form can run for several lines, 1164 do not interpret any escape sequences, 1165 and ignore long brackets of any other level. 1166 Any kind of end-of-line sequence 1167 (carriage return, newline, carriage return followed by newline, 1168 or newline followed by carriage return) 1169 is converted to a simple newline. 1170 1171 1172 <p> 1173 For convenience, 1174 when the opening long bracket is immediately followed by a newline, 1175 the newline is not included in the string. 1176 As an example, in a system using ASCII 1177 (in which '<code>a</code>' is coded as 97, 1178 newline is coded as 10, and '<code>1</code>' is coded as 49), 1179 the five literal strings below denote the same string: 1180 1181 <pre> 1182 a = 'alo\n123"' 1183 a = "alo\n123\"" 1184 a = '\97lo\10\04923"' 1185 a = [[alo 1186 123"]] 1187 a = [==[ 1188 alo 1189 123"]==] 1190 </pre> 1191 1192 <p> 1193 Any byte in a literal string not 1194 explicitly affected by the previous rules represents itself. 1195 However, Lua opens files for parsing in text mode, 1196 and the system file functions may have problems with 1197 some control characters. 1198 So, it is safer to represent 1199 non-text data as a quoted literal with 1200 explicit escape sequences for the non-text characters. 1201 1202 1203 <p> 1204 A <em>numeric constant</em> (or <em>numeral</em>) 1205 can be written with an optional fractional part 1206 and an optional decimal exponent, 1207 marked by a letter '<code>e</code>' or '<code>E</code>'. 1208 Lua also accepts hexadecimal constants, 1209 which start with <code>0x</code> or <code>0X</code>. 1210 Hexadecimal constants also accept an optional fractional part 1211 plus an optional binary exponent, 1212 marked by a letter '<code>p</code>' or '<code>P</code>'. 1213 A numeric constant with a radix point or an exponent 1214 denotes a float; 1215 otherwise, 1216 if its value fits in an integer, 1217 it denotes an integer. 1218 Examples of valid integer constants are 1219 1220 <pre> 1221 3 345 0xff 0xBEBADA 1222 </pre><p> 1223 Examples of valid float constants are 1224 1225 <pre> 1226 3.0 3.1416 314.16e-2 0.31416E1 34e1 1227 0x0.1E 0xA23p-4 0X1.921FB54442D18P+1 1228 </pre> 1229 1230 <p> 1231 A <em>comment</em> starts with a double hyphen (<code>--</code>) 1232 anywhere outside a string. 1233 If the text immediately after <code>--</code> is not an opening long bracket, 1234 the comment is a <em>short comment</em>, 1235 which runs until the end of the line. 1236 Otherwise, it is a <em>long comment</em>, 1237 which runs until the corresponding closing long bracket. 1238 Long comments are frequently used to disable code temporarily. 1239 1240 1241 1242 1243 1244 <h2>3.2 – <a name="3.2">Variables</a></h2> 1245 1246 <p> 1247 Variables are places that store values. 1248 There are three kinds of variables in Lua: 1249 global variables, local variables, and table fields. 1250 1251 1252 <p> 1253 A single name can denote a global variable or a local variable 1254 (or a function's formal parameter, 1255 which is a particular kind of local variable): 1256 1257 <pre> 1258 var ::= Name 1259 </pre><p> 1260 Name denotes identifiers, as defined in <a href="#3.1">§3.1</a>. 1261 1262 1263 <p> 1264 Any variable name is assumed to be global unless explicitly declared 1265 as a local (see <a href="#3.3.7">§3.3.7</a>). 1266 Local variables are <em>lexically scoped</em>: 1267 local variables can be freely accessed by functions 1268 defined inside their scope (see <a href="#3.5">§3.5</a>). 1269 1270 1271 <p> 1272 Before the first assignment to a variable, its value is <b>nil</b>. 1273 1274 1275 <p> 1276 Square brackets are used to index a table: 1277 1278 <pre> 1279 var ::= prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ 1280 </pre><p> 1281 The meaning of accesses to table fields can be changed via metatables 1282 (see <a href="#2.4">§2.4</a>). 1283 1284 1285 <p> 1286 The syntax <code>var.Name</code> is just syntactic sugar for 1287 <code>var["Name"]</code>: 1288 1289 <pre> 1290 var ::= prefixexp ‘<b>.</b>’ Name 1291 </pre> 1292 1293 <p> 1294 An access to a global variable <code>x</code> 1295 is equivalent to <code>_ENV.x</code>. 1296 Due to the way that chunks are compiled, 1297 <code>_ENV</code> is never a global name (see <a href="#2.2">§2.2</a>). 1298 1299 1300 1301 1302 1303 <h2>3.3 – <a name="3.3">Statements</a></h2> 1304 1305 <p> 1306 Lua supports an almost conventional set of statements, 1307 similar to those in Pascal or C. 1308 This set includes 1309 assignments, control structures, function calls, 1310 and variable declarations. 1311 1312 1313 1314 <h3>3.3.1 – <a name="3.3.1">Blocks</a></h3> 1315 1316 <p> 1317 A block is a list of statements, 1318 which are executed sequentially: 1319 1320 <pre> 1321 block ::= {stat} 1322 </pre><p> 1323 Lua has <em>empty statements</em> 1324 that allow you to separate statements with semicolons, 1325 start a block with a semicolon 1326 or write two semicolons in sequence: 1327 1328 <pre> 1329 stat ::= ‘<b>;</b>’ 1330 </pre> 1331 1332 <p> 1333 Function calls and assignments 1334 can start with an open parenthesis. 1335 This possibility leads to an ambiguity in Lua's grammar. 1336 Consider the following fragment: 1337 1338 <pre> 1339 a = b + c 1340 (print or io.write)('done') 1341 </pre><p> 1342 The grammar could see it in two ways: 1343 1344 <pre> 1345 a = b + c(print or io.write)('done') 1346 1347 a = b + c; (print or io.write)('done') 1348 </pre><p> 1349 The current parser always sees such constructions 1350 in the first way, 1351 interpreting the open parenthesis 1352 as the start of the arguments to a call. 1353 To avoid this ambiguity, 1354 it is a good practice to always precede with a semicolon 1355 statements that start with a parenthesis: 1356 1357 <pre> 1358 ;(print or io.write)('done') 1359 </pre> 1360 1361 <p> 1362 A block can be explicitly delimited to produce a single statement: 1363 1364 <pre> 1365 stat ::= <b>do</b> block <b>end</b> 1366 </pre><p> 1367 Explicit blocks are useful 1368 to control the scope of variable declarations. 1369 Explicit blocks are also sometimes used to 1370 add a <b>return</b> statement in the middle 1371 of another block (see <a href="#3.3.4">§3.3.4</a>). 1372 1373 1374 1375 1376 1377 <h3>3.3.2 – <a name="3.3.2">Chunks</a></h3> 1378 1379 <p> 1380 The unit of compilation of Lua is called a <em>chunk</em>. 1381 Syntactically, 1382 a chunk is simply a block: 1383 1384 <pre> 1385 chunk ::= block 1386 </pre> 1387 1388 <p> 1389 Lua handles a chunk as the body of an anonymous function 1390 with a variable number of arguments 1391 (see <a href="#3.4.11">§3.4.11</a>). 1392 As such, chunks can define local variables, 1393 receive arguments, and return values. 1394 Moreover, such anonymous function is compiled as in the 1395 scope of an external local variable called <code>_ENV</code> (see <a href="#2.2">§2.2</a>). 1396 The resulting function always has <code>_ENV</code> as its only upvalue, 1397 even if it does not use that variable. 1398 1399 1400 <p> 1401 A chunk can be stored in a file or in a string inside the host program. 1402 To execute a chunk, 1403 Lua first <em>loads</em> it, 1404 precompiling the chunk's code into instructions for a virtual machine, 1405 and then Lua executes the compiled code 1406 with an interpreter for the virtual machine. 1407 1408 1409 <p> 1410 Chunks can also be precompiled into binary form; 1411 see program <code>luac</code> and function <a href="#pdf-string.dump"><code>string.dump</code></a> for details. 1412 Programs in source and compiled forms are interchangeable; 1413 Lua automatically detects the file type and acts accordingly (see <a href="#pdf-load"><code>load</code></a>). 1414 1415 1416 1417 1418 1419 <h3>3.3.3 – <a name="3.3.3">Assignment</a></h3> 1420 1421 <p> 1422 Lua allows multiple assignments. 1423 Therefore, the syntax for assignment 1424 defines a list of variables on the left side 1425 and a list of expressions on the right side. 1426 The elements in both lists are separated by commas: 1427 1428 <pre> 1429 stat ::= varlist ‘<b>=</b>’ explist 1430 varlist ::= var {‘<b>,</b>’ var} 1431 explist ::= exp {‘<b>,</b>’ exp} 1432 </pre><p> 1433 Expressions are discussed in <a href="#3.4">§3.4</a>. 1434 1435 1436 <p> 1437 Before the assignment, 1438 the list of values is <em>adjusted</em> to the length of 1439 the list of variables. 1440 If there are more values than needed, 1441 the excess values are thrown away. 1442 If there are fewer values than needed, 1443 the list is extended with as many <b>nil</b>'s as needed. 1444 If the list of expressions ends with a function call, 1445 then all values returned by that call enter the list of values, 1446 before the adjustment 1447 (except when the call is enclosed in parentheses; see <a href="#3.4">§3.4</a>). 1448 1449 1450 <p> 1451 The assignment statement first evaluates all its expressions 1452 and only then the assignments are performed. 1453 Thus the code 1454 1455 <pre> 1456 i = 3 1457 i, a[i] = i+1, 20 1458 </pre><p> 1459 sets <code>a[3]</code> to 20, without affecting <code>a[4]</code> 1460 because the <code>i</code> in <code>a[i]</code> is evaluated (to 3) 1461 before it is assigned 4. 1462 Similarly, the line 1463 1464 <pre> 1465 x, y = y, x 1466 </pre><p> 1467 exchanges the values of <code>x</code> and <code>y</code>, 1468 and 1469 1470 <pre> 1471 x, y, z = y, z, x 1472 </pre><p> 1473 cyclically permutes the values of <code>x</code>, <code>y</code>, and <code>z</code>. 1474 1475 1476 <p> 1477 An assignment to a global name <code>x = val</code> 1478 is equivalent to the assignment 1479 <code>_ENV.x = val</code> (see <a href="#2.2">§2.2</a>). 1480 1481 1482 <p> 1483 The meaning of assignments to table fields and 1484 global variables (which are actually table fields, too) 1485 can be changed via metatables (see <a href="#2.4">§2.4</a>). 1486 1487 1488 1489 1490 1491 <h3>3.3.4 – <a name="3.3.4">Control Structures</a></h3><p> 1492 The control structures 1493 <b>if</b>, <b>while</b>, and <b>repeat</b> have the usual meaning and 1494 familiar syntax: 1495 1496 1497 1498 1499 <pre> 1500 stat ::= <b>while</b> exp <b>do</b> block <b>end</b> 1501 stat ::= <b>repeat</b> block <b>until</b> exp 1502 stat ::= <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> 1503 </pre><p> 1504 Lua also has a <b>for</b> statement, in two flavors (see <a href="#3.3.5">§3.3.5</a>). 1505 1506 1507 <p> 1508 The condition expression of a 1509 control structure can return any value. 1510 Both <b>false</b> and <b>nil</b> are considered false. 1511 All values different from <b>nil</b> and <b>false</b> are considered true 1512 (in particular, the number 0 and the empty string are also true). 1513 1514 1515 <p> 1516 In the <b>repeat</b>–<b>until</b> loop, 1517 the inner block does not end at the <b>until</b> keyword, 1518 but only after the condition. 1519 So, the condition can refer to local variables 1520 declared inside the loop block. 1521 1522 1523 <p> 1524 The <b>goto</b> statement transfers the program control to a label. 1525 For syntactical reasons, 1526 labels in Lua are considered statements too: 1527 1528 1529 1530 <pre> 1531 stat ::= <b>goto</b> Name 1532 stat ::= label 1533 label ::= ‘<b>::</b>’ Name ‘<b>::</b>’ 1534 </pre> 1535 1536 <p> 1537 A label is visible in the entire block where it is defined, 1538 except 1539 inside nested blocks where a label with the same name is defined and 1540 inside nested functions. 1541 A goto may jump to any visible label as long as it does not 1542 enter into the scope of a local variable. 1543 1544 1545 <p> 1546 Labels and empty statements are called <em>void statements</em>, 1547 as they perform no actions. 1548 1549 1550 <p> 1551 The <b>break</b> statement terminates the execution of a 1552 <b>while</b>, <b>repeat</b>, or <b>for</b> loop, 1553 skipping to the next statement after the loop: 1554 1555 1556 <pre> 1557 stat ::= <b>break</b> 1558 </pre><p> 1559 A <b>break</b> ends the innermost enclosing loop. 1560 1561 1562 <p> 1563 The <b>return</b> statement is used to return values 1564 from a function or a chunk 1565 (which is an anonymous function). 1566 1567 Functions can return more than one value, 1568 so the syntax for the <b>return</b> statement is 1569 1570 <pre> 1571 stat ::= <b>return</b> [explist] [‘<b>;</b>’] 1572 </pre> 1573 1574 <p> 1575 The <b>return</b> statement can only be written 1576 as the last statement of a block. 1577 If it is really necessary to <b>return</b> in the middle of a block, 1578 then an explicit inner block can be used, 1579 as in the idiom <code>do return end</code>, 1580 because now <b>return</b> is the last statement in its (inner) block. 1581 1582 1583 1584 1585 1586 <h3>3.3.5 – <a name="3.3.5">For Statement</a></h3> 1587 1588 <p> 1589 1590 The <b>for</b> statement has two forms: 1591 one numerical and one generic. 1592 1593 1594 <p> 1595 The numerical <b>for</b> loop repeats a block of code while a 1596 control variable runs through an arithmetic progression. 1597 It has the following syntax: 1598 1599 <pre> 1600 stat ::= <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> 1601 </pre><p> 1602 The <em>block</em> is repeated for <em>name</em> starting at the value of 1603 the first <em>exp</em>, until it passes the second <em>exp</em> by steps of the 1604 third <em>exp</em>. 1605 More precisely, a <b>for</b> statement like 1606 1607 <pre> 1608 for v = <em>e1</em>, <em>e2</em>, <em>e3</em> do <em>block</em> end 1609 </pre><p> 1610 is equivalent to the code: 1611 1612 <pre> 1613 do 1614 local <em>var</em>, <em>limit</em>, <em>step</em> = tonumber(<em>e1</em>), tonumber(<em>e2</em>), tonumber(<em>e3</em>) 1615 if not (<em>var</em> and <em>limit</em> and <em>step</em>) then error() end 1616 <em>var</em> = <em>var</em> - <em>step</em> 1617 while true do 1618 <em>var</em> = <em>var</em> + <em>step</em> 1619 if (<em>step</em> >= 0 and <em>var</em> > <em>limit</em>) or (<em>step</em> < 0 and <em>var</em> < <em>limit</em>) then 1620 break 1621 end 1622 local v = <em>var</em> 1623 <em>block</em> 1624 end 1625 end 1626 </pre> 1627 1628 <p> 1629 Note the following: 1630 1631 <ul> 1632 1633 <li> 1634 All three control expressions are evaluated only once, 1635 before the loop starts. 1636 They must all result in numbers. 1637 </li> 1638 1639 <li> 1640 <code><em>var</em></code>, <code><em>limit</em></code>, and <code><em>step</em></code> are invisible variables. 1641 The names shown here are for explanatory purposes only. 1642 </li> 1643 1644 <li> 1645 If the third expression (the step) is absent, 1646 then a step of 1 is used. 1647 </li> 1648 1649 <li> 1650 You can use <b>break</b> and <b>goto</b> to exit a <b>for</b> loop. 1651 </li> 1652 1653 <li> 1654 The loop variable <code>v</code> is local to the loop body. 1655 If you need its value after the loop, 1656 assign it to another variable before exiting the loop. 1657 </li> 1658 1659 </ul> 1660 1661 <p> 1662 The generic <b>for</b> statement works over functions, 1663 called <em>iterators</em>. 1664 On each iteration, the iterator function is called to produce a new value, 1665 stopping when this new value is <b>nil</b>. 1666 The generic <b>for</b> loop has the following syntax: 1667 1668 <pre> 1669 stat ::= <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> 1670 namelist ::= Name {‘<b>,</b>’ Name} 1671 </pre><p> 1672 A <b>for</b> statement like 1673 1674 <pre> 1675 for <em>var_1</em>, ···, <em>var_n</em> in <em>explist</em> do <em>block</em> end 1676 </pre><p> 1677 is equivalent to the code: 1678 1679 <pre> 1680 do 1681 local <em>f</em>, <em>s</em>, <em>var</em> = <em>explist</em> 1682 while true do 1683 local <em>var_1</em>, ···, <em>var_n</em> = <em>f</em>(<em>s</em>, <em>var</em>) 1684 if <em>var_1</em> == nil then break end 1685 <em>var</em> = <em>var_1</em> 1686 <em>block</em> 1687 end 1688 end 1689 </pre><p> 1690 Note the following: 1691 1692 <ul> 1693 1694 <li> 1695 <code><em>explist</em></code> is evaluated only once. 1696 Its results are an <em>iterator</em> function, 1697 a <em>state</em>, 1698 and an initial value for the first <em>iterator variable</em>. 1699 </li> 1700 1701 <li> 1702 <code><em>f</em></code>, <code><em>s</em></code>, and <code><em>var</em></code> are invisible variables. 1703 The names are here for explanatory purposes only. 1704 </li> 1705 1706 <li> 1707 You can use <b>break</b> to exit a <b>for</b> loop. 1708 </li> 1709 1710 <li> 1711 The loop variables <code><em>var_i</em></code> are local to the loop; 1712 you cannot use their values after the <b>for</b> ends. 1713 If you need these values, 1714 then assign them to other variables before breaking or exiting the loop. 1715 </li> 1716 1717 </ul> 1718 1719 1720 1721 1722 <h3>3.3.6 – <a name="3.3.6">Function Calls as Statements</a></h3><p> 1723 To allow possible side-effects, 1724 function calls can be executed as statements: 1725 1726 <pre> 1727 stat ::= functioncall 1728 </pre><p> 1729 In this case, all returned values are thrown away. 1730 Function calls are explained in <a href="#3.4.10">§3.4.10</a>. 1731 1732 1733 1734 1735 1736 <h3>3.3.7 – <a name="3.3.7">Local Declarations</a></h3><p> 1737 Local variables can be declared anywhere inside a block. 1738 The declaration can include an initial assignment: 1739 1740 <pre> 1741 stat ::= <b>local</b> namelist [‘<b>=</b>’ explist] 1742 </pre><p> 1743 If present, an initial assignment has the same semantics 1744 of a multiple assignment (see <a href="#3.3.3">§3.3.3</a>). 1745 Otherwise, all variables are initialized with <b>nil</b>. 1746 1747 1748 <p> 1749 A chunk is also a block (see <a href="#3.3.2">§3.3.2</a>), 1750 and so local variables can be declared in a chunk outside any explicit block. 1751 1752 1753 <p> 1754 The visibility rules for local variables are explained in <a href="#3.5">§3.5</a>. 1755 1756 1757 1758 1759 1760 1761 1762 <h2>3.4 – <a name="3.4">Expressions</a></h2> 1763 1764 <p> 1765 The basic expressions in Lua are the following: 1766 1767 <pre> 1768 exp ::= prefixexp 1769 exp ::= <b>nil</b> | <b>false</b> | <b>true</b> 1770 exp ::= Numeral 1771 exp ::= LiteralString 1772 exp ::= functiondef 1773 exp ::= tableconstructor 1774 exp ::= ‘<b>...</b>’ 1775 exp ::= exp binop exp 1776 exp ::= unop exp 1777 prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’ 1778 </pre> 1779 1780 <p> 1781 Numerals and literal strings are explained in <a href="#3.1">§3.1</a>; 1782 variables are explained in <a href="#3.2">§3.2</a>; 1783 function definitions are explained in <a href="#3.4.11">§3.4.11</a>; 1784 function calls are explained in <a href="#3.4.10">§3.4.10</a>; 1785 table constructors are explained in <a href="#3.4.9">§3.4.9</a>. 1786 Vararg expressions, 1787 denoted by three dots ('<code>...</code>'), can only be used when 1788 directly inside a vararg function; 1789 they are explained in <a href="#3.4.11">§3.4.11</a>. 1790 1791 1792 <p> 1793 Binary operators comprise arithmetic operators (see <a href="#3.4.1">§3.4.1</a>), 1794 bitwise operators (see <a href="#3.4.2">§3.4.2</a>), 1795 relational operators (see <a href="#3.4.4">§3.4.4</a>), logical operators (see <a href="#3.4.5">§3.4.5</a>), 1796 and the concatenation operator (see <a href="#3.4.6">§3.4.6</a>). 1797 Unary operators comprise the unary minus (see <a href="#3.4.1">§3.4.1</a>), 1798 the unary bitwise NOT (see <a href="#3.4.2">§3.4.2</a>), 1799 the unary logical <b>not</b> (see <a href="#3.4.5">§3.4.5</a>), 1800 and the unary <em>length operator</em> (see <a href="#3.4.7">§3.4.7</a>). 1801 1802 1803 <p> 1804 Both function calls and vararg expressions can result in multiple values. 1805 If a function call is used as a statement (see <a href="#3.3.6">§3.3.6</a>), 1806 then its return list is adjusted to zero elements, 1807 thus discarding all returned values. 1808 If an expression is used as the last (or the only) element 1809 of a list of expressions, 1810 then no adjustment is made 1811 (unless the expression is enclosed in parentheses). 1812 In all other contexts, 1813 Lua adjusts the result list to one element, 1814 either discarding all values except the first one 1815 or adding a single <b>nil</b> if there are no values. 1816 1817 1818 <p> 1819 Here are some examples: 1820 1821 <pre> 1822 f() -- adjusted to 0 results 1823 g(f(), x) -- f() is adjusted to 1 result 1824 g(x, f()) -- g gets x plus all results from f() 1825 a,b,c = f(), x -- f() is adjusted to 1 result (c gets nil) 1826 a,b = ... -- a gets the first vararg argument, b gets 1827 -- the second (both a and b can get nil if there 1828 -- is no corresponding vararg argument) 1829 1830 a,b,c = x, f() -- f() is adjusted to 2 results 1831 a,b,c = f() -- f() is adjusted to 3 results 1832 return f() -- returns all results from f() 1833 return ... -- returns all received vararg arguments 1834 return x,y,f() -- returns x, y, and all results from f() 1835 {f()} -- creates a list with all results from f() 1836 {...} -- creates a list with all vararg arguments 1837 {f(), nil} -- f() is adjusted to 1 result 1838 </pre> 1839 1840 <p> 1841 Any expression enclosed in parentheses always results in only one value. 1842 Thus, 1843 <code>(f(x,y,z))</code> is always a single value, 1844 even if <code>f</code> returns several values. 1845 (The value of <code>(f(x,y,z))</code> is the first value returned by <code>f</code> 1846 or <b>nil</b> if <code>f</code> does not return any values.) 1847 1848 1849 1850 <h3>3.4.1 – <a name="3.4.1">Arithmetic Operators</a></h3><p> 1851 Lua supports the following arithmetic operators: 1852 1853 <ul> 1854 <li><b><code>+</code>: </b>addition</li> 1855 <li><b><code>-</code>: </b>subtraction</li> 1856 <li><b><code>*</code>: </b>multiplication</li> 1857 <li><b><code>/</code>: </b>float division</li> 1858 <li><b><code>//</code>: </b>floor division</li> 1859 <li><b><code>%</code>: </b>modulo</li> 1860 <li><b><code>^</code>: </b>exponentiation</li> 1861 <li><b><code>-</code>: </b>unary minus</li> 1862 </ul> 1863 1864 <p> 1865 With the exception of exponentiation and float division, 1866 the arithmetic operators work as follows: 1867 If both operands are integers, 1868 the operation is performed over integers and the result is an integer. 1869 Otherwise, if both operands are numbers 1870 or strings that can be converted to 1871 numbers (see <a href="#3.4.3">§3.4.3</a>), 1872 then they are converted to floats, 1873 the operation is performed following the usual rules 1874 for floating-point arithmetic 1875 (usually the IEEE 754 standard), 1876 and the result is a float. 1877 1878 1879 <p> 1880 Exponentiation and float division (<code>/</code>) 1881 always convert their operands to floats 1882 and the result is always a float. 1883 Exponentiation uses the ISO C function <code>pow</code>, 1884 so that it works for non-integer exponents too. 1885 1886 1887 <p> 1888 Floor division (<code>//</code>) is a division 1889 that rounds the quotient towards minus infinity, 1890 that is, the floor of the division of its operands. 1891 1892 1893 <p> 1894 Modulo is defined as the remainder of a division 1895 that rounds the quotient towards minus infinity (floor division). 1896 1897 1898 <p> 1899 In case of overflows in integer arithmetic, 1900 all operations <em>wrap around</em>, 1901 according to the usual rules of two-complement arithmetic. 1902 (In other words, 1903 they return the unique representable integer 1904 that is equal modulo <em>2<sup>64</sup></em> to the mathematical result.) 1905 1906 1907 1908 <h3>3.4.2 – <a name="3.4.2">Bitwise Operators</a></h3><p> 1909 Lua supports the following bitwise operators: 1910 1911 <ul> 1912 <li><b><code>&</code>: </b>bitwise AND</li> 1913 <li><b><code>|</code>: </b>bitwise OR</li> 1914 <li><b><code>~</code>: </b>bitwise exclusive OR</li> 1915 <li><b><code>>></code>: </b>right shift</li> 1916 <li><b><code><<</code>: </b>left shift</li> 1917 <li><b><code>~</code>: </b>unary bitwise NOT</li> 1918 </ul> 1919 1920 <p> 1921 All bitwise operations convert its operands to integers 1922 (see <a href="#3.4.3">§3.4.3</a>), 1923 operate on all bits of those integers, 1924 and result in an integer. 1925 1926 1927 <p> 1928 Both right and left shifts fill the vacant bits with zeros. 1929 Negative displacements shift to the other direction; 1930 displacements with absolute values equal to or higher than 1931 the number of bits in an integer 1932 result in zero (as all bits are shifted out). 1933 1934 1935 1936 1937 1938 <h3>3.4.3 – <a name="3.4.3">Coercions and Conversions</a></h3><p> 1939 Lua provides some automatic conversions between some 1940 types and representations at run time. 1941 Bitwise operators always convert float operands to integers. 1942 Exponentiation and float division 1943 always convert integer operands to floats. 1944 All other arithmetic operations applied to mixed numbers 1945 (integers and floats) convert the integer operand to a float; 1946 this is called the <em>usual rule</em>. 1947 The C API also converts both integers to floats and 1948 floats to integers, as needed. 1949 Moreover, string concatenation accepts numbers as arguments, 1950 besides strings. 1951 1952 1953 <p> 1954 Lua also converts strings to numbers, 1955 whenever a number is expected. 1956 1957 1958 <p> 1959 In a conversion from integer to float, 1960 if the integer value has an exact representation as a float, 1961 that is the result. 1962 Otherwise, 1963 the conversion gets the nearest higher or 1964 the nearest lower representable value. 1965 This kind of conversion never fails. 1966 1967 1968 <p> 1969 The conversion from float to integer 1970 checks whether the float has an exact representation as an integer 1971 (that is, the float has an integral value and 1972 it is in the range of integer representation). 1973 If it does, that representation is the result. 1974 Otherwise, the conversion fails. 1975 1976 1977 <p> 1978 The conversion from strings to numbers goes as follows: 1979 First, the string is converted to an integer or a float, 1980 following its syntax and the rules of the Lua lexer. 1981 (The string may have also leading and trailing spaces and a sign.) 1982 Then, the resulting number (float or integer) 1983 is converted to the type (float or integer) required by the context 1984 (e.g., the operation that forced the conversion). 1985 1986 1987 <p> 1988 All conversions from strings to numbers 1989 accept both a dot and the current locale mark 1990 as the radix character. 1991 (The Lua lexer, however, accepts only a dot.) 1992 1993 1994 <p> 1995 The conversion from numbers to strings uses a 1996 non-specified human-readable format. 1997 For complete control over how numbers are converted to strings, 1998 use the <code>format</code> function from the string library 1999 (see <a href="#pdf-string.format"><code>string.format</code></a>). 2000 2001 2002 2003 2004 2005 <h3>3.4.4 – <a name="3.4.4">Relational Operators</a></h3><p> 2006 Lua supports the following relational operators: 2007 2008 <ul> 2009 <li><b><code>==</code>: </b>equality</li> 2010 <li><b><code>~=</code>: </b>inequality</li> 2011 <li><b><code><</code>: </b>less than</li> 2012 <li><b><code>></code>: </b>greater than</li> 2013 <li><b><code><=</code>: </b>less or equal</li> 2014 <li><b><code>>=</code>: </b>greater or equal</li> 2015 </ul><p> 2016 These operators always result in <b>false</b> or <b>true</b>. 2017 2018 2019 <p> 2020 Equality (<code>==</code>) first compares the type of its operands. 2021 If the types are different, then the result is <b>false</b>. 2022 Otherwise, the values of the operands are compared. 2023 Strings are compared in the obvious way. 2024 Numbers are equal if they denote the same mathematical value. 2025 2026 2027 <p> 2028 Tables, userdata, and threads 2029 are compared by reference: 2030 two objects are considered equal only if they are the same object. 2031 Every time you create a new object 2032 (a table, userdata, or thread), 2033 this new object is different from any previously existing object. 2034 A closure is always equal to itself. 2035 Closures with any detectable difference 2036 (different behavior, different definition) are always different. 2037 Closures created at different times but with no detectable differences 2038 may be classified as equal or not 2039 (depending on internal caching details). 2040 2041 2042 <p> 2043 You can change the way that Lua compares tables and userdata 2044 by using the "eq" metamethod (see <a href="#2.4">§2.4</a>). 2045 2046 2047 <p> 2048 Equality comparisons do not convert strings to numbers 2049 or vice versa. 2050 Thus, <code>"0"==0</code> evaluates to <b>false</b>, 2051 and <code>t[0]</code> and <code>t["0"]</code> denote different 2052 entries in a table. 2053 2054 2055 <p> 2056 The operator <code>~=</code> is exactly the negation of equality (<code>==</code>). 2057 2058 2059 <p> 2060 The order operators work as follows. 2061 If both arguments are numbers, 2062 then they are compared according to their mathematical values 2063 (regardless of their subtypes). 2064 Otherwise, if both arguments are strings, 2065 then their values are compared according to the current locale. 2066 Otherwise, Lua tries to call the "lt" or the "le" 2067 metamethod (see <a href="#2.4">§2.4</a>). 2068 A comparison <code>a > b</code> is translated to <code>b < a</code> 2069 and <code>a >= b</code> is translated to <code>b <= a</code>. 2070 2071 2072 <p> 2073 Following the IEEE 754 standard, 2074 NaN is considered neither smaller than, 2075 nor equal to, nor greater than any value (including itself). 2076 2077 2078 2079 2080 2081 <h3>3.4.5 – <a name="3.4.5">Logical Operators</a></h3><p> 2082 The logical operators in Lua are 2083 <b>and</b>, <b>or</b>, and <b>not</b>. 2084 Like the control structures (see <a href="#3.3.4">§3.3.4</a>), 2085 all logical operators consider both <b>false</b> and <b>nil</b> as false 2086 and anything else as true. 2087 2088 2089 <p> 2090 The negation operator <b>not</b> always returns <b>false</b> or <b>true</b>. 2091 The conjunction operator <b>and</b> returns its first argument 2092 if this value is <b>false</b> or <b>nil</b>; 2093 otherwise, <b>and</b> returns its second argument. 2094 The disjunction operator <b>or</b> returns its first argument 2095 if this value is different from <b>nil</b> and <b>false</b>; 2096 otherwise, <b>or</b> returns its second argument. 2097 Both <b>and</b> and <b>or</b> use short-circuit evaluation; 2098 that is, 2099 the second operand is evaluated only if necessary. 2100 Here are some examples: 2101 2102 <pre> 2103 10 or 20 --> 10 2104 10 or error() --> 10 2105 nil or "a" --> "a" 2106 nil and 10 --> nil 2107 false and error() --> false 2108 false and nil --> false 2109 false or nil --> nil 2110 10 and 20 --> 20 2111 </pre><p> 2112 (In this manual, 2113 <code>--></code> indicates the result of the preceding expression.) 2114 2115 2116 2117 2118 2119 <h3>3.4.6 – <a name="3.4.6">Concatenation</a></h3><p> 2120 The string concatenation operator in Lua is 2121 denoted by two dots ('<code>..</code>'). 2122 If both operands are strings or numbers, then they are converted to 2123 strings according to the rules described in <a href="#3.4.3">§3.4.3</a>. 2124 Otherwise, the <code>__concat</code> metamethod is called (see <a href="#2.4">§2.4</a>). 2125 2126 2127 2128 2129 2130 <h3>3.4.7 – <a name="3.4.7">The Length Operator</a></h3> 2131 2132 <p> 2133 The length operator is denoted by the unary prefix operator <code>#</code>. 2134 2135 2136 <p> 2137 The length of a string is its number of bytes 2138 (that is, the usual meaning of string length when each 2139 character is one byte). 2140 2141 2142 <p> 2143 The length operator applied on a table 2144 returns a border in that table. 2145 A <em>border</em> in a table <code>t</code> is any natural number 2146 that satisfies the following condition: 2147 2148 <pre> 2149 (border == 0 or t[border] ~= nil) and t[border + 1] == nil 2150 </pre><p> 2151 In words, 2152 a border is any (natural) index in a table 2153 where a non-nil value is followed by a nil value 2154 (or zero, when index 1 is nil). 2155 2156 2157 <p> 2158 A table with exactly one border is called a <em>sequence</em>. 2159 For instance, the table <code>{10, 20, 30, 40, 50}</code> is a sequence, 2160 as it has only one border (5). 2161 The table <code>{10, 20, 30, nil, 50}</code> has two borders (3 and 5), 2162 and therefore it is not a sequence. 2163 The table <code>{nil, 20, 30, nil, nil, 60, nil}</code> 2164 has three borders (0, 3, and 6), 2165 so it is not a sequence, too. 2166 The table <code>{}</code> is a sequence with border 0. 2167 Note that non-natural keys do not interfere 2168 with whether a table is a sequence. 2169 2170 2171 <p> 2172 When <code>t</code> is a sequence, 2173 <code>#t</code> returns its only border, 2174 which corresponds to the intuitive notion of the length of the sequence. 2175 When <code>t</code> is not a sequence, 2176 <code>#t</code> can return any of its borders. 2177 (The exact one depends on details of 2178 the internal representation of the table, 2179 which in turn can depend on how the table was populated and 2180 the memory addresses of its non-numeric keys.) 2181 2182 2183 <p> 2184 The computation of the length of a table 2185 has a guaranteed worst time of <em>O(log n)</em>, 2186 where <em>n</em> is the largest natural key in the table. 2187 2188 2189 <p> 2190 A program can modify the behavior of the length operator for 2191 any value but strings through the <code>__len</code> metamethod (see <a href="#2.4">§2.4</a>). 2192 2193 2194 2195 2196 2197 <h3>3.4.8 – <a name="3.4.8">Precedence</a></h3><p> 2198 Operator precedence in Lua follows the table below, 2199 from lower to higher priority: 2200 2201 <pre> 2202 or 2203 and 2204 < > <= >= ~= == 2205 | 2206 ~ 2207 & 2208 << >> 2209 .. 2210 + - 2211 * / // % 2212 unary operators (not # - ~) 2213 ^ 2214 </pre><p> 2215 As usual, 2216 you can use parentheses to change the precedences of an expression. 2217 The concatenation ('<code>..</code>') and exponentiation ('<code>^</code>') 2218 operators are right associative. 2219 All other binary operators are left associative. 2220 2221 2222 2223 2224 2225 <h3>3.4.9 – <a name="3.4.9">Table Constructors</a></h3><p> 2226 Table constructors are expressions that create tables. 2227 Every time a constructor is evaluated, a new table is created. 2228 A constructor can be used to create an empty table 2229 or to create a table and initialize some of its fields. 2230 The general syntax for constructors is 2231 2232 <pre> 2233 tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’ 2234 fieldlist ::= field {fieldsep field} [fieldsep] 2235 field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp 2236 fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’ 2237 </pre> 2238 2239 <p> 2240 Each field of the form <code>[exp1] = exp2</code> adds to the new table an entry 2241 with key <code>exp1</code> and value <code>exp2</code>. 2242 A field of the form <code>name = exp</code> is equivalent to 2243 <code>["name"] = exp</code>. 2244 Finally, fields of the form <code>exp</code> are equivalent to 2245 <code>[i] = exp</code>, where <code>i</code> are consecutive integers 2246 starting with 1. 2247 Fields in the other formats do not affect this counting. 2248 For example, 2249 2250 <pre> 2251 a = { [f(1)] = g; "x", "y"; x = 1, f(x), [30] = 23; 45 } 2252 </pre><p> 2253 is equivalent to 2254 2255 <pre> 2256 do 2257 local t = {} 2258 t[f(1)] = g 2259 t[1] = "x" -- 1st exp 2260 t[2] = "y" -- 2nd exp 2261 t.x = 1 -- t["x"] = 1 2262 t[3] = f(x) -- 3rd exp 2263 t[30] = 23 2264 t[4] = 45 -- 4th exp 2265 a = t 2266 end 2267 </pre> 2268 2269 <p> 2270 The order of the assignments in a constructor is undefined. 2271 (This order would be relevant only when there are repeated keys.) 2272 2273 2274 <p> 2275 If the last field in the list has the form <code>exp</code> 2276 and the expression is a function call or a vararg expression, 2277 then all values returned by this expression enter the list consecutively 2278 (see <a href="#3.4.10">§3.4.10</a>). 2279 2280 2281 <p> 2282 The field list can have an optional trailing separator, 2283 as a convenience for machine-generated code. 2284 2285 2286 2287 2288 2289 <h3>3.4.10 – <a name="3.4.10">Function Calls</a></h3><p> 2290 A function call in Lua has the following syntax: 2291 2292 <pre> 2293 functioncall ::= prefixexp args 2294 </pre><p> 2295 In a function call, 2296 first prefixexp and args are evaluated. 2297 If the value of prefixexp has type <em>function</em>, 2298 then this function is called 2299 with the given arguments. 2300 Otherwise, the prefixexp "call" metamethod is called, 2301 having as first argument the value of prefixexp, 2302 followed by the original call arguments 2303 (see <a href="#2.4">§2.4</a>). 2304 2305 2306 <p> 2307 The form 2308 2309 <pre> 2310 functioncall ::= prefixexp ‘<b>:</b>’ Name args 2311 </pre><p> 2312 can be used to call "methods". 2313 A call <code>v:name(<em>args</em>)</code> 2314 is syntactic sugar for <code>v.name(v,<em>args</em>)</code>, 2315 except that <code>v</code> is evaluated only once. 2316 2317 2318 <p> 2319 Arguments have the following syntax: 2320 2321 <pre> 2322 args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ 2323 args ::= tableconstructor 2324 args ::= LiteralString 2325 </pre><p> 2326 All argument expressions are evaluated before the call. 2327 A call of the form <code>f{<em>fields</em>}</code> is 2328 syntactic sugar for <code>f({<em>fields</em>})</code>; 2329 that is, the argument list is a single new table. 2330 A call of the form <code>f'<em>string</em>'</code> 2331 (or <code>f"<em>string</em>"</code> or <code>f[[<em>string</em>]]</code>) 2332 is syntactic sugar for <code>f('<em>string</em>')</code>; 2333 that is, the argument list is a single literal string. 2334 2335 2336 <p> 2337 A call of the form <code>return <em>functioncall</em></code> is called 2338 a <em>tail call</em>. 2339 Lua implements <em>proper tail calls</em> 2340 (or <em>proper tail recursion</em>): 2341 in a tail call, 2342 the called function reuses the stack entry of the calling function. 2343 Therefore, there is no limit on the number of nested tail calls that 2344 a program can execute. 2345 However, a tail call erases any debug information about the 2346 calling function. 2347 Note that a tail call only happens with a particular syntax, 2348 where the <b>return</b> has one single function call as argument; 2349 this syntax makes the calling function return exactly 2350 the returns of the called function. 2351 So, none of the following examples are tail calls: 2352 2353 <pre> 2354 return (f(x)) -- results adjusted to 1 2355 return 2 * f(x) 2356 return x, f(x) -- additional results 2357 f(x); return -- results discarded 2358 return x or f(x) -- results adjusted to 1 2359 </pre> 2360 2361 2362 2363 2364 <h3>3.4.11 – <a name="3.4.11">Function Definitions</a></h3> 2365 2366 <p> 2367 The syntax for function definition is 2368 2369 <pre> 2370 functiondef ::= <b>function</b> funcbody 2371 funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b> 2372 </pre> 2373 2374 <p> 2375 The following syntactic sugar simplifies function definitions: 2376 2377 <pre> 2378 stat ::= <b>function</b> funcname funcbody 2379 stat ::= <b>local</b> <b>function</b> Name funcbody 2380 funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name] 2381 </pre><p> 2382 The statement 2383 2384 <pre> 2385 function f () <em>body</em> end 2386 </pre><p> 2387 translates to 2388 2389 <pre> 2390 f = function () <em>body</em> end 2391 </pre><p> 2392 The statement 2393 2394 <pre> 2395 function t.a.b.c.f () <em>body</em> end 2396 </pre><p> 2397 translates to 2398 2399 <pre> 2400 t.a.b.c.f = function () <em>body</em> end 2401 </pre><p> 2402 The statement 2403 2404 <pre> 2405 local function f () <em>body</em> end 2406 </pre><p> 2407 translates to 2408 2409 <pre> 2410 local f; f = function () <em>body</em> end 2411 </pre><p> 2412 not to 2413 2414 <pre> 2415 local f = function () <em>body</em> end 2416 </pre><p> 2417 (This only makes a difference when the body of the function 2418 contains references to <code>f</code>.) 2419 2420 2421 <p> 2422 A function definition is an executable expression, 2423 whose value has type <em>function</em>. 2424 When Lua precompiles a chunk, 2425 all its function bodies are precompiled too. 2426 Then, whenever Lua executes the function definition, 2427 the function is <em>instantiated</em> (or <em>closed</em>). 2428 This function instance (or <em>closure</em>) 2429 is the final value of the expression. 2430 2431 2432 <p> 2433 Parameters act as local variables that are 2434 initialized with the argument values: 2435 2436 <pre> 2437 parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’ 2438 </pre><p> 2439 When a function is called, 2440 the list of arguments is adjusted to 2441 the length of the list of parameters, 2442 unless the function is a <em>vararg function</em>, 2443 which is indicated by three dots ('<code>...</code>') 2444 at the end of its parameter list. 2445 A vararg function does not adjust its argument list; 2446 instead, it collects all extra arguments and supplies them 2447 to the function through a <em>vararg expression</em>, 2448 which is also written as three dots. 2449 The value of this expression is a list of all actual extra arguments, 2450 similar to a function with multiple results. 2451 If a vararg expression is used inside another expression 2452 or in the middle of a list of expressions, 2453 then its return list is adjusted to one element. 2454 If the expression is used as the last element of a list of expressions, 2455 then no adjustment is made 2456 (unless that last expression is enclosed in parentheses). 2457 2458 2459 <p> 2460 As an example, consider the following definitions: 2461 2462 <pre> 2463 function f(a, b) end 2464 function g(a, b, ...) end 2465 function r() return 1,2,3 end 2466 </pre><p> 2467 Then, we have the following mapping from arguments to parameters and 2468 to the vararg expression: 2469 2470 <pre> 2471 CALL PARAMETERS 2472 2473 f(3) a=3, b=nil 2474 f(3, 4) a=3, b=4 2475 f(3, 4, 5) a=3, b=4 2476 f(r(), 10) a=1, b=10 2477 f(r()) a=1, b=2 2478 2479 g(3) a=3, b=nil, ... --> (nothing) 2480 g(3, 4) a=3, b=4, ... --> (nothing) 2481 g(3, 4, 5, 8) a=3, b=4, ... --> 5 8 2482 g(5, r()) a=5, b=1, ... --> 2 3 2483 </pre> 2484 2485 <p> 2486 Results are returned using the <b>return</b> statement (see <a href="#3.3.4">§3.3.4</a>). 2487 If control reaches the end of a function 2488 without encountering a <b>return</b> statement, 2489 then the function returns with no results. 2490 2491 2492 <p> 2493 2494 There is a system-dependent limit on the number of values 2495 that a function may return. 2496 This limit is guaranteed to be larger than 1000. 2497 2498 2499 <p> 2500 The <em>colon</em> syntax 2501 is used for defining <em>methods</em>, 2502 that is, functions that have an implicit extra parameter <code>self</code>. 2503 Thus, the statement 2504 2505 <pre> 2506 function t.a.b.c:f (<em>params</em>) <em>body</em> end 2507 </pre><p> 2508 is syntactic sugar for 2509 2510 <pre> 2511 t.a.b.c.f = function (self, <em>params</em>) <em>body</em> end 2512 </pre> 2513 2514 2515 2516 2517 2518 2519 <h2>3.5 – <a name="3.5">Visibility Rules</a></h2> 2520 2521 <p> 2522 2523 Lua is a lexically scoped language. 2524 The scope of a local variable begins at the first statement after 2525 its declaration and lasts until the last non-void statement 2526 of the innermost block that includes the declaration. 2527 Consider the following example: 2528 2529 <pre> 2530 x = 10 -- global variable 2531 do -- new block 2532 local x = x -- new 'x', with value 10 2533 print(x) --> 10 2534 x = x+1 2535 do -- another block 2536 local x = x+1 -- another 'x' 2537 print(x) --> 12 2538 end 2539 print(x) --> 11 2540 end 2541 print(x) --> 10 (the global one) 2542 </pre> 2543 2544 <p> 2545 Notice that, in a declaration like <code>local x = x</code>, 2546 the new <code>x</code> being declared is not in scope yet, 2547 and so the second <code>x</code> refers to the outside variable. 2548 2549 2550 <p> 2551 Because of the lexical scoping rules, 2552 local variables can be freely accessed by functions 2553 defined inside their scope. 2554 A local variable used by an inner function is called 2555 an <em>upvalue</em>, or <em>external local variable</em>, 2556 inside the inner function. 2557 2558 2559 <p> 2560 Notice that each execution of a <b>local</b> statement 2561 defines new local variables. 2562 Consider the following example: 2563 2564 <pre> 2565 a = {} 2566 local x = 20 2567 for i=1,10 do 2568 local y = 0 2569 a[i] = function () y=y+1; return x+y end 2570 end 2571 </pre><p> 2572 The loop creates ten closures 2573 (that is, ten instances of the anonymous function). 2574 Each of these closures uses a different <code>y</code> variable, 2575 while all of them share the same <code>x</code>. 2576 2577 2578 2579 2580 2581 <h1>4 – <a name="4">The Application Program Interface</a></h1> 2582 2583 <p> 2584 2585 This section describes the C API for Lua, that is, 2586 the set of C functions available to the host program to communicate 2587 with Lua. 2588 All API functions and related types and constants 2589 are declared in the header file <a name="pdf-lua.h"><code>lua.h</code></a>. 2590 2591 2592 <p> 2593 Even when we use the term "function", 2594 any facility in the API may be provided as a macro instead. 2595 Except where stated otherwise, 2596 all such macros use each of their arguments exactly once 2597 (except for the first argument, which is always a Lua state), 2598 and so do not generate any hidden side-effects. 2599 2600 2601 <p> 2602 As in most C libraries, 2603 the Lua API functions do not check their arguments for validity or consistency. 2604 However, you can change this behavior by compiling Lua 2605 with the macro <a name="pdf-LUA_USE_APICHECK"><code>LUA_USE_APICHECK</code></a> defined. 2606 2607 2608 <p> 2609 The Lua library is fully reentrant: 2610 it has no global variables. 2611 It keeps all information it needs in a dynamic structure, 2612 called the <em>Lua state</em>. 2613 2614 2615 <p> 2616 Each Lua state has one or more threads, 2617 which correspond to independent, cooperative lines of execution. 2618 The type <a href="#lua_State"><code>lua_State</code></a> (despite its name) refers to a thread. 2619 (Indirectly, through the thread, it also refers to the 2620 Lua state associated to the thread.) 2621 2622 2623 <p> 2624 A pointer to a thread must be passed as the first argument to 2625 every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>, 2626 which creates a Lua state from scratch and returns a pointer 2627 to the <em>main thread</em> in the new state. 2628 2629 2630 2631 <h2>4.1 – <a name="4.1">The Stack</a></h2> 2632 2633 <p> 2634 Lua uses a <em>virtual stack</em> to pass values to and from C. 2635 Each element in this stack represents a Lua value 2636 (<b>nil</b>, number, string, etc.). 2637 Functions in the API can access this stack through the 2638 Lua state parameter that they receive. 2639 2640 2641 <p> 2642 Whenever Lua calls C, the called function gets a new stack, 2643 which is independent of previous stacks and of stacks of 2644 C functions that are still active. 2645 This stack initially contains any arguments to the C function 2646 and it is where the C function can store temporary 2647 Lua values and must push its results 2648 to be returned to the caller (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). 2649 2650 2651 <p> 2652 For convenience, 2653 most query operations in the API do not follow a strict stack discipline. 2654 Instead, they can refer to any element in the stack 2655 by using an <em>index</em>: 2656 A positive index represents an absolute stack position 2657 (starting at 1); 2658 a negative index represents an offset relative to the top of the stack. 2659 More specifically, if the stack has <em>n</em> elements, 2660 then index 1 represents the first element 2661 (that is, the element that was pushed onto the stack first) 2662 and 2663 index <em>n</em> represents the last element; 2664 index -1 also represents the last element 2665 (that is, the element at the top) 2666 and index <em>-n</em> represents the first element. 2667 2668 2669 2670 2671 2672 <h2>4.2 – <a name="4.2">Stack Size</a></h2> 2673 2674 <p> 2675 When you interact with the Lua API, 2676 you are responsible for ensuring consistency. 2677 In particular, 2678 <em>you are responsible for controlling stack overflow</em>. 2679 You can use the function <a href="#lua_checkstack"><code>lua_checkstack</code></a> 2680 to ensure that the stack has enough space for pushing new elements. 2681 2682 2683 <p> 2684 Whenever Lua calls C, 2685 it ensures that the stack has space for 2686 at least <a name="pdf-LUA_MINSTACK"><code>LUA_MINSTACK</code></a> extra slots. 2687 <code>LUA_MINSTACK</code> is defined as 20, 2688 so that usually you do not have to worry about stack space 2689 unless your code has loops pushing elements onto the stack. 2690 2691 2692 <p> 2693 When you call a Lua function 2694 without a fixed number of results (see <a href="#lua_call"><code>lua_call</code></a>), 2695 Lua ensures that the stack has enough space for all results, 2696 but it does not ensure any extra space. 2697 So, before pushing anything in the stack after such a call 2698 you should use <a href="#lua_checkstack"><code>lua_checkstack</code></a>. 2699 2700 2701 2702 2703 2704 <h2>4.3 – <a name="4.3">Valid and Acceptable Indices</a></h2> 2705 2706 <p> 2707 Any function in the API that receives stack indices 2708 works only with <em>valid indices</em> or <em>acceptable indices</em>. 2709 2710 2711 <p> 2712 A <em>valid index</em> is an index that refers to a 2713 position that stores a modifiable Lua value. 2714 It comprises stack indices between 1 and the stack top 2715 (<code>1 ≤ abs(index) ≤ top</code>) 2716 2717 plus <em>pseudo-indices</em>, 2718 which represent some positions that are accessible to C code 2719 but that are not in the stack. 2720 Pseudo-indices are used to access the registry (see <a href="#4.5">§4.5</a>) 2721 and the upvalues of a C function (see <a href="#4.4">§4.4</a>). 2722 2723 2724 <p> 2725 Functions that do not need a specific mutable position, 2726 but only a value (e.g., query functions), 2727 can be called with acceptable indices. 2728 An <em>acceptable index</em> can be any valid index, 2729 but it also can be any positive index after the stack top 2730 within the space allocated for the stack, 2731 that is, indices up to the stack size. 2732 (Note that 0 is never an acceptable index.) 2733 Except when noted otherwise, 2734 functions in the API work with acceptable indices. 2735 2736 2737 <p> 2738 Acceptable indices serve to avoid extra tests 2739 against the stack top when querying the stack. 2740 For instance, a C function can query its third argument 2741 without the need to first check whether there is a third argument, 2742 that is, without the need to check whether 3 is a valid index. 2743 2744 2745 <p> 2746 For functions that can be called with acceptable indices, 2747 any non-valid index is treated as if it 2748 contains a value of a virtual type <a name="pdf-LUA_TNONE"><code>LUA_TNONE</code></a>, 2749 which behaves like a nil value. 2750 2751 2752 2753 2754 2755 <h2>4.4 – <a name="4.4">C Closures</a></h2> 2756 2757 <p> 2758 When a C function is created, 2759 it is possible to associate some values with it, 2760 thus creating a <em>C closure</em> 2761 (see <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a>); 2762 these values are called <em>upvalues</em> and are 2763 accessible to the function whenever it is called. 2764 2765 2766 <p> 2767 Whenever a C function is called, 2768 its upvalues are located at specific pseudo-indices. 2769 These pseudo-indices are produced by the macro 2770 <a href="#lua_upvalueindex"><code>lua_upvalueindex</code></a>. 2771 The first upvalue associated with a function is at index 2772 <code>lua_upvalueindex(1)</code>, and so on. 2773 Any access to <code>lua_upvalueindex(<em>n</em>)</code>, 2774 where <em>n</em> is greater than the number of upvalues of the 2775 current function 2776 (but not greater than 256, 2777 which is one plus the maximum number of upvalues in a closure), 2778 produces an acceptable but invalid index. 2779 2780 2781 2782 2783 2784 <h2>4.5 – <a name="4.5">Registry</a></h2> 2785 2786 <p> 2787 Lua provides a <em>registry</em>, 2788 a predefined table that can be used by any C code to 2789 store whatever Lua values it needs to store. 2790 The registry table is always located at pseudo-index 2791 <a name="pdf-LUA_REGISTRYINDEX"><code>LUA_REGISTRYINDEX</code></a>. 2792 Any C library can store data into this table, 2793 but it must take care to choose keys 2794 that are different from those used 2795 by other libraries, to avoid collisions. 2796 Typically, you should use as key a string containing your library name, 2797 or a light userdata with the address of a C object in your code, 2798 or any Lua object created by your code. 2799 As with variable names, 2800 string keys starting with an underscore followed by 2801 uppercase letters are reserved for Lua. 2802 2803 2804 <p> 2805 The integer keys in the registry are used 2806 by the reference mechanism (see <a href="#luaL_ref"><code>luaL_ref</code></a>) 2807 and by some predefined values. 2808 Therefore, integer keys must not be used for other purposes. 2809 2810 2811 <p> 2812 When you create a new Lua state, 2813 its registry comes with some predefined values. 2814 These predefined values are indexed with integer keys 2815 defined as constants in <code>lua.h</code>. 2816 The following constants are defined: 2817 2818 <ul> 2819 <li><b><a name="pdf-LUA_RIDX_MAINTHREAD"><code>LUA_RIDX_MAINTHREAD</code></a>: </b> At this index the registry has 2820 the main thread of the state. 2821 (The main thread is the one created together with the state.) 2822 </li> 2823 2824 <li><b><a name="pdf-LUA_RIDX_GLOBALS"><code>LUA_RIDX_GLOBALS</code></a>: </b> At this index the registry has 2825 the global environment. 2826 </li> 2827 </ul> 2828 2829 2830 2831 2832 <h2>4.6 – <a name="4.6">Error Handling in C</a></h2> 2833 2834 <p> 2835 Internally, Lua uses the C <code>longjmp</code> facility to handle errors. 2836 (Lua will use exceptions if you compile it as C++; 2837 search for <code>LUAI_THROW</code> in the source code for details.) 2838 When Lua faces any error 2839 (such as a memory allocation error or a type error) 2840 it <em>raises</em> an error; 2841 that is, it does a long jump. 2842 A <em>protected environment</em> uses <code>setjmp</code> 2843 to set a recovery point; 2844 any error jumps to the most recent active recovery point. 2845 2846 2847 <p> 2848 Inside a C function you can raise an error by calling <a href="#lua_error"><code>lua_error</code></a>. 2849 2850 2851 <p> 2852 Most functions in the API can raise an error, 2853 for instance due to a memory allocation error. 2854 The documentation for each function indicates whether 2855 it can raise errors. 2856 2857 2858 <p> 2859 If an error happens outside any protected environment, 2860 Lua calls a <em>panic function</em> (see <a href="#lua_atpanic"><code>lua_atpanic</code></a>) 2861 and then calls <code>abort</code>, 2862 thus exiting the host application. 2863 Your panic function can avoid this exit by 2864 never returning 2865 (e.g., doing a long jump to your own recovery point outside Lua). 2866 2867 2868 <p> 2869 The panic function, 2870 as its name implies, 2871 is a mechanism of last resort. 2872 Programs should avoid it. 2873 As a general rule, 2874 when a C function is called by Lua with a Lua state, 2875 it can do whatever it wants on that Lua state, 2876 as it should be already protected. 2877 However, 2878 when C code operates on other Lua states 2879 (e.g., a Lua argument to the function, 2880 a Lua state stored in the registry, or 2881 the result of <a href="#lua_newthread"><code>lua_newthread</code></a>), 2882 it should use them only in API calls that cannot raise errors. 2883 2884 2885 <p> 2886 The panic function runs as if it were a message handler (see <a href="#2.3">§2.3</a>); 2887 in particular, the error object is at the top of the stack. 2888 However, there is no guarantee about stack space. 2889 To push anything on the stack, 2890 the panic function must first check the available space (see <a href="#4.2">§4.2</a>). 2891 2892 2893 2894 2895 2896 <h2>4.7 – <a name="4.7">Handling Yields in C</a></h2> 2897 2898 <p> 2899 Internally, Lua uses the C <code>longjmp</code> facility to yield a coroutine. 2900 Therefore, if a C function <code>foo</code> calls an API function 2901 and this API function yields 2902 (directly or indirectly by calling another function that yields), 2903 Lua cannot return to <code>foo</code> any more, 2904 because the <code>longjmp</code> removes its frame from the C stack. 2905 2906 2907 <p> 2908 To avoid this kind of problem, 2909 Lua raises an error whenever it tries to yield across an API call, 2910 except for three functions: 2911 <a href="#lua_yieldk"><code>lua_yieldk</code></a>, <a href="#lua_callk"><code>lua_callk</code></a>, and <a href="#lua_pcallk"><code>lua_pcallk</code></a>. 2912 All those functions receive a <em>continuation function</em> 2913 (as a parameter named <code>k</code>) to continue execution after a yield. 2914 2915 2916 <p> 2917 We need to set some terminology to explain continuations. 2918 We have a C function called from Lua which we will call 2919 the <em>original function</em>. 2920 This original function then calls one of those three functions in the C API, 2921 which we will call the <em>callee function</em>, 2922 that then yields the current thread. 2923 (This can happen when the callee function is <a href="#lua_yieldk"><code>lua_yieldk</code></a>, 2924 or when the callee function is either <a href="#lua_callk"><code>lua_callk</code></a> or <a href="#lua_pcallk"><code>lua_pcallk</code></a> 2925 and the function called by them yields.) 2926 2927 2928 <p> 2929 Suppose the running thread yields while executing the callee function. 2930 After the thread resumes, 2931 it eventually will finish running the callee function. 2932 However, 2933 the callee function cannot return to the original function, 2934 because its frame in the C stack was destroyed by the yield. 2935 Instead, Lua calls a <em>continuation function</em>, 2936 which was given as an argument to the callee function. 2937 As the name implies, 2938 the continuation function should continue the task 2939 of the original function. 2940 2941 2942 <p> 2943 As an illustration, consider the following function: 2944 2945 <pre> 2946 int original_function (lua_State *L) { 2947 ... /* code 1 */ 2948 status = lua_pcall(L, n, m, h); /* calls Lua */ 2949 ... /* code 2 */ 2950 } 2951 </pre><p> 2952 Now we want to allow 2953 the Lua code being run by <a href="#lua_pcall"><code>lua_pcall</code></a> to yield. 2954 First, we can rewrite our function like here: 2955 2956 <pre> 2957 int k (lua_State *L, int status, lua_KContext ctx) { 2958 ... /* code 2 */ 2959 } 2960 2961 int original_function (lua_State *L) { 2962 ... /* code 1 */ 2963 return k(L, lua_pcall(L, n, m, h), ctx); 2964 } 2965 </pre><p> 2966 In the above code, 2967 the new function <code>k</code> is a 2968 <em>continuation function</em> (with type <a href="#lua_KFunction"><code>lua_KFunction</code></a>), 2969 which should do all the work that the original function 2970 was doing after calling <a href="#lua_pcall"><code>lua_pcall</code></a>. 2971 Now, we must inform Lua that it must call <code>k</code> if the Lua code 2972 being executed by <a href="#lua_pcall"><code>lua_pcall</code></a> gets interrupted in some way 2973 (errors or yielding), 2974 so we rewrite the code as here, 2975 replacing <a href="#lua_pcall"><code>lua_pcall</code></a> by <a href="#lua_pcallk"><code>lua_pcallk</code></a>: 2976 2977 <pre> 2978 int original_function (lua_State *L) { 2979 ... /* code 1 */ 2980 return k(L, lua_pcallk(L, n, m, h, ctx2, k), ctx1); 2981 } 2982 </pre><p> 2983 Note the external, explicit call to the continuation: 2984 Lua will call the continuation only if needed, that is, 2985 in case of errors or resuming after a yield. 2986 If the called function returns normally without ever yielding, 2987 <a href="#lua_pcallk"><code>lua_pcallk</code></a> (and <a href="#lua_callk"><code>lua_callk</code></a>) will also return normally. 2988 (Of course, instead of calling the continuation in that case, 2989 you can do the equivalent work directly inside the original function.) 2990 2991 2992 <p> 2993 Besides the Lua state, 2994 the continuation function has two other parameters: 2995 the final status of the call plus the context value (<code>ctx</code>) that 2996 was passed originally to <a href="#lua_pcallk"><code>lua_pcallk</code></a>. 2997 (Lua does not use this context value; 2998 it only passes this value from the original function to the 2999 continuation function.) 3000 For <a href="#lua_pcallk"><code>lua_pcallk</code></a>, 3001 the status is the same value that would be returned by <a href="#lua_pcallk"><code>lua_pcallk</code></a>, 3002 except that it is <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when being executed after a yield 3003 (instead of <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>). 3004 For <a href="#lua_yieldk"><code>lua_yieldk</code></a> and <a href="#lua_callk"><code>lua_callk</code></a>, 3005 the status is always <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> when Lua calls the continuation. 3006 (For these two functions, 3007 Lua will not call the continuation in case of errors, 3008 because they do not handle errors.) 3009 Similarly, when using <a href="#lua_callk"><code>lua_callk</code></a>, 3010 you should call the continuation function 3011 with <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> as the status. 3012 (For <a href="#lua_yieldk"><code>lua_yieldk</code></a>, there is not much point in calling 3013 directly the continuation function, 3014 because <a href="#lua_yieldk"><code>lua_yieldk</code></a> usually does not return.) 3015 3016 3017 <p> 3018 Lua treats the continuation function as if it were the original function. 3019 The continuation function receives the same Lua stack 3020 from the original function, 3021 in the same state it would be if the callee function had returned. 3022 (For instance, 3023 after a <a href="#lua_callk"><code>lua_callk</code></a> the function and its arguments are 3024 removed from the stack and replaced by the results from the call.) 3025 It also has the same upvalues. 3026 Whatever it returns is handled by Lua as if it were the return 3027 of the original function. 3028 3029 3030 3031 3032 3033 <h2>4.8 – <a name="4.8">Functions and Types</a></h2> 3034 3035 <p> 3036 Here we list all functions and types from the C API in 3037 alphabetical order. 3038 Each function has an indicator like this: 3039 <span class="apii">[-o, +p, <em>x</em>]</span> 3040 3041 3042 <p> 3043 The first field, <code>o</code>, 3044 is how many elements the function pops from the stack. 3045 The second field, <code>p</code>, 3046 is how many elements the function pushes onto the stack. 3047 (Any function always pushes its results after popping its arguments.) 3048 A field in the form <code>x|y</code> means the function can push (or pop) 3049 <code>x</code> or <code>y</code> elements, 3050 depending on the situation; 3051 an interrogation mark '<code>?</code>' means that 3052 we cannot know how many elements the function pops/pushes 3053 by looking only at its arguments 3054 (e.g., they may depend on what is on the stack). 3055 The third field, <code>x</code>, 3056 tells whether the function may raise errors: 3057 '<code>-</code>' means the function never raises any error; 3058 '<code>m</code>' means the function may raise out-of-memory errors 3059 and errors running a <code>__gc</code> metamethod; 3060 '<code>e</code>' means the function may raise any errors 3061 (it can run arbitrary Lua code, 3062 either directly or through metamethods); 3063 '<code>v</code>' means the function may raise an error on purpose. 3064 3065 3066 3067 <hr><h3><a name="lua_absindex"><code>lua_absindex</code></a></h3><p> 3068 <span class="apii">[-0, +0, –]</span> 3069 <pre>int lua_absindex (lua_State *L, int idx);</pre> 3070 3071 <p> 3072 Converts the acceptable index <code>idx</code> 3073 into an equivalent absolute index 3074 (that is, one that does not depend on the stack top). 3075 3076 3077 3078 3079 3080 <hr><h3><a name="lua_Alloc"><code>lua_Alloc</code></a></h3> 3081 <pre>typedef void * (*lua_Alloc) (void *ud, 3082 void *ptr, 3083 size_t osize, 3084 size_t nsize);</pre> 3085 3086 <p> 3087 The type of the memory-allocation function used by Lua states. 3088 The allocator function must provide a 3089 functionality similar to <code>realloc</code>, 3090 but not exactly the same. 3091 Its arguments are 3092 <code>ud</code>, an opaque pointer passed to <a href="#lua_newstate"><code>lua_newstate</code></a>; 3093 <code>ptr</code>, a pointer to the block being allocated/reallocated/freed; 3094 <code>osize</code>, the original size of the block or some code about what 3095 is being allocated; 3096 and <code>nsize</code>, the new size of the block. 3097 3098 3099 <p> 3100 When <code>ptr</code> is not <code>NULL</code>, 3101 <code>osize</code> is the size of the block pointed by <code>ptr</code>, 3102 that is, the size given when it was allocated or reallocated. 3103 3104 3105 <p> 3106 When <code>ptr</code> is <code>NULL</code>, 3107 <code>osize</code> encodes the kind of object that Lua is allocating. 3108 <code>osize</code> is any of 3109 <a href="#pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, <a href="#pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, <a href="#pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>, 3110 <a href="#pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, or <a href="#pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a> when (and only when) 3111 Lua is creating a new object of that type. 3112 When <code>osize</code> is some other value, 3113 Lua is allocating memory for something else. 3114 3115 3116 <p> 3117 Lua assumes the following behavior from the allocator function: 3118 3119 3120 <p> 3121 When <code>nsize</code> is zero, 3122 the allocator must behave like <code>free</code> 3123 and return <code>NULL</code>. 3124 3125 3126 <p> 3127 When <code>nsize</code> is not zero, 3128 the allocator must behave like <code>realloc</code>. 3129 The allocator returns <code>NULL</code> 3130 if and only if it cannot fulfill the request. 3131 Lua assumes that the allocator never fails when 3132 <code>osize >= nsize</code>. 3133 3134 3135 <p> 3136 Here is a simple implementation for the allocator function. 3137 It is used in the auxiliary library by <a href="#luaL_newstate"><code>luaL_newstate</code></a>. 3138 3139 <pre> 3140 static void *l_alloc (void *ud, void *ptr, size_t osize, 3141 size_t nsize) { 3142 (void)ud; (void)osize; /* not used */ 3143 if (nsize == 0) { 3144 free(ptr); 3145 return NULL; 3146 } 3147 else 3148 return realloc(ptr, nsize); 3149 } 3150 </pre><p> 3151 Note that Standard C ensures 3152 that <code>free(NULL)</code> has no effect and that 3153 <code>realloc(NULL,size)</code> is equivalent to <code>malloc(size)</code>. 3154 This code assumes that <code>realloc</code> does not fail when shrinking a block. 3155 (Although Standard C does not ensure this behavior, 3156 it seems to be a safe assumption.) 3157 3158 3159 3160 3161 3162 <hr><h3><a name="lua_arith"><code>lua_arith</code></a></h3><p> 3163 <span class="apii">[-(2|1), +1, <em>e</em>]</span> 3164 <pre>void lua_arith (lua_State *L, int op);</pre> 3165 3166 <p> 3167 Performs an arithmetic or bitwise operation over the two values 3168 (or one, in the case of negations) 3169 at the top of the stack, 3170 with the value at the top being the second operand, 3171 pops these values, and pushes the result of the operation. 3172 The function follows the semantics of the corresponding Lua operator 3173 (that is, it may call metamethods). 3174 3175 3176 <p> 3177 The value of <code>op</code> must be one of the following constants: 3178 3179 <ul> 3180 3181 <li><b><a name="pdf-LUA_OPADD"><code>LUA_OPADD</code></a>: </b> performs addition (<code>+</code>)</li> 3182 <li><b><a name="pdf-LUA_OPSUB"><code>LUA_OPSUB</code></a>: </b> performs subtraction (<code>-</code>)</li> 3183 <li><b><a name="pdf-LUA_OPMUL"><code>LUA_OPMUL</code></a>: </b> performs multiplication (<code>*</code>)</li> 3184 <li><b><a name="pdf-LUA_OPDIV"><code>LUA_OPDIV</code></a>: </b> performs float division (<code>/</code>)</li> 3185 <li><b><a name="pdf-LUA_OPIDIV"><code>LUA_OPIDIV</code></a>: </b> performs floor division (<code>//</code>)</li> 3186 <li><b><a name="pdf-LUA_OPMOD"><code>LUA_OPMOD</code></a>: </b> performs modulo (<code>%</code>)</li> 3187 <li><b><a name="pdf-LUA_OPPOW"><code>LUA_OPPOW</code></a>: </b> performs exponentiation (<code>^</code>)</li> 3188 <li><b><a name="pdf-LUA_OPUNM"><code>LUA_OPUNM</code></a>: </b> performs mathematical negation (unary <code>-</code>)</li> 3189 <li><b><a name="pdf-LUA_OPBNOT"><code>LUA_OPBNOT</code></a>: </b> performs bitwise NOT (<code>~</code>)</li> 3190 <li><b><a name="pdf-LUA_OPBAND"><code>LUA_OPBAND</code></a>: </b> performs bitwise AND (<code>&</code>)</li> 3191 <li><b><a name="pdf-LUA_OPBOR"><code>LUA_OPBOR</code></a>: </b> performs bitwise OR (<code>|</code>)</li> 3192 <li><b><a name="pdf-LUA_OPBXOR"><code>LUA_OPBXOR</code></a>: </b> performs bitwise exclusive OR (<code>~</code>)</li> 3193 <li><b><a name="pdf-LUA_OPSHL"><code>LUA_OPSHL</code></a>: </b> performs left shift (<code><<</code>)</li> 3194 <li><b><a name="pdf-LUA_OPSHR"><code>LUA_OPSHR</code></a>: </b> performs right shift (<code>>></code>)</li> 3195 3196 </ul> 3197 3198 3199 3200 3201 <hr><h3><a name="lua_atpanic"><code>lua_atpanic</code></a></h3><p> 3202 <span class="apii">[-0, +0, –]</span> 3203 <pre>lua_CFunction lua_atpanic (lua_State *L, lua_CFunction panicf);</pre> 3204 3205 <p> 3206 Sets a new panic function and returns the old one (see <a href="#4.6">§4.6</a>). 3207 3208 3209 3210 3211 3212 <hr><h3><a name="lua_call"><code>lua_call</code></a></h3><p> 3213 <span class="apii">[-(nargs+1), +nresults, <em>e</em>]</span> 3214 <pre>void lua_call (lua_State *L, int nargs, int nresults);</pre> 3215 3216 <p> 3217 Calls a function. 3218 3219 3220 <p> 3221 To call a function you must use the following protocol: 3222 first, the function to be called is pushed onto the stack; 3223 then, the arguments to the function are pushed 3224 in direct order; 3225 that is, the first argument is pushed first. 3226 Finally you call <a href="#lua_call"><code>lua_call</code></a>; 3227 <code>nargs</code> is the number of arguments that you pushed onto the stack. 3228 All arguments and the function value are popped from the stack 3229 when the function is called. 3230 The function results are pushed onto the stack when the function returns. 3231 The number of results is adjusted to <code>nresults</code>, 3232 unless <code>nresults</code> is <a name="pdf-LUA_MULTRET"><code>LUA_MULTRET</code></a>. 3233 In this case, all results from the function are pushed; 3234 Lua takes care that the returned values fit into the stack space, 3235 but it does not ensure any extra space in the stack. 3236 The function results are pushed onto the stack in direct order 3237 (the first result is pushed first), 3238 so that after the call the last result is on the top of the stack. 3239 3240 3241 <p> 3242 Any error inside the called function is propagated upwards 3243 (with a <code>longjmp</code>). 3244 3245 3246 <p> 3247 The following example shows how the host program can do the 3248 equivalent to this Lua code: 3249 3250 <pre> 3251 a = f("how", t.x, 14) 3252 </pre><p> 3253 Here it is in C: 3254 3255 <pre> 3256 lua_getglobal(L, "f"); /* function to be called */ 3257 lua_pushliteral(L, "how"); /* 1st argument */ 3258 lua_getglobal(L, "t"); /* table to be indexed */ 3259 lua_getfield(L, -1, "x"); /* push result of t.x (2nd arg) */ 3260 lua_remove(L, -2); /* remove 't' from the stack */ 3261 lua_pushinteger(L, 14); /* 3rd argument */ 3262 lua_call(L, 3, 1); /* call 'f' with 3 arguments and 1 result */ 3263 lua_setglobal(L, "a"); /* set global 'a' */ 3264 </pre><p> 3265 Note that the code above is <em>balanced</em>: 3266 at its end, the stack is back to its original configuration. 3267 This is considered good programming practice. 3268 3269 3270 3271 3272 3273 <hr><h3><a name="lua_callk"><code>lua_callk</code></a></h3><p> 3274 <span class="apii">[-(nargs + 1), +nresults, <em>e</em>]</span> 3275 <pre>void lua_callk (lua_State *L, 3276 int nargs, 3277 int nresults, 3278 lua_KContext ctx, 3279 lua_KFunction k);</pre> 3280 3281 <p> 3282 This function behaves exactly like <a href="#lua_call"><code>lua_call</code></a>, 3283 but allows the called function to yield (see <a href="#4.7">§4.7</a>). 3284 3285 3286 3287 3288 3289 <hr><h3><a name="lua_CFunction"><code>lua_CFunction</code></a></h3> 3290 <pre>typedef int (*lua_CFunction) (lua_State *L);</pre> 3291 3292 <p> 3293 Type for C functions. 3294 3295 3296 <p> 3297 In order to communicate properly with Lua, 3298 a C function must use the following protocol, 3299 which defines the way parameters and results are passed: 3300 a C function receives its arguments from Lua in its stack 3301 in direct order (the first argument is pushed first). 3302 So, when the function starts, 3303 <code>lua_gettop(L)</code> returns the number of arguments received by the function. 3304 The first argument (if any) is at index 1 3305 and its last argument is at index <code>lua_gettop(L)</code>. 3306 To return values to Lua, a C function just pushes them onto the stack, 3307 in direct order (the first result is pushed first), 3308 and returns the number of results. 3309 Any other value in the stack below the results will be properly 3310 discarded by Lua. 3311 Like a Lua function, a C function called by Lua can also return 3312 many results. 3313 3314 3315 <p> 3316 As an example, the following function receives a variable number 3317 of numeric arguments and returns their average and their sum: 3318 3319 <pre> 3320 static int foo (lua_State *L) { 3321 int n = lua_gettop(L); /* number of arguments */ 3322 lua_Number sum = 0.0; 3323 int i; 3324 for (i = 1; i <= n; i++) { 3325 if (!lua_isnumber(L, i)) { 3326 lua_pushliteral(L, "incorrect argument"); 3327 lua_error(L); 3328 } 3329 sum += lua_tonumber(L, i); 3330 } 3331 lua_pushnumber(L, sum/n); /* first result */ 3332 lua_pushnumber(L, sum); /* second result */ 3333 return 2; /* number of results */ 3334 } 3335 </pre> 3336 3337 3338 3339 3340 <hr><h3><a name="lua_checkstack"><code>lua_checkstack</code></a></h3><p> 3341 <span class="apii">[-0, +0, –]</span> 3342 <pre>int lua_checkstack (lua_State *L, int n);</pre> 3343 3344 <p> 3345 Ensures that the stack has space for at least <code>n</code> extra slots 3346 (that is, that you can safely push up to <code>n</code> values into it). 3347 It returns false if it cannot fulfill the request, 3348 either because it would cause the stack 3349 to be larger than a fixed maximum size 3350 (typically at least several thousand elements) or 3351 because it cannot allocate memory for the extra space. 3352 This function never shrinks the stack; 3353 if the stack already has space for the extra slots, 3354 it is left unchanged. 3355 3356 3357 3358 3359 3360 <hr><h3><a name="lua_close"><code>lua_close</code></a></h3><p> 3361 <span class="apii">[-0, +0, –]</span> 3362 <pre>void lua_close (lua_State *L);</pre> 3363 3364 <p> 3365 Destroys all objects in the given Lua state 3366 (calling the corresponding garbage-collection metamethods, if any) 3367 and frees all dynamic memory used by this state. 3368 In several platforms, you may not need to call this function, 3369 because all resources are naturally released when the host program ends. 3370 On the other hand, long-running programs that create multiple states, 3371 such as daemons or web servers, 3372 will probably need to close states as soon as they are not needed. 3373 3374 3375 3376 3377 3378 <hr><h3><a name="lua_compare"><code>lua_compare</code></a></h3><p> 3379 <span class="apii">[-0, +0, <em>e</em>]</span> 3380 <pre>int lua_compare (lua_State *L, int index1, int index2, int op);</pre> 3381 3382 <p> 3383 Compares two Lua values. 3384 Returns 1 if the value at index <code>index1</code> satisfies <code>op</code> 3385 when compared with the value at index <code>index2</code>, 3386 following the semantics of the corresponding Lua operator 3387 (that is, it may call metamethods). 3388 Otherwise returns 0. 3389 Also returns 0 if any of the indices is not valid. 3390 3391 3392 <p> 3393 The value of <code>op</code> must be one of the following constants: 3394 3395 <ul> 3396 3397 <li><b><a name="pdf-LUA_OPEQ"><code>LUA_OPEQ</code></a>: </b> compares for equality (<code>==</code>)</li> 3398 <li><b><a name="pdf-LUA_OPLT"><code>LUA_OPLT</code></a>: </b> compares for less than (<code><</code>)</li> 3399 <li><b><a name="pdf-LUA_OPLE"><code>LUA_OPLE</code></a>: </b> compares for less or equal (<code><=</code>)</li> 3400 3401 </ul> 3402 3403 3404 3405 3406 <hr><h3><a name="lua_concat"><code>lua_concat</code></a></h3><p> 3407 <span class="apii">[-n, +1, <em>e</em>]</span> 3408 <pre>void lua_concat (lua_State *L, int n);</pre> 3409 3410 <p> 3411 Concatenates the <code>n</code> values at the top of the stack, 3412 pops them, and leaves the result at the top. 3413 If <code>n</code> is 1, the result is the single value on the stack 3414 (that is, the function does nothing); 3415 if <code>n</code> is 0, the result is the empty string. 3416 Concatenation is performed following the usual semantics of Lua 3417 (see <a href="#3.4.6">§3.4.6</a>). 3418 3419 3420 3421 3422 3423 <hr><h3><a name="lua_copy"><code>lua_copy</code></a></h3><p> 3424 <span class="apii">[-0, +0, –]</span> 3425 <pre>void lua_copy (lua_State *L, int fromidx, int toidx);</pre> 3426 3427 <p> 3428 Copies the element at index <code>fromidx</code> 3429 into the valid index <code>toidx</code>, 3430 replacing the value at that position. 3431 Values at other positions are not affected. 3432 3433 3434 3435 3436 3437 <hr><h3><a name="lua_createtable"><code>lua_createtable</code></a></h3><p> 3438 <span class="apii">[-0, +1, <em>m</em>]</span> 3439 <pre>void lua_createtable (lua_State *L, int narr, int nrec);</pre> 3440 3441 <p> 3442 Creates a new empty table and pushes it onto the stack. 3443 Parameter <code>narr</code> is a hint for how many elements the table 3444 will have as a sequence; 3445 parameter <code>nrec</code> is a hint for how many other elements 3446 the table will have. 3447 Lua may use these hints to preallocate memory for the new table. 3448 This preallocation is useful for performance when you know in advance 3449 how many elements the table will have. 3450 Otherwise you can use the function <a href="#lua_newtable"><code>lua_newtable</code></a>. 3451 3452 3453 3454 3455 3456 <hr><h3><a name="lua_dump"><code>lua_dump</code></a></h3><p> 3457 <span class="apii">[-0, +0, –]</span> 3458 <pre>int lua_dump (lua_State *L, 3459 lua_Writer writer, 3460 void *data, 3461 int strip);</pre> 3462 3463 <p> 3464 Dumps a function as a binary chunk. 3465 Receives a Lua function on the top of the stack 3466 and produces a binary chunk that, 3467 if loaded again, 3468 results in a function equivalent to the one dumped. 3469 As it produces parts of the chunk, 3470 <a href="#lua_dump"><code>lua_dump</code></a> calls function <code>writer</code> (see <a href="#lua_Writer"><code>lua_Writer</code></a>) 3471 with the given <code>data</code> 3472 to write them. 3473 3474 3475 <p> 3476 If <code>strip</code> is true, 3477 the binary representation may not include all debug information 3478 about the function, 3479 to save space. 3480 3481 3482 <p> 3483 The value returned is the error code returned by the last 3484 call to the writer; 3485 0 means no errors. 3486 3487 3488 <p> 3489 This function does not pop the Lua function from the stack. 3490 3491 3492 3493 3494 3495 <hr><h3><a name="lua_error"><code>lua_error</code></a></h3><p> 3496 <span class="apii">[-1, +0, <em>v</em>]</span> 3497 <pre>int lua_error (lua_State *L);</pre> 3498 3499 <p> 3500 Generates a Lua error, 3501 using the value at the top of the stack as the error object. 3502 This function does a long jump, 3503 and therefore never returns 3504 (see <a href="#luaL_error"><code>luaL_error</code></a>). 3505 3506 3507 3508 3509 3510 <hr><h3><a name="lua_gc"><code>lua_gc</code></a></h3><p> 3511 <span class="apii">[-0, +0, <em>m</em>]</span> 3512 <pre>int lua_gc (lua_State *L, int what, int data);</pre> 3513 3514 <p> 3515 Controls the garbage collector. 3516 3517 3518 <p> 3519 This function performs several tasks, 3520 according to the value of the parameter <code>what</code>: 3521 3522 <ul> 3523 3524 <li><b><code>LUA_GCSTOP</code>: </b> 3525 stops the garbage collector. 3526 </li> 3527 3528 <li><b><code>LUA_GCRESTART</code>: </b> 3529 restarts the garbage collector. 3530 </li> 3531 3532 <li><b><code>LUA_GCCOLLECT</code>: </b> 3533 performs a full garbage-collection cycle. 3534 </li> 3535 3536 <li><b><code>LUA_GCCOUNT</code>: </b> 3537 returns the current amount of memory (in Kbytes) in use by Lua. 3538 </li> 3539 3540 <li><b><code>LUA_GCCOUNTB</code>: </b> 3541 returns the remainder of dividing the current amount of bytes of 3542 memory in use by Lua by 1024. 3543 </li> 3544 3545 <li><b><code>LUA_GCSTEP</code>: </b> 3546 performs an incremental step of garbage collection. 3547 </li> 3548 3549 <li><b><code>LUA_GCSETPAUSE</code>: </b> 3550 sets <code>data</code> as the new value 3551 for the <em>pause</em> of the collector (see <a href="#2.5">§2.5</a>) 3552 and returns the previous value of the pause. 3553 </li> 3554 3555 <li><b><code>LUA_GCSETSTEPMUL</code>: </b> 3556 sets <code>data</code> as the new value for the <em>step multiplier</em> of 3557 the collector (see <a href="#2.5">§2.5</a>) 3558 and returns the previous value of the step multiplier. 3559 </li> 3560 3561 <li><b><code>LUA_GCISRUNNING</code>: </b> 3562 returns a boolean that tells whether the collector is running 3563 (i.e., not stopped). 3564 </li> 3565 3566 </ul> 3567 3568 <p> 3569 For more details about these options, 3570 see <a href="#pdf-collectgarbage"><code>collectgarbage</code></a>. 3571 3572 3573 3574 3575 3576 <hr><h3><a name="lua_getallocf"><code>lua_getallocf</code></a></h3><p> 3577 <span class="apii">[-0, +0, –]</span> 3578 <pre>lua_Alloc lua_getallocf (lua_State *L, void **ud);</pre> 3579 3580 <p> 3581 Returns the memory-allocation function of a given state. 3582 If <code>ud</code> is not <code>NULL</code>, Lua stores in <code>*ud</code> the 3583 opaque pointer given when the memory-allocator function was set. 3584 3585 3586 3587 3588 3589 <hr><h3><a name="lua_getfield"><code>lua_getfield</code></a></h3><p> 3590 <span class="apii">[-0, +1, <em>e</em>]</span> 3591 <pre>int lua_getfield (lua_State *L, int index, const char *k);</pre> 3592 3593 <p> 3594 Pushes onto the stack the value <code>t[k]</code>, 3595 where <code>t</code> is the value at the given index. 3596 As in Lua, this function may trigger a metamethod 3597 for the "index" event (see <a href="#2.4">§2.4</a>). 3598 3599 3600 <p> 3601 Returns the type of the pushed value. 3602 3603 3604 3605 3606 3607 <hr><h3><a name="lua_getextraspace"><code>lua_getextraspace</code></a></h3><p> 3608 <span class="apii">[-0, +0, –]</span> 3609 <pre>void *lua_getextraspace (lua_State *L);</pre> 3610 3611 <p> 3612 Returns a pointer to a raw memory area associated with the 3613 given Lua state. 3614 The application can use this area for any purpose; 3615 Lua does not use it for anything. 3616 3617 3618 <p> 3619 Each new thread has this area initialized with a copy 3620 of the area of the main thread. 3621 3622 3623 <p> 3624 By default, this area has the size of a pointer to void, 3625 but you can recompile Lua with a different size for this area. 3626 (See <code>LUA_EXTRASPACE</code> in <code>luaconf.h</code>.) 3627 3628 3629 3630 3631 3632 <hr><h3><a name="lua_getglobal"><code>lua_getglobal</code></a></h3><p> 3633 <span class="apii">[-0, +1, <em>e</em>]</span> 3634 <pre>int lua_getglobal (lua_State *L, const char *name);</pre> 3635 3636 <p> 3637 Pushes onto the stack the value of the global <code>name</code>. 3638 Returns the type of that value. 3639 3640 3641 3642 3643 3644 <hr><h3><a name="lua_geti"><code>lua_geti</code></a></h3><p> 3645 <span class="apii">[-0, +1, <em>e</em>]</span> 3646 <pre>int lua_geti (lua_State *L, int index, lua_Integer i);</pre> 3647 3648 <p> 3649 Pushes onto the stack the value <code>t[i]</code>, 3650 where <code>t</code> is the value at the given index. 3651 As in Lua, this function may trigger a metamethod 3652 for the "index" event (see <a href="#2.4">§2.4</a>). 3653 3654 3655 <p> 3656 Returns the type of the pushed value. 3657 3658 3659 3660 3661 3662 <hr><h3><a name="lua_getmetatable"><code>lua_getmetatable</code></a></h3><p> 3663 <span class="apii">[-0, +(0|1), –]</span> 3664 <pre>int lua_getmetatable (lua_State *L, int index);</pre> 3665 3666 <p> 3667 If the value at the given index has a metatable, 3668 the function pushes that metatable onto the stack and returns 1. 3669 Otherwise, 3670 the function returns 0 and pushes nothing on the stack. 3671 3672 3673 3674 3675 3676 <hr><h3><a name="lua_gettable"><code>lua_gettable</code></a></h3><p> 3677 <span class="apii">[-1, +1, <em>e</em>]</span> 3678 <pre>int lua_gettable (lua_State *L, int index);</pre> 3679 3680 <p> 3681 Pushes onto the stack the value <code>t[k]</code>, 3682 where <code>t</code> is the value at the given index 3683 and <code>k</code> is the value at the top of the stack. 3684 3685 3686 <p> 3687 This function pops the key from the stack, 3688 pushing the resulting value in its place. 3689 As in Lua, this function may trigger a metamethod 3690 for the "index" event (see <a href="#2.4">§2.4</a>). 3691 3692 3693 <p> 3694 Returns the type of the pushed value. 3695 3696 3697 3698 3699 3700 <hr><h3><a name="lua_gettop"><code>lua_gettop</code></a></h3><p> 3701 <span class="apii">[-0, +0, –]</span> 3702 <pre>int lua_gettop (lua_State *L);</pre> 3703 3704 <p> 3705 Returns the index of the top element in the stack. 3706 Because indices start at 1, 3707 this result is equal to the number of elements in the stack; 3708 in particular, 0 means an empty stack. 3709 3710 3711 3712 3713 3714 <hr><h3><a name="lua_getuservalue"><code>lua_getuservalue</code></a></h3><p> 3715 <span class="apii">[-0, +1, –]</span> 3716 <pre>int lua_getuservalue (lua_State *L, int index);</pre> 3717 3718 <p> 3719 Pushes onto the stack the Lua value associated with the full userdata 3720 at the given index. 3721 3722 3723 <p> 3724 Returns the type of the pushed value. 3725 3726 3727 3728 3729 3730 <hr><h3><a name="lua_insert"><code>lua_insert</code></a></h3><p> 3731 <span class="apii">[-1, +1, –]</span> 3732 <pre>void lua_insert (lua_State *L, int index);</pre> 3733 3734 <p> 3735 Moves the top element into the given valid index, 3736 shifting up the elements above this index to open space. 3737 This function cannot be called with a pseudo-index, 3738 because a pseudo-index is not an actual stack position. 3739 3740 3741 3742 3743 3744 <hr><h3><a name="lua_Integer"><code>lua_Integer</code></a></h3> 3745 <pre>typedef ... lua_Integer;</pre> 3746 3747 <p> 3748 The type of integers in Lua. 3749 3750 3751 <p> 3752 By default this type is <code>long long</code>, 3753 (usually a 64-bit two-complement integer), 3754 but that can be changed to <code>long</code> or <code>int</code> 3755 (usually a 32-bit two-complement integer). 3756 (See <code>LUA_INT_TYPE</code> in <code>luaconf.h</code>.) 3757 3758 3759 <p> 3760 Lua also defines the constants 3761 <a name="pdf-LUA_MININTEGER"><code>LUA_MININTEGER</code></a> and <a name="pdf-LUA_MAXINTEGER"><code>LUA_MAXINTEGER</code></a>, 3762 with the minimum and the maximum values that fit in this type. 3763 3764 3765 3766 3767 3768 <hr><h3><a name="lua_isboolean"><code>lua_isboolean</code></a></h3><p> 3769 <span class="apii">[-0, +0, –]</span> 3770 <pre>int lua_isboolean (lua_State *L, int index);</pre> 3771 3772 <p> 3773 Returns 1 if the value at the given index is a boolean, 3774 and 0 otherwise. 3775 3776 3777 3778 3779 3780 <hr><h3><a name="lua_iscfunction"><code>lua_iscfunction</code></a></h3><p> 3781 <span class="apii">[-0, +0, –]</span> 3782 <pre>int lua_iscfunction (lua_State *L, int index);</pre> 3783 3784 <p> 3785 Returns 1 if the value at the given index is a C function, 3786 and 0 otherwise. 3787 3788 3789 3790 3791 3792 <hr><h3><a name="lua_isfunction"><code>lua_isfunction</code></a></h3><p> 3793 <span class="apii">[-0, +0, –]</span> 3794 <pre>int lua_isfunction (lua_State *L, int index);</pre> 3795 3796 <p> 3797 Returns 1 if the value at the given index is a function 3798 (either C or Lua), and 0 otherwise. 3799 3800 3801 3802 3803 3804 <hr><h3><a name="lua_isinteger"><code>lua_isinteger</code></a></h3><p> 3805 <span class="apii">[-0, +0, –]</span> 3806 <pre>int lua_isinteger (lua_State *L, int index);</pre> 3807 3808 <p> 3809 Returns 1 if the value at the given index is an integer 3810 (that is, the value is a number and is represented as an integer), 3811 and 0 otherwise. 3812 3813 3814 3815 3816 3817 <hr><h3><a name="lua_islightuserdata"><code>lua_islightuserdata</code></a></h3><p> 3818 <span class="apii">[-0, +0, –]</span> 3819 <pre>int lua_islightuserdata (lua_State *L, int index);</pre> 3820 3821 <p> 3822 Returns 1 if the value at the given index is a light userdata, 3823 and 0 otherwise. 3824 3825 3826 3827 3828 3829 <hr><h3><a name="lua_isnil"><code>lua_isnil</code></a></h3><p> 3830 <span class="apii">[-0, +0, –]</span> 3831 <pre>int lua_isnil (lua_State *L, int index);</pre> 3832 3833 <p> 3834 Returns 1 if the value at the given index is <b>nil</b>, 3835 and 0 otherwise. 3836 3837 3838 3839 3840 3841 <hr><h3><a name="lua_isnone"><code>lua_isnone</code></a></h3><p> 3842 <span class="apii">[-0, +0, –]</span> 3843 <pre>int lua_isnone (lua_State *L, int index);</pre> 3844 3845 <p> 3846 Returns 1 if the given index is not valid, 3847 and 0 otherwise. 3848 3849 3850 3851 3852 3853 <hr><h3><a name="lua_isnoneornil"><code>lua_isnoneornil</code></a></h3><p> 3854 <span class="apii">[-0, +0, –]</span> 3855 <pre>int lua_isnoneornil (lua_State *L, int index);</pre> 3856 3857 <p> 3858 Returns 1 if the given index is not valid 3859 or if the value at this index is <b>nil</b>, 3860 and 0 otherwise. 3861 3862 3863 3864 3865 3866 <hr><h3><a name="lua_isnumber"><code>lua_isnumber</code></a></h3><p> 3867 <span class="apii">[-0, +0, –]</span> 3868 <pre>int lua_isnumber (lua_State *L, int index);</pre> 3869 3870 <p> 3871 Returns 1 if the value at the given index is a number 3872 or a string convertible to a number, 3873 and 0 otherwise. 3874 3875 3876 3877 3878 3879 <hr><h3><a name="lua_isstring"><code>lua_isstring</code></a></h3><p> 3880 <span class="apii">[-0, +0, –]</span> 3881 <pre>int lua_isstring (lua_State *L, int index);</pre> 3882 3883 <p> 3884 Returns 1 if the value at the given index is a string 3885 or a number (which is always convertible to a string), 3886 and 0 otherwise. 3887 3888 3889 3890 3891 3892 <hr><h3><a name="lua_istable"><code>lua_istable</code></a></h3><p> 3893 <span class="apii">[-0, +0, –]</span> 3894 <pre>int lua_istable (lua_State *L, int index);</pre> 3895 3896 <p> 3897 Returns 1 if the value at the given index is a table, 3898 and 0 otherwise. 3899 3900 3901 3902 3903 3904 <hr><h3><a name="lua_isthread"><code>lua_isthread</code></a></h3><p> 3905 <span class="apii">[-0, +0, –]</span> 3906 <pre>int lua_isthread (lua_State *L, int index);</pre> 3907 3908 <p> 3909 Returns 1 if the value at the given index is a thread, 3910 and 0 otherwise. 3911 3912 3913 3914 3915 3916 <hr><h3><a name="lua_isuserdata"><code>lua_isuserdata</code></a></h3><p> 3917 <span class="apii">[-0, +0, –]</span> 3918 <pre>int lua_isuserdata (lua_State *L, int index);</pre> 3919 3920 <p> 3921 Returns 1 if the value at the given index is a userdata 3922 (either full or light), and 0 otherwise. 3923 3924 3925 3926 3927 3928 <hr><h3><a name="lua_isyieldable"><code>lua_isyieldable</code></a></h3><p> 3929 <span class="apii">[-0, +0, –]</span> 3930 <pre>int lua_isyieldable (lua_State *L);</pre> 3931 3932 <p> 3933 Returns 1 if the given coroutine can yield, 3934 and 0 otherwise. 3935 3936 3937 3938 3939 3940 <hr><h3><a name="lua_KContext"><code>lua_KContext</code></a></h3> 3941 <pre>typedef ... lua_KContext;</pre> 3942 3943 <p> 3944 The type for continuation-function contexts. 3945 It must be a numeric type. 3946 This type is defined as <code>intptr_t</code> 3947 when <code>intptr_t</code> is available, 3948 so that it can store pointers too. 3949 Otherwise, it is defined as <code>ptrdiff_t</code>. 3950 3951 3952 3953 3954 3955 <hr><h3><a name="lua_KFunction"><code>lua_KFunction</code></a></h3> 3956 <pre>typedef int (*lua_KFunction) (lua_State *L, int status, lua_KContext ctx);</pre> 3957 3958 <p> 3959 Type for continuation functions (see <a href="#4.7">§4.7</a>). 3960 3961 3962 3963 3964 3965 <hr><h3><a name="lua_len"><code>lua_len</code></a></h3><p> 3966 <span class="apii">[-0, +1, <em>e</em>]</span> 3967 <pre>void lua_len (lua_State *L, int index);</pre> 3968 3969 <p> 3970 Returns the length of the value at the given index. 3971 It is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>) and 3972 may trigger a metamethod for the "length" event (see <a href="#2.4">§2.4</a>). 3973 The result is pushed on the stack. 3974 3975 3976 3977 3978 3979 <hr><h3><a name="lua_load"><code>lua_load</code></a></h3><p> 3980 <span class="apii">[-0, +1, –]</span> 3981 <pre>int lua_load (lua_State *L, 3982 lua_Reader reader, 3983 void *data, 3984 const char *chunkname, 3985 const char *mode);</pre> 3986 3987 <p> 3988 Loads a Lua chunk without running it. 3989 If there are no errors, 3990 <code>lua_load</code> pushes the compiled chunk as a Lua 3991 function on top of the stack. 3992 Otherwise, it pushes an error message. 3993 3994 3995 <p> 3996 The return values of <code>lua_load</code> are: 3997 3998 <ul> 3999 4000 <li><b><a href="#pdf-LUA_OK"><code>LUA_OK</code></a>: </b> no errors;</li> 4001 4002 <li><b><a name="pdf-LUA_ERRSYNTAX"><code>LUA_ERRSYNTAX</code></a>: </b> 4003 syntax error during precompilation;</li> 4004 4005 <li><b><a href="#pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b> 4006 memory allocation (out-of-memory) error;</li> 4007 4008 <li><b><a href="#pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b> 4009 error while running a <code>__gc</code> metamethod. 4010 (This error has no relation with the chunk being loaded. 4011 It is generated by the garbage collector.) 4012 </li> 4013 4014 </ul> 4015 4016 <p> 4017 The <code>lua_load</code> function uses a user-supplied <code>reader</code> function 4018 to read the chunk (see <a href="#lua_Reader"><code>lua_Reader</code></a>). 4019 The <code>data</code> argument is an opaque value passed to the reader function. 4020 4021 4022 <p> 4023 The <code>chunkname</code> argument gives a name to the chunk, 4024 which is used for error messages and in debug information (see <a href="#4.9">§4.9</a>). 4025 4026 4027 <p> 4028 <code>lua_load</code> automatically detects whether the chunk is text or binary 4029 and loads it accordingly (see program <code>luac</code>). 4030 The string <code>mode</code> works as in function <a href="#pdf-load"><code>load</code></a>, 4031 with the addition that 4032 a <code>NULL</code> value is equivalent to the string "<code>bt</code>". 4033 4034 4035 <p> 4036 <code>lua_load</code> uses the stack internally, 4037 so the reader function must always leave the stack 4038 unmodified when returning. 4039 4040 4041 <p> 4042 If the resulting function has upvalues, 4043 its first upvalue is set to the value of the global environment 4044 stored at index <code>LUA_RIDX_GLOBALS</code> in the registry (see <a href="#4.5">§4.5</a>). 4045 When loading main chunks, 4046 this upvalue will be the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>). 4047 Other upvalues are initialized with <b>nil</b>. 4048 4049 4050 4051 4052 4053 <hr><h3><a name="lua_newstate"><code>lua_newstate</code></a></h3><p> 4054 <span class="apii">[-0, +0, –]</span> 4055 <pre>lua_State *lua_newstate (lua_Alloc f, void *ud);</pre> 4056 4057 <p> 4058 Creates a new thread running in a new, independent state. 4059 Returns <code>NULL</code> if it cannot create the thread or the state 4060 (due to lack of memory). 4061 The argument <code>f</code> is the allocator function; 4062 Lua does all memory allocation for this state 4063 through this function (see <a href="#lua_Alloc"><code>lua_Alloc</code></a>). 4064 The second argument, <code>ud</code>, is an opaque pointer that Lua 4065 passes to the allocator in every call. 4066 4067 4068 4069 4070 4071 <hr><h3><a name="lua_newtable"><code>lua_newtable</code></a></h3><p> 4072 <span class="apii">[-0, +1, <em>m</em>]</span> 4073 <pre>void lua_newtable (lua_State *L);</pre> 4074 4075 <p> 4076 Creates a new empty table and pushes it onto the stack. 4077 It is equivalent to <code>lua_createtable(L, 0, 0)</code>. 4078 4079 4080 4081 4082 4083 <hr><h3><a name="lua_newthread"><code>lua_newthread</code></a></h3><p> 4084 <span class="apii">[-0, +1, <em>m</em>]</span> 4085 <pre>lua_State *lua_newthread (lua_State *L);</pre> 4086 4087 <p> 4088 Creates a new thread, pushes it on the stack, 4089 and returns a pointer to a <a href="#lua_State"><code>lua_State</code></a> that represents this new thread. 4090 The new thread returned by this function shares with the original thread 4091 its global environment, 4092 but has an independent execution stack. 4093 4094 4095 <p> 4096 There is no explicit function to close or to destroy a thread. 4097 Threads are subject to garbage collection, 4098 like any Lua object. 4099 4100 4101 4102 4103 4104 <hr><h3><a name="lua_newuserdata"><code>lua_newuserdata</code></a></h3><p> 4105 <span class="apii">[-0, +1, <em>m</em>]</span> 4106 <pre>void *lua_newuserdata (lua_State *L, size_t size);</pre> 4107 4108 <p> 4109 This function allocates a new block of memory with the given size, 4110 pushes onto the stack a new full userdata with the block address, 4111 and returns this address. 4112 The host program can freely use this memory. 4113 4114 4115 4116 4117 4118 <hr><h3><a name="lua_next"><code>lua_next</code></a></h3><p> 4119 <span class="apii">[-1, +(2|0), <em>e</em>]</span> 4120 <pre>int lua_next (lua_State *L, int index);</pre> 4121 4122 <p> 4123 Pops a key from the stack, 4124 and pushes a key–value pair from the table at the given index 4125 (the "next" pair after the given key). 4126 If there are no more elements in the table, 4127 then <a href="#lua_next"><code>lua_next</code></a> returns 0 (and pushes nothing). 4128 4129 4130 <p> 4131 A typical traversal looks like this: 4132 4133 <pre> 4134 /* table is in the stack at index 't' */ 4135 lua_pushnil(L); /* first key */ 4136 while (lua_next(L, t) != 0) { 4137 /* uses 'key' (at index -2) and 'value' (at index -1) */ 4138 printf("%s - %s\n", 4139 lua_typename(L, lua_type(L, -2)), 4140 lua_typename(L, lua_type(L, -1))); 4141 /* removes 'value'; keeps 'key' for next iteration */ 4142 lua_pop(L, 1); 4143 } 4144 </pre> 4145 4146 <p> 4147 While traversing a table, 4148 do not call <a href="#lua_tolstring"><code>lua_tolstring</code></a> directly on a key, 4149 unless you know that the key is actually a string. 4150 Recall that <a href="#lua_tolstring"><code>lua_tolstring</code></a> may change 4151 the value at the given index; 4152 this confuses the next call to <a href="#lua_next"><code>lua_next</code></a>. 4153 4154 4155 <p> 4156 See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying 4157 the table during its traversal. 4158 4159 4160 4161 4162 4163 <hr><h3><a name="lua_Number"><code>lua_Number</code></a></h3> 4164 <pre>typedef ... lua_Number;</pre> 4165 4166 <p> 4167 The type of floats in Lua. 4168 4169 4170 <p> 4171 By default this type is double, 4172 but that can be changed to a single float or a long double. 4173 (See <code>LUA_FLOAT_TYPE</code> in <code>luaconf.h</code>.) 4174 4175 4176 4177 4178 4179 <hr><h3><a name="lua_numbertointeger"><code>lua_numbertointeger</code></a></h3> 4180 <pre>int lua_numbertointeger (lua_Number n, lua_Integer *p);</pre> 4181 4182 <p> 4183 Converts a Lua float to a Lua integer. 4184 This macro assumes that <code>n</code> has an integral value. 4185 If that value is within the range of Lua integers, 4186 it is converted to an integer and assigned to <code>*p</code>. 4187 The macro results in a boolean indicating whether the 4188 conversion was successful. 4189 (Note that this range test can be tricky to do 4190 correctly without this macro, 4191 due to roundings.) 4192 4193 4194 <p> 4195 This macro may evaluate its arguments more than once. 4196 4197 4198 4199 4200 4201 <hr><h3><a name="lua_pcall"><code>lua_pcall</code></a></h3><p> 4202 <span class="apii">[-(nargs + 1), +(nresults|1), –]</span> 4203 <pre>int lua_pcall (lua_State *L, int nargs, int nresults, int msgh);</pre> 4204 4205 <p> 4206 Calls a function in protected mode. 4207 4208 4209 <p> 4210 Both <code>nargs</code> and <code>nresults</code> have the same meaning as 4211 in <a href="#lua_call"><code>lua_call</code></a>. 4212 If there are no errors during the call, 4213 <a href="#lua_pcall"><code>lua_pcall</code></a> behaves exactly like <a href="#lua_call"><code>lua_call</code></a>. 4214 However, if there is any error, 4215 <a href="#lua_pcall"><code>lua_pcall</code></a> catches it, 4216 pushes a single value on the stack (the error object), 4217 and returns an error code. 4218 Like <a href="#lua_call"><code>lua_call</code></a>, 4219 <a href="#lua_pcall"><code>lua_pcall</code></a> always removes the function 4220 and its arguments from the stack. 4221 4222 4223 <p> 4224 If <code>msgh</code> is 0, 4225 then the error object returned on the stack 4226 is exactly the original error object. 4227 Otherwise, <code>msgh</code> is the stack index of a 4228 <em>message handler</em>. 4229 (This index cannot be a pseudo-index.) 4230 In case of runtime errors, 4231 this function will be called with the error object 4232 and its return value will be the object 4233 returned on the stack by <a href="#lua_pcall"><code>lua_pcall</code></a>. 4234 4235 4236 <p> 4237 Typically, the message handler is used to add more debug 4238 information to the error object, such as a stack traceback. 4239 Such information cannot be gathered after the return of <a href="#lua_pcall"><code>lua_pcall</code></a>, 4240 since by then the stack has unwound. 4241 4242 4243 <p> 4244 The <a href="#lua_pcall"><code>lua_pcall</code></a> function returns one of the following constants 4245 (defined in <code>lua.h</code>): 4246 4247 <ul> 4248 4249 <li><b><a name="pdf-LUA_OK"><code>LUA_OK</code></a> (0): </b> 4250 success.</li> 4251 4252 <li><b><a name="pdf-LUA_ERRRUN"><code>LUA_ERRRUN</code></a>: </b> 4253 a runtime error. 4254 </li> 4255 4256 <li><b><a name="pdf-LUA_ERRMEM"><code>LUA_ERRMEM</code></a>: </b> 4257 memory allocation error. 4258 For such errors, Lua does not call the message handler. 4259 </li> 4260 4261 <li><b><a name="pdf-LUA_ERRERR"><code>LUA_ERRERR</code></a>: </b> 4262 error while running the message handler. 4263 </li> 4264 4265 <li><b><a name="pdf-LUA_ERRGCMM"><code>LUA_ERRGCMM</code></a>: </b> 4266 error while running a <code>__gc</code> metamethod. 4267 For such errors, Lua does not call the message handler 4268 (as this kind of error typically has no relation 4269 with the function being called). 4270 </li> 4271 4272 </ul> 4273 4274 4275 4276 4277 <hr><h3><a name="lua_pcallk"><code>lua_pcallk</code></a></h3><p> 4278 <span class="apii">[-(nargs + 1), +(nresults|1), –]</span> 4279 <pre>int lua_pcallk (lua_State *L, 4280 int nargs, 4281 int nresults, 4282 int msgh, 4283 lua_KContext ctx, 4284 lua_KFunction k);</pre> 4285 4286 <p> 4287 This function behaves exactly like <a href="#lua_pcall"><code>lua_pcall</code></a>, 4288 but allows the called function to yield (see <a href="#4.7">§4.7</a>). 4289 4290 4291 4292 4293 4294 <hr><h3><a name="lua_pop"><code>lua_pop</code></a></h3><p> 4295 <span class="apii">[-n, +0, –]</span> 4296 <pre>void lua_pop (lua_State *L, int n);</pre> 4297 4298 <p> 4299 Pops <code>n</code> elements from the stack. 4300 4301 4302 4303 4304 4305 <hr><h3><a name="lua_pushboolean"><code>lua_pushboolean</code></a></h3><p> 4306 <span class="apii">[-0, +1, –]</span> 4307 <pre>void lua_pushboolean (lua_State *L, int b);</pre> 4308 4309 <p> 4310 Pushes a boolean value with value <code>b</code> onto the stack. 4311 4312 4313 4314 4315 4316 <hr><h3><a name="lua_pushcclosure"><code>lua_pushcclosure</code></a></h3><p> 4317 <span class="apii">[-n, +1, <em>m</em>]</span> 4318 <pre>void lua_pushcclosure (lua_State *L, lua_CFunction fn, int n);</pre> 4319 4320 <p> 4321 Pushes a new C closure onto the stack. 4322 4323 4324 <p> 4325 When a C function is created, 4326 it is possible to associate some values with it, 4327 thus creating a C closure (see <a href="#4.4">§4.4</a>); 4328 these values are then accessible to the function whenever it is called. 4329 To associate values with a C function, 4330 first these values must be pushed onto the stack 4331 (when there are multiple values, the first value is pushed first). 4332 Then <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> 4333 is called to create and push the C function onto the stack, 4334 with the argument <code>n</code> telling how many values will be 4335 associated with the function. 4336 <a href="#lua_pushcclosure"><code>lua_pushcclosure</code></a> also pops these values from the stack. 4337 4338 4339 <p> 4340 The maximum value for <code>n</code> is 255. 4341 4342 4343 <p> 4344 When <code>n</code> is zero, 4345 this function creates a <em>light C function</em>, 4346 which is just a pointer to the C function. 4347 In that case, it never raises a memory error. 4348 4349 4350 4351 4352 4353 <hr><h3><a name="lua_pushcfunction"><code>lua_pushcfunction</code></a></h3><p> 4354 <span class="apii">[-0, +1, –]</span> 4355 <pre>void lua_pushcfunction (lua_State *L, lua_CFunction f);</pre> 4356 4357 <p> 4358 Pushes a C function onto the stack. 4359 This function receives a pointer to a C function 4360 and pushes onto the stack a Lua value of type <code>function</code> that, 4361 when called, invokes the corresponding C function. 4362 4363 4364 <p> 4365 Any function to be callable by Lua must 4366 follow the correct protocol to receive its parameters 4367 and return its results (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). 4368 4369 4370 4371 4372 4373 <hr><h3><a name="lua_pushfstring"><code>lua_pushfstring</code></a></h3><p> 4374 <span class="apii">[-0, +1, <em>e</em>]</span> 4375 <pre>const char *lua_pushfstring (lua_State *L, const char *fmt, ...);</pre> 4376 4377 <p> 4378 Pushes onto the stack a formatted string 4379 and returns a pointer to this string. 4380 It is similar to the ISO C function <code>sprintf</code>, 4381 but has some important differences: 4382 4383 <ul> 4384 4385 <li> 4386 You do not have to allocate space for the result: 4387 the result is a Lua string and Lua takes care of memory allocation 4388 (and deallocation, through garbage collection). 4389 </li> 4390 4391 <li> 4392 The conversion specifiers are quite restricted. 4393 There are no flags, widths, or precisions. 4394 The conversion specifiers can only be 4395 '<code>%%</code>' (inserts the character '<code>%</code>'), 4396 '<code>%s</code>' (inserts a zero-terminated string, with no size restrictions), 4397 '<code>%f</code>' (inserts a <a href="#lua_Number"><code>lua_Number</code></a>), 4398 '<code>%I</code>' (inserts a <a href="#lua_Integer"><code>lua_Integer</code></a>), 4399 '<code>%p</code>' (inserts a pointer as a hexadecimal numeral), 4400 '<code>%d</code>' (inserts an <code>int</code>), 4401 '<code>%c</code>' (inserts an <code>int</code> as a one-byte character), and 4402 '<code>%U</code>' (inserts a <code>long int</code> as a UTF-8 byte sequence). 4403 </li> 4404 4405 </ul> 4406 4407 <p> 4408 Unlike other push functions, 4409 this function checks for the stack space it needs, 4410 including the slot for its result. 4411 4412 4413 4414 4415 4416 <hr><h3><a name="lua_pushglobaltable"><code>lua_pushglobaltable</code></a></h3><p> 4417 <span class="apii">[-0, +1, –]</span> 4418 <pre>void lua_pushglobaltable (lua_State *L);</pre> 4419 4420 <p> 4421 Pushes the global environment onto the stack. 4422 4423 4424 4425 4426 4427 <hr><h3><a name="lua_pushinteger"><code>lua_pushinteger</code></a></h3><p> 4428 <span class="apii">[-0, +1, –]</span> 4429 <pre>void lua_pushinteger (lua_State *L, lua_Integer n);</pre> 4430 4431 <p> 4432 Pushes an integer with value <code>n</code> onto the stack. 4433 4434 4435 4436 4437 4438 <hr><h3><a name="lua_pushlightuserdata"><code>lua_pushlightuserdata</code></a></h3><p> 4439 <span class="apii">[-0, +1, –]</span> 4440 <pre>void lua_pushlightuserdata (lua_State *L, void *p);</pre> 4441 4442 <p> 4443 Pushes a light userdata onto the stack. 4444 4445 4446 <p> 4447 Userdata represent C values in Lua. 4448 A <em>light userdata</em> represents a pointer, a <code>void*</code>. 4449 It is a value (like a number): 4450 you do not create it, it has no individual metatable, 4451 and it is not collected (as it was never created). 4452 A light userdata is equal to "any" 4453 light userdata with the same C address. 4454 4455 4456 4457 4458 4459 <hr><h3><a name="lua_pushliteral"><code>lua_pushliteral</code></a></h3><p> 4460 <span class="apii">[-0, +1, <em>m</em>]</span> 4461 <pre>const char *lua_pushliteral (lua_State *L, const char *s);</pre> 4462 4463 <p> 4464 This macro is equivalent to <a href="#lua_pushstring"><code>lua_pushstring</code></a>, 4465 but should be used only when <code>s</code> is a literal string. 4466 4467 4468 4469 4470 4471 <hr><h3><a name="lua_pushlstring"><code>lua_pushlstring</code></a></h3><p> 4472 <span class="apii">[-0, +1, <em>m</em>]</span> 4473 <pre>const char *lua_pushlstring (lua_State *L, const char *s, size_t len);</pre> 4474 4475 <p> 4476 Pushes the string pointed to by <code>s</code> with size <code>len</code> 4477 onto the stack. 4478 Lua makes (or reuses) an internal copy of the given string, 4479 so the memory at <code>s</code> can be freed or reused immediately after 4480 the function returns. 4481 The string can contain any binary data, 4482 including embedded zeros. 4483 4484 4485 <p> 4486 Returns a pointer to the internal copy of the string. 4487 4488 4489 4490 4491 4492 <hr><h3><a name="lua_pushnil"><code>lua_pushnil</code></a></h3><p> 4493 <span class="apii">[-0, +1, –]</span> 4494 <pre>void lua_pushnil (lua_State *L);</pre> 4495 4496 <p> 4497 Pushes a nil value onto the stack. 4498 4499 4500 4501 4502 4503 <hr><h3><a name="lua_pushnumber"><code>lua_pushnumber</code></a></h3><p> 4504 <span class="apii">[-0, +1, –]</span> 4505 <pre>void lua_pushnumber (lua_State *L, lua_Number n);</pre> 4506 4507 <p> 4508 Pushes a float with value <code>n</code> onto the stack. 4509 4510 4511 4512 4513 4514 <hr><h3><a name="lua_pushstring"><code>lua_pushstring</code></a></h3><p> 4515 <span class="apii">[-0, +1, <em>m</em>]</span> 4516 <pre>const char *lua_pushstring (lua_State *L, const char *s);</pre> 4517 4518 <p> 4519 Pushes the zero-terminated string pointed to by <code>s</code> 4520 onto the stack. 4521 Lua makes (or reuses) an internal copy of the given string, 4522 so the memory at <code>s</code> can be freed or reused immediately after 4523 the function returns. 4524 4525 4526 <p> 4527 Returns a pointer to the internal copy of the string. 4528 4529 4530 <p> 4531 If <code>s</code> is <code>NULL</code>, pushes <b>nil</b> and returns <code>NULL</code>. 4532 4533 4534 4535 4536 4537 <hr><h3><a name="lua_pushthread"><code>lua_pushthread</code></a></h3><p> 4538 <span class="apii">[-0, +1, –]</span> 4539 <pre>int lua_pushthread (lua_State *L);</pre> 4540 4541 <p> 4542 Pushes the thread represented by <code>L</code> onto the stack. 4543 Returns 1 if this thread is the main thread of its state. 4544 4545 4546 4547 4548 4549 <hr><h3><a name="lua_pushvalue"><code>lua_pushvalue</code></a></h3><p> 4550 <span class="apii">[-0, +1, –]</span> 4551 <pre>void lua_pushvalue (lua_State *L, int index);</pre> 4552 4553 <p> 4554 Pushes a copy of the element at the given index 4555 onto the stack. 4556 4557 4558 4559 4560 4561 <hr><h3><a name="lua_pushvfstring"><code>lua_pushvfstring</code></a></h3><p> 4562 <span class="apii">[-0, +1, <em>m</em>]</span> 4563 <pre>const char *lua_pushvfstring (lua_State *L, 4564 const char *fmt, 4565 va_list argp);</pre> 4566 4567 <p> 4568 Equivalent to <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>, except that it receives a <code>va_list</code> 4569 instead of a variable number of arguments. 4570 4571 4572 4573 4574 4575 <hr><h3><a name="lua_rawequal"><code>lua_rawequal</code></a></h3><p> 4576 <span class="apii">[-0, +0, –]</span> 4577 <pre>int lua_rawequal (lua_State *L, int index1, int index2);</pre> 4578 4579 <p> 4580 Returns 1 if the two values in indices <code>index1</code> and 4581 <code>index2</code> are primitively equal 4582 (that is, without calling the <code>__eq</code> metamethod). 4583 Otherwise returns 0. 4584 Also returns 0 if any of the indices are not valid. 4585 4586 4587 4588 4589 4590 <hr><h3><a name="lua_rawget"><code>lua_rawget</code></a></h3><p> 4591 <span class="apii">[-1, +1, –]</span> 4592 <pre>int lua_rawget (lua_State *L, int index);</pre> 4593 4594 <p> 4595 Similar to <a href="#lua_gettable"><code>lua_gettable</code></a>, but does a raw access 4596 (i.e., without metamethods). 4597 4598 4599 4600 4601 4602 <hr><h3><a name="lua_rawgeti"><code>lua_rawgeti</code></a></h3><p> 4603 <span class="apii">[-0, +1, –]</span> 4604 <pre>int lua_rawgeti (lua_State *L, int index, lua_Integer n);</pre> 4605 4606 <p> 4607 Pushes onto the stack the value <code>t[n]</code>, 4608 where <code>t</code> is the table at the given index. 4609 The access is raw, 4610 that is, it does not invoke the <code>__index</code> metamethod. 4611 4612 4613 <p> 4614 Returns the type of the pushed value. 4615 4616 4617 4618 4619 4620 <hr><h3><a name="lua_rawgetp"><code>lua_rawgetp</code></a></h3><p> 4621 <span class="apii">[-0, +1, –]</span> 4622 <pre>int lua_rawgetp (lua_State *L, int index, const void *p);</pre> 4623 4624 <p> 4625 Pushes onto the stack the value <code>t[k]</code>, 4626 where <code>t</code> is the table at the given index and 4627 <code>k</code> is the pointer <code>p</code> represented as a light userdata. 4628 The access is raw; 4629 that is, it does not invoke the <code>__index</code> metamethod. 4630 4631 4632 <p> 4633 Returns the type of the pushed value. 4634 4635 4636 4637 4638 4639 <hr><h3><a name="lua_rawlen"><code>lua_rawlen</code></a></h3><p> 4640 <span class="apii">[-0, +0, –]</span> 4641 <pre>size_t lua_rawlen (lua_State *L, int index);</pre> 4642 4643 <p> 4644 Returns the raw "length" of the value at the given index: 4645 for strings, this is the string length; 4646 for tables, this is the result of the length operator ('<code>#</code>') 4647 with no metamethods; 4648 for userdata, this is the size of the block of memory allocated 4649 for the userdata; 4650 for other values, it is 0. 4651 4652 4653 4654 4655 4656 <hr><h3><a name="lua_rawset"><code>lua_rawset</code></a></h3><p> 4657 <span class="apii">[-2, +0, <em>m</em>]</span> 4658 <pre>void lua_rawset (lua_State *L, int index);</pre> 4659 4660 <p> 4661 Similar to <a href="#lua_settable"><code>lua_settable</code></a>, but does a raw assignment 4662 (i.e., without metamethods). 4663 4664 4665 4666 4667 4668 <hr><h3><a name="lua_rawseti"><code>lua_rawseti</code></a></h3><p> 4669 <span class="apii">[-1, +0, <em>m</em>]</span> 4670 <pre>void lua_rawseti (lua_State *L, int index, lua_Integer i);</pre> 4671 4672 <p> 4673 Does the equivalent of <code>t[i] = v</code>, 4674 where <code>t</code> is the table at the given index 4675 and <code>v</code> is the value at the top of the stack. 4676 4677 4678 <p> 4679 This function pops the value from the stack. 4680 The assignment is raw, 4681 that is, it does not invoke the <code>__newindex</code> metamethod. 4682 4683 4684 4685 4686 4687 <hr><h3><a name="lua_rawsetp"><code>lua_rawsetp</code></a></h3><p> 4688 <span class="apii">[-1, +0, <em>m</em>]</span> 4689 <pre>void lua_rawsetp (lua_State *L, int index, const void *p);</pre> 4690 4691 <p> 4692 Does the equivalent of <code>t[p] = v</code>, 4693 where <code>t</code> is the table at the given index, 4694 <code>p</code> is encoded as a light userdata, 4695 and <code>v</code> is the value at the top of the stack. 4696 4697 4698 <p> 4699 This function pops the value from the stack. 4700 The assignment is raw, 4701 that is, it does not invoke <code>__newindex</code> metamethod. 4702 4703 4704 4705 4706 4707 <hr><h3><a name="lua_Reader"><code>lua_Reader</code></a></h3> 4708 <pre>typedef const char * (*lua_Reader) (lua_State *L, 4709 void *data, 4710 size_t *size);</pre> 4711 4712 <p> 4713 The reader function used by <a href="#lua_load"><code>lua_load</code></a>. 4714 Every time it needs another piece of the chunk, 4715 <a href="#lua_load"><code>lua_load</code></a> calls the reader, 4716 passing along its <code>data</code> parameter. 4717 The reader must return a pointer to a block of memory 4718 with a new piece of the chunk 4719 and set <code>size</code> to the block size. 4720 The block must exist until the reader function is called again. 4721 To signal the end of the chunk, 4722 the reader must return <code>NULL</code> or set <code>size</code> to zero. 4723 The reader function may return pieces of any size greater than zero. 4724 4725 4726 4727 4728 4729 <hr><h3><a name="lua_register"><code>lua_register</code></a></h3><p> 4730 <span class="apii">[-0, +0, <em>e</em>]</span> 4731 <pre>void lua_register (lua_State *L, const char *name, lua_CFunction f);</pre> 4732 4733 <p> 4734 Sets the C function <code>f</code> as the new value of global <code>name</code>. 4735 It is defined as a macro: 4736 4737 <pre> 4738 #define lua_register(L,n,f) \ 4739 (lua_pushcfunction(L, f), lua_setglobal(L, n)) 4740 </pre> 4741 4742 4743 4744 4745 <hr><h3><a name="lua_remove"><code>lua_remove</code></a></h3><p> 4746 <span class="apii">[-1, +0, –]</span> 4747 <pre>void lua_remove (lua_State *L, int index);</pre> 4748 4749 <p> 4750 Removes the element at the given valid index, 4751 shifting down the elements above this index to fill the gap. 4752 This function cannot be called with a pseudo-index, 4753 because a pseudo-index is not an actual stack position. 4754 4755 4756 4757 4758 4759 <hr><h3><a name="lua_replace"><code>lua_replace</code></a></h3><p> 4760 <span class="apii">[-1, +0, –]</span> 4761 <pre>void lua_replace (lua_State *L, int index);</pre> 4762 4763 <p> 4764 Moves the top element into the given valid index 4765 without shifting any element 4766 (therefore replacing the value at that given index), 4767 and then pops the top element. 4768 4769 4770 4771 4772 4773 <hr><h3><a name="lua_resume"><code>lua_resume</code></a></h3><p> 4774 <span class="apii">[-?, +?, –]</span> 4775 <pre>int lua_resume (lua_State *L, lua_State *from, int nargs);</pre> 4776 4777 <p> 4778 Starts and resumes a coroutine in the given thread <code>L</code>. 4779 4780 4781 <p> 4782 To start a coroutine, 4783 you push onto the thread stack the main function plus any arguments; 4784 then you call <a href="#lua_resume"><code>lua_resume</code></a>, 4785 with <code>nargs</code> being the number of arguments. 4786 This call returns when the coroutine suspends or finishes its execution. 4787 When it returns, the stack contains all values passed to <a href="#lua_yield"><code>lua_yield</code></a>, 4788 or all values returned by the body function. 4789 <a href="#lua_resume"><code>lua_resume</code></a> returns 4790 <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the coroutine yields, 4791 <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> if the coroutine finishes its execution 4792 without errors, 4793 or an error code in case of errors (see <a href="#lua_pcall"><code>lua_pcall</code></a>). 4794 4795 4796 <p> 4797 In case of errors, 4798 the stack is not unwound, 4799 so you can use the debug API over it. 4800 The error object is on the top of the stack. 4801 4802 4803 <p> 4804 To resume a coroutine, 4805 you remove any results from the last <a href="#lua_yield"><code>lua_yield</code></a>, 4806 put on its stack only the values to 4807 be passed as results from <code>yield</code>, 4808 and then call <a href="#lua_resume"><code>lua_resume</code></a>. 4809 4810 4811 <p> 4812 The parameter <code>from</code> represents the coroutine that is resuming <code>L</code>. 4813 If there is no such coroutine, 4814 this parameter can be <code>NULL</code>. 4815 4816 4817 4818 4819 4820 <hr><h3><a name="lua_rotate"><code>lua_rotate</code></a></h3><p> 4821 <span class="apii">[-0, +0, –]</span> 4822 <pre>void lua_rotate (lua_State *L, int idx, int n);</pre> 4823 4824 <p> 4825 Rotates the stack elements between the valid index <code>idx</code> 4826 and the top of the stack. 4827 The elements are rotated <code>n</code> positions in the direction of the top, 4828 for a positive <code>n</code>, 4829 or <code>-n</code> positions in the direction of the bottom, 4830 for a negative <code>n</code>. 4831 The absolute value of <code>n</code> must not be greater than the size 4832 of the slice being rotated. 4833 This function cannot be called with a pseudo-index, 4834 because a pseudo-index is not an actual stack position. 4835 4836 4837 4838 4839 4840 <hr><h3><a name="lua_setallocf"><code>lua_setallocf</code></a></h3><p> 4841 <span class="apii">[-0, +0, –]</span> 4842 <pre>void lua_setallocf (lua_State *L, lua_Alloc f, void *ud);</pre> 4843 4844 <p> 4845 Changes the allocator function of a given state to <code>f</code> 4846 with user data <code>ud</code>. 4847 4848 4849 4850 4851 4852 <hr><h3><a name="lua_setfield"><code>lua_setfield</code></a></h3><p> 4853 <span class="apii">[-1, +0, <em>e</em>]</span> 4854 <pre>void lua_setfield (lua_State *L, int index, const char *k);</pre> 4855 4856 <p> 4857 Does the equivalent to <code>t[k] = v</code>, 4858 where <code>t</code> is the value at the given index 4859 and <code>v</code> is the value at the top of the stack. 4860 4861 4862 <p> 4863 This function pops the value from the stack. 4864 As in Lua, this function may trigger a metamethod 4865 for the "newindex" event (see <a href="#2.4">§2.4</a>). 4866 4867 4868 4869 4870 4871 <hr><h3><a name="lua_setglobal"><code>lua_setglobal</code></a></h3><p> 4872 <span class="apii">[-1, +0, <em>e</em>]</span> 4873 <pre>void lua_setglobal (lua_State *L, const char *name);</pre> 4874 4875 <p> 4876 Pops a value from the stack and 4877 sets it as the new value of global <code>name</code>. 4878 4879 4880 4881 4882 4883 <hr><h3><a name="lua_seti"><code>lua_seti</code></a></h3><p> 4884 <span class="apii">[-1, +0, <em>e</em>]</span> 4885 <pre>void lua_seti (lua_State *L, int index, lua_Integer n);</pre> 4886 4887 <p> 4888 Does the equivalent to <code>t[n] = v</code>, 4889 where <code>t</code> is the value at the given index 4890 and <code>v</code> is the value at the top of the stack. 4891 4892 4893 <p> 4894 This function pops the value from the stack. 4895 As in Lua, this function may trigger a metamethod 4896 for the "newindex" event (see <a href="#2.4">§2.4</a>). 4897 4898 4899 4900 4901 4902 <hr><h3><a name="lua_setmetatable"><code>lua_setmetatable</code></a></h3><p> 4903 <span class="apii">[-1, +0, –]</span> 4904 <pre>void lua_setmetatable (lua_State *L, int index);</pre> 4905 4906 <p> 4907 Pops a table from the stack and 4908 sets it as the new metatable for the value at the given index. 4909 4910 4911 4912 4913 4914 <hr><h3><a name="lua_settable"><code>lua_settable</code></a></h3><p> 4915 <span class="apii">[-2, +0, <em>e</em>]</span> 4916 <pre>void lua_settable (lua_State *L, int index);</pre> 4917 4918 <p> 4919 Does the equivalent to <code>t[k] = v</code>, 4920 where <code>t</code> is the value at the given index, 4921 <code>v</code> is the value at the top of the stack, 4922 and <code>k</code> is the value just below the top. 4923 4924 4925 <p> 4926 This function pops both the key and the value from the stack. 4927 As in Lua, this function may trigger a metamethod 4928 for the "newindex" event (see <a href="#2.4">§2.4</a>). 4929 4930 4931 4932 4933 4934 <hr><h3><a name="lua_settop"><code>lua_settop</code></a></h3><p> 4935 <span class="apii">[-?, +?, –]</span> 4936 <pre>void lua_settop (lua_State *L, int index);</pre> 4937 4938 <p> 4939 Accepts any index, or 0, 4940 and sets the stack top to this index. 4941 If the new top is larger than the old one, 4942 then the new elements are filled with <b>nil</b>. 4943 If <code>index</code> is 0, then all stack elements are removed. 4944 4945 4946 4947 4948 4949 <hr><h3><a name="lua_setuservalue"><code>lua_setuservalue</code></a></h3><p> 4950 <span class="apii">[-1, +0, –]</span> 4951 <pre>void lua_setuservalue (lua_State *L, int index);</pre> 4952 4953 <p> 4954 Pops a value from the stack and sets it as 4955 the new value associated to the full userdata at the given index. 4956 4957 4958 4959 4960 4961 <hr><h3><a name="lua_State"><code>lua_State</code></a></h3> 4962 <pre>typedef struct lua_State lua_State;</pre> 4963 4964 <p> 4965 An opaque structure that points to a thread and indirectly 4966 (through the thread) to the whole state of a Lua interpreter. 4967 The Lua library is fully reentrant: 4968 it has no global variables. 4969 All information about a state is accessible through this structure. 4970 4971 4972 <p> 4973 A pointer to this structure must be passed as the first argument to 4974 every function in the library, except to <a href="#lua_newstate"><code>lua_newstate</code></a>, 4975 which creates a Lua state from scratch. 4976 4977 4978 4979 4980 4981 <hr><h3><a name="lua_status"><code>lua_status</code></a></h3><p> 4982 <span class="apii">[-0, +0, –]</span> 4983 <pre>int lua_status (lua_State *L);</pre> 4984 4985 <p> 4986 Returns the status of the thread <code>L</code>. 4987 4988 4989 <p> 4990 The status can be 0 (<a href="#pdf-LUA_OK"><code>LUA_OK</code></a>) for a normal thread, 4991 an error code if the thread finished the execution 4992 of a <a href="#lua_resume"><code>lua_resume</code></a> with an error, 4993 or <a name="pdf-LUA_YIELD"><code>LUA_YIELD</code></a> if the thread is suspended. 4994 4995 4996 <p> 4997 You can only call functions in threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a>. 4998 You can resume threads with status <a href="#pdf-LUA_OK"><code>LUA_OK</code></a> 4999 (to start a new coroutine) or <a href="#pdf-LUA_YIELD"><code>LUA_YIELD</code></a> 5000 (to resume a coroutine). 5001 5002 5003 5004 5005 5006 <hr><h3><a name="lua_stringtonumber"><code>lua_stringtonumber</code></a></h3><p> 5007 <span class="apii">[-0, +1, –]</span> 5008 <pre>size_t lua_stringtonumber (lua_State *L, const char *s);</pre> 5009 5010 <p> 5011 Converts the zero-terminated string <code>s</code> to a number, 5012 pushes that number into the stack, 5013 and returns the total size of the string, 5014 that is, its length plus one. 5015 The conversion can result in an integer or a float, 5016 according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>). 5017 The string may have leading and trailing spaces and a sign. 5018 If the string is not a valid numeral, 5019 returns 0 and pushes nothing. 5020 (Note that the result can be used as a boolean, 5021 true if the conversion succeeds.) 5022 5023 5024 5025 5026 5027 <hr><h3><a name="lua_toboolean"><code>lua_toboolean</code></a></h3><p> 5028 <span class="apii">[-0, +0, –]</span> 5029 <pre>int lua_toboolean (lua_State *L, int index);</pre> 5030 5031 <p> 5032 Converts the Lua value at the given index to a C boolean 5033 value (0 or 1). 5034 Like all tests in Lua, 5035 <a href="#lua_toboolean"><code>lua_toboolean</code></a> returns true for any Lua value 5036 different from <b>false</b> and <b>nil</b>; 5037 otherwise it returns false. 5038 (If you want to accept only actual boolean values, 5039 use <a href="#lua_isboolean"><code>lua_isboolean</code></a> to test the value's type.) 5040 5041 5042 5043 5044 5045 <hr><h3><a name="lua_tocfunction"><code>lua_tocfunction</code></a></h3><p> 5046 <span class="apii">[-0, +0, –]</span> 5047 <pre>lua_CFunction lua_tocfunction (lua_State *L, int index);</pre> 5048 5049 <p> 5050 Converts a value at the given index to a C function. 5051 That value must be a C function; 5052 otherwise, returns <code>NULL</code>. 5053 5054 5055 5056 5057 5058 <hr><h3><a name="lua_tointeger"><code>lua_tointeger</code></a></h3><p> 5059 <span class="apii">[-0, +0, –]</span> 5060 <pre>lua_Integer lua_tointeger (lua_State *L, int index);</pre> 5061 5062 <p> 5063 Equivalent to <a href="#lua_tointegerx"><code>lua_tointegerx</code></a> with <code>isnum</code> equal to <code>NULL</code>. 5064 5065 5066 5067 5068 5069 <hr><h3><a name="lua_tointegerx"><code>lua_tointegerx</code></a></h3><p> 5070 <span class="apii">[-0, +0, –]</span> 5071 <pre>lua_Integer lua_tointegerx (lua_State *L, int index, int *isnum);</pre> 5072 5073 <p> 5074 Converts the Lua value at the given index 5075 to the signed integral type <a href="#lua_Integer"><code>lua_Integer</code></a>. 5076 The Lua value must be an integer, 5077 or a number or string convertible to an integer (see <a href="#3.4.3">§3.4.3</a>); 5078 otherwise, <code>lua_tointegerx</code> returns 0. 5079 5080 5081 <p> 5082 If <code>isnum</code> is not <code>NULL</code>, 5083 its referent is assigned a boolean value that 5084 indicates whether the operation succeeded. 5085 5086 5087 5088 5089 5090 <hr><h3><a name="lua_tolstring"><code>lua_tolstring</code></a></h3><p> 5091 <span class="apii">[-0, +0, <em>m</em>]</span> 5092 <pre>const char *lua_tolstring (lua_State *L, int index, size_t *len);</pre> 5093 5094 <p> 5095 Converts the Lua value at the given index to a C string. 5096 If <code>len</code> is not <code>NULL</code>, 5097 it sets <code>*len</code> with the string length. 5098 The Lua value must be a string or a number; 5099 otherwise, the function returns <code>NULL</code>. 5100 If the value is a number, 5101 then <code>lua_tolstring</code> also 5102 <em>changes the actual value in the stack to a string</em>. 5103 (This change confuses <a href="#lua_next"><code>lua_next</code></a> 5104 when <code>lua_tolstring</code> is applied to keys during a table traversal.) 5105 5106 5107 <p> 5108 <code>lua_tolstring</code> returns a pointer 5109 to a string inside the Lua state. 5110 This string always has a zero ('<code>\0</code>') 5111 after its last character (as in C), 5112 but can contain other zeros in its body. 5113 5114 5115 <p> 5116 Because Lua has garbage collection, 5117 there is no guarantee that the pointer returned by <code>lua_tolstring</code> 5118 will be valid after the corresponding Lua value is removed from the stack. 5119 5120 5121 5122 5123 5124 <hr><h3><a name="lua_tonumber"><code>lua_tonumber</code></a></h3><p> 5125 <span class="apii">[-0, +0, –]</span> 5126 <pre>lua_Number lua_tonumber (lua_State *L, int index);</pre> 5127 5128 <p> 5129 Equivalent to <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> with <code>isnum</code> equal to <code>NULL</code>. 5130 5131 5132 5133 5134 5135 <hr><h3><a name="lua_tonumberx"><code>lua_tonumberx</code></a></h3><p> 5136 <span class="apii">[-0, +0, –]</span> 5137 <pre>lua_Number lua_tonumberx (lua_State *L, int index, int *isnum);</pre> 5138 5139 <p> 5140 Converts the Lua value at the given index 5141 to the C type <a href="#lua_Number"><code>lua_Number</code></a> (see <a href="#lua_Number"><code>lua_Number</code></a>). 5142 The Lua value must be a number or a string convertible to a number 5143 (see <a href="#3.4.3">§3.4.3</a>); 5144 otherwise, <a href="#lua_tonumberx"><code>lua_tonumberx</code></a> returns 0. 5145 5146 5147 <p> 5148 If <code>isnum</code> is not <code>NULL</code>, 5149 its referent is assigned a boolean value that 5150 indicates whether the operation succeeded. 5151 5152 5153 5154 5155 5156 <hr><h3><a name="lua_topointer"><code>lua_topointer</code></a></h3><p> 5157 <span class="apii">[-0, +0, –]</span> 5158 <pre>const void *lua_topointer (lua_State *L, int index);</pre> 5159 5160 <p> 5161 Converts the value at the given index to a generic 5162 C pointer (<code>void*</code>). 5163 The value can be a userdata, a table, a thread, or a function; 5164 otherwise, <code>lua_topointer</code> returns <code>NULL</code>. 5165 Different objects will give different pointers. 5166 There is no way to convert the pointer back to its original value. 5167 5168 5169 <p> 5170 Typically this function is used only for hashing and debug information. 5171 5172 5173 5174 5175 5176 <hr><h3><a name="lua_tostring"><code>lua_tostring</code></a></h3><p> 5177 <span class="apii">[-0, +0, <em>m</em>]</span> 5178 <pre>const char *lua_tostring (lua_State *L, int index);</pre> 5179 5180 <p> 5181 Equivalent to <a href="#lua_tolstring"><code>lua_tolstring</code></a> with <code>len</code> equal to <code>NULL</code>. 5182 5183 5184 5185 5186 5187 <hr><h3><a name="lua_tothread"><code>lua_tothread</code></a></h3><p> 5188 <span class="apii">[-0, +0, –]</span> 5189 <pre>lua_State *lua_tothread (lua_State *L, int index);</pre> 5190 5191 <p> 5192 Converts the value at the given index to a Lua thread 5193 (represented as <code>lua_State*</code>). 5194 This value must be a thread; 5195 otherwise, the function returns <code>NULL</code>. 5196 5197 5198 5199 5200 5201 <hr><h3><a name="lua_touserdata"><code>lua_touserdata</code></a></h3><p> 5202 <span class="apii">[-0, +0, –]</span> 5203 <pre>void *lua_touserdata (lua_State *L, int index);</pre> 5204 5205 <p> 5206 If the value at the given index is a full userdata, 5207 returns its block address. 5208 If the value is a light userdata, 5209 returns its pointer. 5210 Otherwise, returns <code>NULL</code>. 5211 5212 5213 5214 5215 5216 <hr><h3><a name="lua_type"><code>lua_type</code></a></h3><p> 5217 <span class="apii">[-0, +0, –]</span> 5218 <pre>int lua_type (lua_State *L, int index);</pre> 5219 5220 <p> 5221 Returns the type of the value in the given valid index, 5222 or <code>LUA_TNONE</code> for a non-valid (but acceptable) index. 5223 The types returned by <a href="#lua_type"><code>lua_type</code></a> are coded by the following constants 5224 defined in <code>lua.h</code>: 5225 <a name="pdf-LUA_TNIL"><code>LUA_TNIL</code></a> (0), 5226 <a name="pdf-LUA_TNUMBER"><code>LUA_TNUMBER</code></a>, 5227 <a name="pdf-LUA_TBOOLEAN"><code>LUA_TBOOLEAN</code></a>, 5228 <a name="pdf-LUA_TSTRING"><code>LUA_TSTRING</code></a>, 5229 <a name="pdf-LUA_TTABLE"><code>LUA_TTABLE</code></a>, 5230 <a name="pdf-LUA_TFUNCTION"><code>LUA_TFUNCTION</code></a>, 5231 <a name="pdf-LUA_TUSERDATA"><code>LUA_TUSERDATA</code></a>, 5232 <a name="pdf-LUA_TTHREAD"><code>LUA_TTHREAD</code></a>, 5233 and 5234 <a name="pdf-LUA_TLIGHTUSERDATA"><code>LUA_TLIGHTUSERDATA</code></a>. 5235 5236 5237 5238 5239 5240 <hr><h3><a name="lua_typename"><code>lua_typename</code></a></h3><p> 5241 <span class="apii">[-0, +0, –]</span> 5242 <pre>const char *lua_typename (lua_State *L, int tp);</pre> 5243 5244 <p> 5245 Returns the name of the type encoded by the value <code>tp</code>, 5246 which must be one the values returned by <a href="#lua_type"><code>lua_type</code></a>. 5247 5248 5249 5250 5251 5252 <hr><h3><a name="lua_Unsigned"><code>lua_Unsigned</code></a></h3> 5253 <pre>typedef ... lua_Unsigned;</pre> 5254 5255 <p> 5256 The unsigned version of <a href="#lua_Integer"><code>lua_Integer</code></a>. 5257 5258 5259 5260 5261 5262 <hr><h3><a name="lua_upvalueindex"><code>lua_upvalueindex</code></a></h3><p> 5263 <span class="apii">[-0, +0, –]</span> 5264 <pre>int lua_upvalueindex (int i);</pre> 5265 5266 <p> 5267 Returns the pseudo-index that represents the <code>i</code>-th upvalue of 5268 the running function (see <a href="#4.4">§4.4</a>). 5269 5270 5271 5272 5273 5274 <hr><h3><a name="lua_version"><code>lua_version</code></a></h3><p> 5275 <span class="apii">[-0, +0, –]</span> 5276 <pre>const lua_Number *lua_version (lua_State *L);</pre> 5277 5278 <p> 5279 Returns the address of the version number 5280 (a C static variable) 5281 stored in the Lua core. 5282 When called with a valid <a href="#lua_State"><code>lua_State</code></a>, 5283 returns the address of the version used to create that state. 5284 When called with <code>NULL</code>, 5285 returns the address of the version running the call. 5286 5287 5288 5289 5290 5291 <hr><h3><a name="lua_Writer"><code>lua_Writer</code></a></h3> 5292 <pre>typedef int (*lua_Writer) (lua_State *L, 5293 const void* p, 5294 size_t sz, 5295 void* ud);</pre> 5296 5297 <p> 5298 The type of the writer function used by <a href="#lua_dump"><code>lua_dump</code></a>. 5299 Every time it produces another piece of chunk, 5300 <a href="#lua_dump"><code>lua_dump</code></a> calls the writer, 5301 passing along the buffer to be written (<code>p</code>), 5302 its size (<code>sz</code>), 5303 and the <code>data</code> parameter supplied to <a href="#lua_dump"><code>lua_dump</code></a>. 5304 5305 5306 <p> 5307 The writer returns an error code: 5308 0 means no errors; 5309 any other value means an error and stops <a href="#lua_dump"><code>lua_dump</code></a> from 5310 calling the writer again. 5311 5312 5313 5314 5315 5316 <hr><h3><a name="lua_xmove"><code>lua_xmove</code></a></h3><p> 5317 <span class="apii">[-?, +?, –]</span> 5318 <pre>void lua_xmove (lua_State *from, lua_State *to, int n);</pre> 5319 5320 <p> 5321 Exchange values between different threads of the same state. 5322 5323 5324 <p> 5325 This function pops <code>n</code> values from the stack <code>from</code>, 5326 and pushes them onto the stack <code>to</code>. 5327 5328 5329 5330 5331 5332 <hr><h3><a name="lua_yield"><code>lua_yield</code></a></h3><p> 5333 <span class="apii">[-?, +?, <em>e</em>]</span> 5334 <pre>int lua_yield (lua_State *L, int nresults);</pre> 5335 5336 <p> 5337 This function is equivalent to <a href="#lua_yieldk"><code>lua_yieldk</code></a>, 5338 but it has no continuation (see <a href="#4.7">§4.7</a>). 5339 Therefore, when the thread resumes, 5340 it continues the function that called 5341 the function calling <code>lua_yield</code>. 5342 5343 5344 5345 5346 5347 <hr><h3><a name="lua_yieldk"><code>lua_yieldk</code></a></h3><p> 5348 <span class="apii">[-?, +?, <em>e</em>]</span> 5349 <pre>int lua_yieldk (lua_State *L, 5350 int nresults, 5351 lua_KContext ctx, 5352 lua_KFunction k);</pre> 5353 5354 <p> 5355 Yields a coroutine (thread). 5356 5357 5358 <p> 5359 When a C function calls <a href="#lua_yieldk"><code>lua_yieldk</code></a>, 5360 the running coroutine suspends its execution, 5361 and the call to <a href="#lua_resume"><code>lua_resume</code></a> that started this coroutine returns. 5362 The parameter <code>nresults</code> is the number of values from the stack 5363 that will be passed as results to <a href="#lua_resume"><code>lua_resume</code></a>. 5364 5365 5366 <p> 5367 When the coroutine is resumed again, 5368 Lua calls the given continuation function <code>k</code> to continue 5369 the execution of the C function that yielded (see <a href="#4.7">§4.7</a>). 5370 This continuation function receives the same stack 5371 from the previous function, 5372 with the <code>n</code> results removed and 5373 replaced by the arguments passed to <a href="#lua_resume"><code>lua_resume</code></a>. 5374 Moreover, 5375 the continuation function receives the value <code>ctx</code> 5376 that was passed to <a href="#lua_yieldk"><code>lua_yieldk</code></a>. 5377 5378 5379 <p> 5380 Usually, this function does not return; 5381 when the coroutine eventually resumes, 5382 it continues executing the continuation function. 5383 However, there is one special case, 5384 which is when this function is called 5385 from inside a line or a count hook (see <a href="#4.9">§4.9</a>). 5386 In that case, <code>lua_yieldk</code> should be called with no continuation 5387 (probably in the form of <a href="#lua_yield"><code>lua_yield</code></a>) and no results, 5388 and the hook should return immediately after the call. 5389 Lua will yield and, 5390 when the coroutine resumes again, 5391 it will continue the normal execution 5392 of the (Lua) function that triggered the hook. 5393 5394 5395 <p> 5396 This function can raise an error if it is called from a thread 5397 with a pending C call with no continuation function, 5398 or it is called from a thread that is not running inside a resume 5399 (e.g., the main thread). 5400 5401 5402 5403 5404 5405 5406 5407 <h2>4.9 – <a name="4.9">The Debug Interface</a></h2> 5408 5409 <p> 5410 Lua has no built-in debugging facilities. 5411 Instead, it offers a special interface 5412 by means of functions and <em>hooks</em>. 5413 This interface allows the construction of different 5414 kinds of debuggers, profilers, and other tools 5415 that need "inside information" from the interpreter. 5416 5417 5418 5419 <hr><h3><a name="lua_Debug"><code>lua_Debug</code></a></h3> 5420 <pre>typedef struct lua_Debug { 5421 int event; 5422 const char *name; /* (n) */ 5423 const char *namewhat; /* (n) */ 5424 const char *what; /* (S) */ 5425 const char *source; /* (S) */ 5426 int currentline; /* (l) */ 5427 int linedefined; /* (S) */ 5428 int lastlinedefined; /* (S) */ 5429 unsigned char nups; /* (u) number of upvalues */ 5430 unsigned char nparams; /* (u) number of parameters */ 5431 char isvararg; /* (u) */ 5432 char istailcall; /* (t) */ 5433 char short_src[LUA_IDSIZE]; /* (S) */ 5434 /* private part */ 5435 <em>other fields</em> 5436 } lua_Debug;</pre> 5437 5438 <p> 5439 A structure used to carry different pieces of 5440 information about a function or an activation record. 5441 <a href="#lua_getstack"><code>lua_getstack</code></a> fills only the private part 5442 of this structure, for later use. 5443 To fill the other fields of <a href="#lua_Debug"><code>lua_Debug</code></a> with useful information, 5444 call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. 5445 5446 5447 <p> 5448 The fields of <a href="#lua_Debug"><code>lua_Debug</code></a> have the following meaning: 5449 5450 <ul> 5451 5452 <li><b><code>source</code>: </b> 5453 the name of the chunk that created the function. 5454 If <code>source</code> starts with a '<code>@</code>', 5455 it means that the function was defined in a file where 5456 the file name follows the '<code>@</code>'. 5457 If <code>source</code> starts with a '<code>=</code>', 5458 the remainder of its contents describe the source in a user-dependent manner. 5459 Otherwise, 5460 the function was defined in a string where 5461 <code>source</code> is that string. 5462 </li> 5463 5464 <li><b><code>short_src</code>: </b> 5465 a "printable" version of <code>source</code>, to be used in error messages. 5466 </li> 5467 5468 <li><b><code>linedefined</code>: </b> 5469 the line number where the definition of the function starts. 5470 </li> 5471 5472 <li><b><code>lastlinedefined</code>: </b> 5473 the line number where the definition of the function ends. 5474 </li> 5475 5476 <li><b><code>what</code>: </b> 5477 the string <code>"Lua"</code> if the function is a Lua function, 5478 <code>"C"</code> if it is a C function, 5479 <code>"main"</code> if it is the main part of a chunk. 5480 </li> 5481 5482 <li><b><code>currentline</code>: </b> 5483 the current line where the given function is executing. 5484 When no line information is available, 5485 <code>currentline</code> is set to -1. 5486 </li> 5487 5488 <li><b><code>name</code>: </b> 5489 a reasonable name for the given function. 5490 Because functions in Lua are first-class values, 5491 they do not have a fixed name: 5492 some functions can be the value of multiple global variables, 5493 while others can be stored only in a table field. 5494 The <code>lua_getinfo</code> function checks how the function was 5495 called to find a suitable name. 5496 If it cannot find a name, 5497 then <code>name</code> is set to <code>NULL</code>. 5498 </li> 5499 5500 <li><b><code>namewhat</code>: </b> 5501 explains the <code>name</code> field. 5502 The value of <code>namewhat</code> can be 5503 <code>"global"</code>, <code>"local"</code>, <code>"method"</code>, 5504 <code>"field"</code>, <code>"upvalue"</code>, or <code>""</code> (the empty string), 5505 according to how the function was called. 5506 (Lua uses the empty string when no other option seems to apply.) 5507 </li> 5508 5509 <li><b><code>istailcall</code>: </b> 5510 true if this function invocation was called by a tail call. 5511 In this case, the caller of this level is not in the stack. 5512 </li> 5513 5514 <li><b><code>nups</code>: </b> 5515 the number of upvalues of the function. 5516 </li> 5517 5518 <li><b><code>nparams</code>: </b> 5519 the number of fixed parameters of the function 5520 (always 0 for C functions). 5521 </li> 5522 5523 <li><b><code>isvararg</code>: </b> 5524 true if the function is a vararg function 5525 (always true for C functions). 5526 </li> 5527 5528 </ul> 5529 5530 5531 5532 5533 <hr><h3><a name="lua_gethook"><code>lua_gethook</code></a></h3><p> 5534 <span class="apii">[-0, +0, –]</span> 5535 <pre>lua_Hook lua_gethook (lua_State *L);</pre> 5536 5537 <p> 5538 Returns the current hook function. 5539 5540 5541 5542 5543 5544 <hr><h3><a name="lua_gethookcount"><code>lua_gethookcount</code></a></h3><p> 5545 <span class="apii">[-0, +0, –]</span> 5546 <pre>int lua_gethookcount (lua_State *L);</pre> 5547 5548 <p> 5549 Returns the current hook count. 5550 5551 5552 5553 5554 5555 <hr><h3><a name="lua_gethookmask"><code>lua_gethookmask</code></a></h3><p> 5556 <span class="apii">[-0, +0, –]</span> 5557 <pre>int lua_gethookmask (lua_State *L);</pre> 5558 5559 <p> 5560 Returns the current hook mask. 5561 5562 5563 5564 5565 5566 <hr><h3><a name="lua_getinfo"><code>lua_getinfo</code></a></h3><p> 5567 <span class="apii">[-(0|1), +(0|1|2), <em>e</em>]</span> 5568 <pre>int lua_getinfo (lua_State *L, const char *what, lua_Debug *ar);</pre> 5569 5570 <p> 5571 Gets information about a specific function or function invocation. 5572 5573 5574 <p> 5575 To get information about a function invocation, 5576 the parameter <code>ar</code> must be a valid activation record that was 5577 filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or 5578 given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). 5579 5580 5581 <p> 5582 To get information about a function, you push it onto the stack 5583 and start the <code>what</code> string with the character '<code>></code>'. 5584 (In that case, 5585 <code>lua_getinfo</code> pops the function from the top of the stack.) 5586 For instance, to know in which line a function <code>f</code> was defined, 5587 you can write the following code: 5588 5589 <pre> 5590 lua_Debug ar; 5591 lua_getglobal(L, "f"); /* get global 'f' */ 5592 lua_getinfo(L, ">S", &ar); 5593 printf("%d\n", ar.linedefined); 5594 </pre> 5595 5596 <p> 5597 Each character in the string <code>what</code> 5598 selects some fields of the structure <code>ar</code> to be filled or 5599 a value to be pushed on the stack: 5600 5601 <ul> 5602 5603 <li><b>'<code>n</code>': </b> fills in the field <code>name</code> and <code>namewhat</code>; 5604 </li> 5605 5606 <li><b>'<code>S</code>': </b> 5607 fills in the fields <code>source</code>, <code>short_src</code>, 5608 <code>linedefined</code>, <code>lastlinedefined</code>, and <code>what</code>; 5609 </li> 5610 5611 <li><b>'<code>l</code>': </b> fills in the field <code>currentline</code>; 5612 </li> 5613 5614 <li><b>'<code>t</code>': </b> fills in the field <code>istailcall</code>; 5615 </li> 5616 5617 <li><b>'<code>u</code>': </b> fills in the fields 5618 <code>nups</code>, <code>nparams</code>, and <code>isvararg</code>; 5619 </li> 5620 5621 <li><b>'<code>f</code>': </b> 5622 pushes onto the stack the function that is 5623 running at the given level; 5624 </li> 5625 5626 <li><b>'<code>L</code>': </b> 5627 pushes onto the stack a table whose indices are the 5628 numbers of the lines that are valid on the function. 5629 (A <em>valid line</em> is a line with some associated code, 5630 that is, a line where you can put a break point. 5631 Non-valid lines include empty lines and comments.) 5632 5633 5634 <p> 5635 If this option is given together with option '<code>f</code>', 5636 its table is pushed after the function. 5637 </li> 5638 5639 </ul> 5640 5641 <p> 5642 This function returns 0 on error 5643 (for instance, an invalid option in <code>what</code>). 5644 5645 5646 5647 5648 5649 <hr><h3><a name="lua_getlocal"><code>lua_getlocal</code></a></h3><p> 5650 <span class="apii">[-0, +(0|1), –]</span> 5651 <pre>const char *lua_getlocal (lua_State *L, const lua_Debug *ar, int n);</pre> 5652 5653 <p> 5654 Gets information about a local variable of 5655 a given activation record or a given function. 5656 5657 5658 <p> 5659 In the first case, 5660 the parameter <code>ar</code> must be a valid activation record that was 5661 filled by a previous call to <a href="#lua_getstack"><code>lua_getstack</code></a> or 5662 given as argument to a hook (see <a href="#lua_Hook"><code>lua_Hook</code></a>). 5663 The index <code>n</code> selects which local variable to inspect; 5664 see <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for details about variable indices 5665 and names. 5666 5667 5668 <p> 5669 <a href="#lua_getlocal"><code>lua_getlocal</code></a> pushes the variable's value onto the stack 5670 and returns its name. 5671 5672 5673 <p> 5674 In the second case, <code>ar</code> must be <code>NULL</code> and the function 5675 to be inspected must be at the top of the stack. 5676 In this case, only parameters of Lua functions are visible 5677 (as there is no information about what variables are active) 5678 and no values are pushed onto the stack. 5679 5680 5681 <p> 5682 Returns <code>NULL</code> (and pushes nothing) 5683 when the index is greater than 5684 the number of active local variables. 5685 5686 5687 5688 5689 5690 <hr><h3><a name="lua_getstack"><code>lua_getstack</code></a></h3><p> 5691 <span class="apii">[-0, +0, –]</span> 5692 <pre>int lua_getstack (lua_State *L, int level, lua_Debug *ar);</pre> 5693 5694 <p> 5695 Gets information about the interpreter runtime stack. 5696 5697 5698 <p> 5699 This function fills parts of a <a href="#lua_Debug"><code>lua_Debug</code></a> structure with 5700 an identification of the <em>activation record</em> 5701 of the function executing at a given level. 5702 Level 0 is the current running function, 5703 whereas level <em>n+1</em> is the function that has called level <em>n</em> 5704 (except for tail calls, which do not count on the stack). 5705 When there are no errors, <a href="#lua_getstack"><code>lua_getstack</code></a> returns 1; 5706 when called with a level greater than the stack depth, 5707 it returns 0. 5708 5709 5710 5711 5712 5713 <hr><h3><a name="lua_getupvalue"><code>lua_getupvalue</code></a></h3><p> 5714 <span class="apii">[-0, +(0|1), –]</span> 5715 <pre>const char *lua_getupvalue (lua_State *L, int funcindex, int n);</pre> 5716 5717 <p> 5718 Gets information about the <code>n</code>-th upvalue 5719 of the closure at index <code>funcindex</code>. 5720 It pushes the upvalue's value onto the stack 5721 and returns its name. 5722 Returns <code>NULL</code> (and pushes nothing) 5723 when the index <code>n</code> is greater than the number of upvalues. 5724 5725 5726 <p> 5727 For C functions, this function uses the empty string <code>""</code> 5728 as a name for all upvalues. 5729 (For Lua functions, 5730 upvalues are the external local variables that the function uses, 5731 and that are consequently included in its closure.) 5732 5733 5734 <p> 5735 Upvalues have no particular order, 5736 as they are active through the whole function. 5737 They are numbered in an arbitrary order. 5738 5739 5740 5741 5742 5743 <hr><h3><a name="lua_Hook"><code>lua_Hook</code></a></h3> 5744 <pre>typedef void (*lua_Hook) (lua_State *L, lua_Debug *ar);</pre> 5745 5746 <p> 5747 Type for debugging hook functions. 5748 5749 5750 <p> 5751 Whenever a hook is called, its <code>ar</code> argument has its field 5752 <code>event</code> set to the specific event that triggered the hook. 5753 Lua identifies these events with the following constants: 5754 <a name="pdf-LUA_HOOKCALL"><code>LUA_HOOKCALL</code></a>, <a name="pdf-LUA_HOOKRET"><code>LUA_HOOKRET</code></a>, 5755 <a name="pdf-LUA_HOOKTAILCALL"><code>LUA_HOOKTAILCALL</code></a>, <a name="pdf-LUA_HOOKLINE"><code>LUA_HOOKLINE</code></a>, 5756 and <a name="pdf-LUA_HOOKCOUNT"><code>LUA_HOOKCOUNT</code></a>. 5757 Moreover, for line events, the field <code>currentline</code> is also set. 5758 To get the value of any other field in <code>ar</code>, 5759 the hook must call <a href="#lua_getinfo"><code>lua_getinfo</code></a>. 5760 5761 5762 <p> 5763 For call events, <code>event</code> can be <code>LUA_HOOKCALL</code>, 5764 the normal value, or <code>LUA_HOOKTAILCALL</code>, for a tail call; 5765 in this case, there will be no corresponding return event. 5766 5767 5768 <p> 5769 While Lua is running a hook, it disables other calls to hooks. 5770 Therefore, if a hook calls back Lua to execute a function or a chunk, 5771 this execution occurs without any calls to hooks. 5772 5773 5774 <p> 5775 Hook functions cannot have continuations, 5776 that is, they cannot call <a href="#lua_yieldk"><code>lua_yieldk</code></a>, 5777 <a href="#lua_pcallk"><code>lua_pcallk</code></a>, or <a href="#lua_callk"><code>lua_callk</code></a> with a non-null <code>k</code>. 5778 5779 5780 <p> 5781 Hook functions can yield under the following conditions: 5782 Only count and line events can yield; 5783 to yield, a hook function must finish its execution 5784 calling <a href="#lua_yield"><code>lua_yield</code></a> with <code>nresults</code> equal to zero 5785 (that is, with no values). 5786 5787 5788 5789 5790 5791 <hr><h3><a name="lua_sethook"><code>lua_sethook</code></a></h3><p> 5792 <span class="apii">[-0, +0, –]</span> 5793 <pre>void lua_sethook (lua_State *L, lua_Hook f, int mask, int count);</pre> 5794 5795 <p> 5796 Sets the debugging hook function. 5797 5798 5799 <p> 5800 Argument <code>f</code> is the hook function. 5801 <code>mask</code> specifies on which events the hook will be called: 5802 it is formed by a bitwise OR of the constants 5803 <a name="pdf-LUA_MASKCALL"><code>LUA_MASKCALL</code></a>, 5804 <a name="pdf-LUA_MASKRET"><code>LUA_MASKRET</code></a>, 5805 <a name="pdf-LUA_MASKLINE"><code>LUA_MASKLINE</code></a>, 5806 and <a name="pdf-LUA_MASKCOUNT"><code>LUA_MASKCOUNT</code></a>. 5807 The <code>count</code> argument is only meaningful when the mask 5808 includes <code>LUA_MASKCOUNT</code>. 5809 For each event, the hook is called as explained below: 5810 5811 <ul> 5812 5813 <li><b>The call hook: </b> is called when the interpreter calls a function. 5814 The hook is called just after Lua enters the new function, 5815 before the function gets its arguments. 5816 </li> 5817 5818 <li><b>The return hook: </b> is called when the interpreter returns from a function. 5819 The hook is called just before Lua leaves the function. 5820 There is no standard way to access the values 5821 to be returned by the function. 5822 </li> 5823 5824 <li><b>The line hook: </b> is called when the interpreter is about to 5825 start the execution of a new line of code, 5826 or when it jumps back in the code (even to the same line). 5827 (This event only happens while Lua is executing a Lua function.) 5828 </li> 5829 5830 <li><b>The count hook: </b> is called after the interpreter executes every 5831 <code>count</code> instructions. 5832 (This event only happens while Lua is executing a Lua function.) 5833 </li> 5834 5835 </ul> 5836 5837 <p> 5838 A hook is disabled by setting <code>mask</code> to zero. 5839 5840 5841 5842 5843 5844 <hr><h3><a name="lua_setlocal"><code>lua_setlocal</code></a></h3><p> 5845 <span class="apii">[-(0|1), +0, –]</span> 5846 <pre>const char *lua_setlocal (lua_State *L, const lua_Debug *ar, int n);</pre> 5847 5848 <p> 5849 Sets the value of a local variable of a given activation record. 5850 It assigns the value at the top of the stack 5851 to the variable and returns its name. 5852 It also pops the value from the stack. 5853 5854 5855 <p> 5856 Returns <code>NULL</code> (and pops nothing) 5857 when the index is greater than 5858 the number of active local variables. 5859 5860 5861 <p> 5862 Parameters <code>ar</code> and <code>n</code> are as in function <a href="#lua_getlocal"><code>lua_getlocal</code></a>. 5863 5864 5865 5866 5867 5868 <hr><h3><a name="lua_setupvalue"><code>lua_setupvalue</code></a></h3><p> 5869 <span class="apii">[-(0|1), +0, –]</span> 5870 <pre>const char *lua_setupvalue (lua_State *L, int funcindex, int n);</pre> 5871 5872 <p> 5873 Sets the value of a closure's upvalue. 5874 It assigns the value at the top of the stack 5875 to the upvalue and returns its name. 5876 It also pops the value from the stack. 5877 5878 5879 <p> 5880 Returns <code>NULL</code> (and pops nothing) 5881 when the index <code>n</code> is greater than the number of upvalues. 5882 5883 5884 <p> 5885 Parameters <code>funcindex</code> and <code>n</code> are as in function <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>. 5886 5887 5888 5889 5890 5891 <hr><h3><a name="lua_upvalueid"><code>lua_upvalueid</code></a></h3><p> 5892 <span class="apii">[-0, +0, –]</span> 5893 <pre>void *lua_upvalueid (lua_State *L, int funcindex, int n);</pre> 5894 5895 <p> 5896 Returns a unique identifier for the upvalue numbered <code>n</code> 5897 from the closure at index <code>funcindex</code>. 5898 5899 5900 <p> 5901 These unique identifiers allow a program to check whether different 5902 closures share upvalues. 5903 Lua closures that share an upvalue 5904 (that is, that access a same external local variable) 5905 will return identical ids for those upvalue indices. 5906 5907 5908 <p> 5909 Parameters <code>funcindex</code> and <code>n</code> are as in function <a href="#lua_getupvalue"><code>lua_getupvalue</code></a>, 5910 but <code>n</code> cannot be greater than the number of upvalues. 5911 5912 5913 5914 5915 5916 <hr><h3><a name="lua_upvaluejoin"><code>lua_upvaluejoin</code></a></h3><p> 5917 <span class="apii">[-0, +0, –]</span> 5918 <pre>void lua_upvaluejoin (lua_State *L, int funcindex1, int n1, 5919 int funcindex2, int n2);</pre> 5920 5921 <p> 5922 Make the <code>n1</code>-th upvalue of the Lua closure at index <code>funcindex1</code> 5923 refer to the <code>n2</code>-th upvalue of the Lua closure at index <code>funcindex2</code>. 5924 5925 5926 5927 5928 5929 5930 5931 <h1>5 – <a name="5">The Auxiliary Library</a></h1> 5932 5933 <p> 5934 5935 The <em>auxiliary library</em> provides several convenient functions 5936 to interface C with Lua. 5937 While the basic API provides the primitive functions for all 5938 interactions between C and Lua, 5939 the auxiliary library provides higher-level functions for some 5940 common tasks. 5941 5942 5943 <p> 5944 All functions and types from the auxiliary library 5945 are defined in header file <code>lauxlib.h</code> and 5946 have a prefix <code>luaL_</code>. 5947 5948 5949 <p> 5950 All functions in the auxiliary library are built on 5951 top of the basic API, 5952 and so they provide nothing that cannot be done with that API. 5953 Nevertheless, the use of the auxiliary library ensures 5954 more consistency to your code. 5955 5956 5957 <p> 5958 Several functions in the auxiliary library use internally some 5959 extra stack slots. 5960 When a function in the auxiliary library uses less than five slots, 5961 it does not check the stack size; 5962 it simply assumes that there are enough slots. 5963 5964 5965 <p> 5966 Several functions in the auxiliary library are used to 5967 check C function arguments. 5968 Because the error message is formatted for arguments 5969 (e.g., "<code>bad argument #1</code>"), 5970 you should not use these functions for other stack values. 5971 5972 5973 <p> 5974 Functions called <code>luaL_check*</code> 5975 always raise an error if the check is not satisfied. 5976 5977 5978 5979 <h2>5.1 – <a name="5.1">Functions and Types</a></h2> 5980 5981 <p> 5982 Here we list all functions and types from the auxiliary library 5983 in alphabetical order. 5984 5985 5986 5987 <hr><h3><a name="luaL_addchar"><code>luaL_addchar</code></a></h3><p> 5988 <span class="apii">[-?, +?, <em>m</em>]</span> 5989 <pre>void luaL_addchar (luaL_Buffer *B, char c);</pre> 5990 5991 <p> 5992 Adds the byte <code>c</code> to the buffer <code>B</code> 5993 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). 5994 5995 5996 5997 5998 5999 <hr><h3><a name="luaL_addlstring"><code>luaL_addlstring</code></a></h3><p> 6000 <span class="apii">[-?, +?, <em>m</em>]</span> 6001 <pre>void luaL_addlstring (luaL_Buffer *B, const char *s, size_t l);</pre> 6002 6003 <p> 6004 Adds the string pointed to by <code>s</code> with length <code>l</code> to 6005 the buffer <code>B</code> 6006 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). 6007 The string can contain embedded zeros. 6008 6009 6010 6011 6012 6013 <hr><h3><a name="luaL_addsize"><code>luaL_addsize</code></a></h3><p> 6014 <span class="apii">[-?, +?, –]</span> 6015 <pre>void luaL_addsize (luaL_Buffer *B, size_t n);</pre> 6016 6017 <p> 6018 Adds to the buffer <code>B</code> (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>) 6019 a string of length <code>n</code> previously copied to the 6020 buffer area (see <a href="#luaL_prepbuffer"><code>luaL_prepbuffer</code></a>). 6021 6022 6023 6024 6025 6026 <hr><h3><a name="luaL_addstring"><code>luaL_addstring</code></a></h3><p> 6027 <span class="apii">[-?, +?, <em>m</em>]</span> 6028 <pre>void luaL_addstring (luaL_Buffer *B, const char *s);</pre> 6029 6030 <p> 6031 Adds the zero-terminated string pointed to by <code>s</code> 6032 to the buffer <code>B</code> 6033 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). 6034 6035 6036 6037 6038 6039 <hr><h3><a name="luaL_addvalue"><code>luaL_addvalue</code></a></h3><p> 6040 <span class="apii">[-1, +?, <em>m</em>]</span> 6041 <pre>void luaL_addvalue (luaL_Buffer *B);</pre> 6042 6043 <p> 6044 Adds the value at the top of the stack 6045 to the buffer <code>B</code> 6046 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). 6047 Pops the value. 6048 6049 6050 <p> 6051 This is the only function on string buffers that can (and must) 6052 be called with an extra element on the stack, 6053 which is the value to be added to the buffer. 6054 6055 6056 6057 6058 6059 <hr><h3><a name="luaL_argcheck"><code>luaL_argcheck</code></a></h3><p> 6060 <span class="apii">[-0, +0, <em>v</em>]</span> 6061 <pre>void luaL_argcheck (lua_State *L, 6062 int cond, 6063 int arg, 6064 const char *extramsg);</pre> 6065 6066 <p> 6067 Checks whether <code>cond</code> is true. 6068 If it is not, raises an error with a standard message (see <a href="#luaL_argerror"><code>luaL_argerror</code></a>). 6069 6070 6071 6072 6073 6074 <hr><h3><a name="luaL_argerror"><code>luaL_argerror</code></a></h3><p> 6075 <span class="apii">[-0, +0, <em>v</em>]</span> 6076 <pre>int luaL_argerror (lua_State *L, int arg, const char *extramsg);</pre> 6077 6078 <p> 6079 Raises an error reporting a problem with argument <code>arg</code> 6080 of the C function that called it, 6081 using a standard message 6082 that includes <code>extramsg</code> as a comment: 6083 6084 <pre> 6085 bad argument #<em>arg</em> to '<em>funcname</em>' (<em>extramsg</em>) 6086 </pre><p> 6087 This function never returns. 6088 6089 6090 6091 6092 6093 <hr><h3><a name="luaL_Buffer"><code>luaL_Buffer</code></a></h3> 6094 <pre>typedef struct luaL_Buffer luaL_Buffer;</pre> 6095 6096 <p> 6097 Type for a <em>string buffer</em>. 6098 6099 6100 <p> 6101 A string buffer allows C code to build Lua strings piecemeal. 6102 Its pattern of use is as follows: 6103 6104 <ul> 6105 6106 <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> 6107 6108 <li>Then initialize it with a call <code>luaL_buffinit(L, &b)</code>.</li> 6109 6110 <li> 6111 Then add string pieces to the buffer calling any of 6112 the <code>luaL_add*</code> functions. 6113 </li> 6114 6115 <li> 6116 Finish by calling <code>luaL_pushresult(&b)</code>. 6117 This call leaves the final string on the top of the stack. 6118 </li> 6119 6120 </ul> 6121 6122 <p> 6123 If you know beforehand the total size of the resulting string, 6124 you can use the buffer like this: 6125 6126 <ul> 6127 6128 <li>First declare a variable <code>b</code> of type <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>.</li> 6129 6130 <li>Then initialize it and preallocate a space of 6131 size <code>sz</code> with a call <code>luaL_buffinitsize(L, &b, sz)</code>.</li> 6132 6133 <li>Then copy the string into that space.</li> 6134 6135 <li> 6136 Finish by calling <code>luaL_pushresultsize(&b, sz)</code>, 6137 where <code>sz</code> is the total size of the resulting string 6138 copied into that space. 6139 </li> 6140 6141 </ul> 6142 6143 <p> 6144 During its normal operation, 6145 a string buffer uses a variable number of stack slots. 6146 So, while using a buffer, you cannot assume that you know where 6147 the top of the stack is. 6148 You can use the stack between successive calls to buffer operations 6149 as long as that use is balanced; 6150 that is, 6151 when you call a buffer operation, 6152 the stack is at the same level 6153 it was immediately after the previous buffer operation. 6154 (The only exception to this rule is <a href="#luaL_addvalue"><code>luaL_addvalue</code></a>.) 6155 After calling <a href="#luaL_pushresult"><code>luaL_pushresult</code></a> the stack is back to its 6156 level when the buffer was initialized, 6157 plus the final string on its top. 6158 6159 6160 6161 6162 6163 <hr><h3><a name="luaL_buffinit"><code>luaL_buffinit</code></a></h3><p> 6164 <span class="apii">[-0, +0, –]</span> 6165 <pre>void luaL_buffinit (lua_State *L, luaL_Buffer *B);</pre> 6166 6167 <p> 6168 Initializes a buffer <code>B</code>. 6169 This function does not allocate any space; 6170 the buffer must be declared as a variable 6171 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). 6172 6173 6174 6175 6176 6177 <hr><h3><a name="luaL_buffinitsize"><code>luaL_buffinitsize</code></a></h3><p> 6178 <span class="apii">[-?, +?, <em>m</em>]</span> 6179 <pre>char *luaL_buffinitsize (lua_State *L, luaL_Buffer *B, size_t sz);</pre> 6180 6181 <p> 6182 Equivalent to the sequence 6183 <a href="#luaL_buffinit"><code>luaL_buffinit</code></a>, <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a>. 6184 6185 6186 6187 6188 6189 <hr><h3><a name="luaL_callmeta"><code>luaL_callmeta</code></a></h3><p> 6190 <span class="apii">[-0, +(0|1), <em>e</em>]</span> 6191 <pre>int luaL_callmeta (lua_State *L, int obj, const char *e);</pre> 6192 6193 <p> 6194 Calls a metamethod. 6195 6196 6197 <p> 6198 If the object at index <code>obj</code> has a metatable and this 6199 metatable has a field <code>e</code>, 6200 this function calls this field passing the object as its only argument. 6201 In this case this function returns true and pushes onto the 6202 stack the value returned by the call. 6203 If there is no metatable or no metamethod, 6204 this function returns false (without pushing any value on the stack). 6205 6206 6207 6208 6209 6210 <hr><h3><a name="luaL_checkany"><code>luaL_checkany</code></a></h3><p> 6211 <span class="apii">[-0, +0, <em>v</em>]</span> 6212 <pre>void luaL_checkany (lua_State *L, int arg);</pre> 6213 6214 <p> 6215 Checks whether the function has an argument 6216 of any type (including <b>nil</b>) at position <code>arg</code>. 6217 6218 6219 6220 6221 6222 <hr><h3><a name="luaL_checkinteger"><code>luaL_checkinteger</code></a></h3><p> 6223 <span class="apii">[-0, +0, <em>v</em>]</span> 6224 <pre>lua_Integer luaL_checkinteger (lua_State *L, int arg);</pre> 6225 6226 <p> 6227 Checks whether the function argument <code>arg</code> is an integer 6228 (or can be converted to an integer) 6229 and returns this integer cast to a <a href="#lua_Integer"><code>lua_Integer</code></a>. 6230 6231 6232 6233 6234 6235 <hr><h3><a name="luaL_checklstring"><code>luaL_checklstring</code></a></h3><p> 6236 <span class="apii">[-0, +0, <em>v</em>]</span> 6237 <pre>const char *luaL_checklstring (lua_State *L, int arg, size_t *l);</pre> 6238 6239 <p> 6240 Checks whether the function argument <code>arg</code> is a string 6241 and returns this string; 6242 if <code>l</code> is not <code>NULL</code> fills <code>*l</code> 6243 with the string's length. 6244 6245 6246 <p> 6247 This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, 6248 so all conversions and caveats of that function apply here. 6249 6250 6251 6252 6253 6254 <hr><h3><a name="luaL_checknumber"><code>luaL_checknumber</code></a></h3><p> 6255 <span class="apii">[-0, +0, <em>v</em>]</span> 6256 <pre>lua_Number luaL_checknumber (lua_State *L, int arg);</pre> 6257 6258 <p> 6259 Checks whether the function argument <code>arg</code> is a number 6260 and returns this number. 6261 6262 6263 6264 6265 6266 <hr><h3><a name="luaL_checkoption"><code>luaL_checkoption</code></a></h3><p> 6267 <span class="apii">[-0, +0, <em>v</em>]</span> 6268 <pre>int luaL_checkoption (lua_State *L, 6269 int arg, 6270 const char *def, 6271 const char *const lst[]);</pre> 6272 6273 <p> 6274 Checks whether the function argument <code>arg</code> is a string and 6275 searches for this string in the array <code>lst</code> 6276 (which must be NULL-terminated). 6277 Returns the index in the array where the string was found. 6278 Raises an error if the argument is not a string or 6279 if the string cannot be found. 6280 6281 6282 <p> 6283 If <code>def</code> is not <code>NULL</code>, 6284 the function uses <code>def</code> as a default value when 6285 there is no argument <code>arg</code> or when this argument is <b>nil</b>. 6286 6287 6288 <p> 6289 This is a useful function for mapping strings to C enums. 6290 (The usual convention in Lua libraries is 6291 to use strings instead of numbers to select options.) 6292 6293 6294 6295 6296 6297 <hr><h3><a name="luaL_checkstack"><code>luaL_checkstack</code></a></h3><p> 6298 <span class="apii">[-0, +0, <em>v</em>]</span> 6299 <pre>void luaL_checkstack (lua_State *L, int sz, const char *msg);</pre> 6300 6301 <p> 6302 Grows the stack size to <code>top + sz</code> elements, 6303 raising an error if the stack cannot grow to that size. 6304 <code>msg</code> is an additional text to go into the error message 6305 (or <code>NULL</code> for no additional text). 6306 6307 6308 6309 6310 6311 <hr><h3><a name="luaL_checkstring"><code>luaL_checkstring</code></a></h3><p> 6312 <span class="apii">[-0, +0, <em>v</em>]</span> 6313 <pre>const char *luaL_checkstring (lua_State *L, int arg);</pre> 6314 6315 <p> 6316 Checks whether the function argument <code>arg</code> is a string 6317 and returns this string. 6318 6319 6320 <p> 6321 This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, 6322 so all conversions and caveats of that function apply here. 6323 6324 6325 6326 6327 6328 <hr><h3><a name="luaL_checktype"><code>luaL_checktype</code></a></h3><p> 6329 <span class="apii">[-0, +0, <em>v</em>]</span> 6330 <pre>void luaL_checktype (lua_State *L, int arg, int t);</pre> 6331 6332 <p> 6333 Checks whether the function argument <code>arg</code> has type <code>t</code>. 6334 See <a href="#lua_type"><code>lua_type</code></a> for the encoding of types for <code>t</code>. 6335 6336 6337 6338 6339 6340 <hr><h3><a name="luaL_checkudata"><code>luaL_checkudata</code></a></h3><p> 6341 <span class="apii">[-0, +0, <em>v</em>]</span> 6342 <pre>void *luaL_checkudata (lua_State *L, int arg, const char *tname);</pre> 6343 6344 <p> 6345 Checks whether the function argument <code>arg</code> is a userdata 6346 of the type <code>tname</code> (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) and 6347 returns the userdata address (see <a href="#lua_touserdata"><code>lua_touserdata</code></a>). 6348 6349 6350 6351 6352 6353 <hr><h3><a name="luaL_checkversion"><code>luaL_checkversion</code></a></h3><p> 6354 <span class="apii">[-0, +0, <em>v</em>]</span> 6355 <pre>void luaL_checkversion (lua_State *L);</pre> 6356 6357 <p> 6358 Checks whether the core running the call, 6359 the core that created the Lua state, 6360 and the code making the call are all using the same version of Lua. 6361 Also checks whether the core running the call 6362 and the core that created the Lua state 6363 are using the same address space. 6364 6365 6366 6367 6368 6369 <hr><h3><a name="luaL_dofile"><code>luaL_dofile</code></a></h3><p> 6370 <span class="apii">[-0, +?, <em>e</em>]</span> 6371 <pre>int luaL_dofile (lua_State *L, const char *filename);</pre> 6372 6373 <p> 6374 Loads and runs the given file. 6375 It is defined as the following macro: 6376 6377 <pre> 6378 (luaL_loadfile(L, filename) || lua_pcall(L, 0, LUA_MULTRET, 0)) 6379 </pre><p> 6380 It returns false if there are no errors 6381 or true in case of errors. 6382 6383 6384 6385 6386 6387 <hr><h3><a name="luaL_dostring"><code>luaL_dostring</code></a></h3><p> 6388 <span class="apii">[-0, +?, –]</span> 6389 <pre>int luaL_dostring (lua_State *L, const char *str);</pre> 6390 6391 <p> 6392 Loads and runs the given string. 6393 It is defined as the following macro: 6394 6395 <pre> 6396 (luaL_loadstring(L, str) || lua_pcall(L, 0, LUA_MULTRET, 0)) 6397 </pre><p> 6398 It returns false if there are no errors 6399 or true in case of errors. 6400 6401 6402 6403 6404 6405 <hr><h3><a name="luaL_error"><code>luaL_error</code></a></h3><p> 6406 <span class="apii">[-0, +0, <em>v</em>]</span> 6407 <pre>int luaL_error (lua_State *L, const char *fmt, ...);</pre> 6408 6409 <p> 6410 Raises an error. 6411 The error message format is given by <code>fmt</code> 6412 plus any extra arguments, 6413 following the same rules of <a href="#lua_pushfstring"><code>lua_pushfstring</code></a>. 6414 It also adds at the beginning of the message the file name and 6415 the line number where the error occurred, 6416 if this information is available. 6417 6418 6419 <p> 6420 This function never returns, 6421 but it is an idiom to use it in C functions 6422 as <code>return luaL_error(<em>args</em>)</code>. 6423 6424 6425 6426 6427 6428 <hr><h3><a name="luaL_execresult"><code>luaL_execresult</code></a></h3><p> 6429 <span class="apii">[-0, +3, <em>m</em>]</span> 6430 <pre>int luaL_execresult (lua_State *L, int stat);</pre> 6431 6432 <p> 6433 This function produces the return values for 6434 process-related functions in the standard library 6435 (<a href="#pdf-os.execute"><code>os.execute</code></a> and <a href="#pdf-io.close"><code>io.close</code></a>). 6436 6437 6438 6439 6440 6441 <hr><h3><a name="luaL_fileresult"><code>luaL_fileresult</code></a></h3><p> 6442 <span class="apii">[-0, +(1|3), <em>m</em>]</span> 6443 <pre>int luaL_fileresult (lua_State *L, int stat, const char *fname);</pre> 6444 6445 <p> 6446 This function produces the return values for 6447 file-related functions in the standard library 6448 (<a href="#pdf-io.open"><code>io.open</code></a>, <a href="#pdf-os.rename"><code>os.rename</code></a>, <a href="#pdf-file:seek"><code>file:seek</code></a>, etc.). 6449 6450 6451 6452 6453 6454 <hr><h3><a name="luaL_getmetafield"><code>luaL_getmetafield</code></a></h3><p> 6455 <span class="apii">[-0, +(0|1), <em>m</em>]</span> 6456 <pre>int luaL_getmetafield (lua_State *L, int obj, const char *e);</pre> 6457 6458 <p> 6459 Pushes onto the stack the field <code>e</code> from the metatable 6460 of the object at index <code>obj</code> and returns the type of the pushed value. 6461 If the object does not have a metatable, 6462 or if the metatable does not have this field, 6463 pushes nothing and returns <code>LUA_TNIL</code>. 6464 6465 6466 6467 6468 6469 <hr><h3><a name="luaL_getmetatable"><code>luaL_getmetatable</code></a></h3><p> 6470 <span class="apii">[-0, +1, <em>m</em>]</span> 6471 <pre>int luaL_getmetatable (lua_State *L, const char *tname);</pre> 6472 6473 <p> 6474 Pushes onto the stack the metatable associated with name <code>tname</code> 6475 in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>) 6476 (<b>nil</b> if there is no metatable associated with that name). 6477 Returns the type of the pushed value. 6478 6479 6480 6481 6482 6483 <hr><h3><a name="luaL_getsubtable"><code>luaL_getsubtable</code></a></h3><p> 6484 <span class="apii">[-0, +1, <em>e</em>]</span> 6485 <pre>int luaL_getsubtable (lua_State *L, int idx, const char *fname);</pre> 6486 6487 <p> 6488 Ensures that the value <code>t[fname]</code>, 6489 where <code>t</code> is the value at index <code>idx</code>, 6490 is a table, 6491 and pushes that table onto the stack. 6492 Returns true if it finds a previous table there 6493 and false if it creates a new table. 6494 6495 6496 6497 6498 6499 <hr><h3><a name="luaL_gsub"><code>luaL_gsub</code></a></h3><p> 6500 <span class="apii">[-0, +1, <em>m</em>]</span> 6501 <pre>const char *luaL_gsub (lua_State *L, 6502 const char *s, 6503 const char *p, 6504 const char *r);</pre> 6505 6506 <p> 6507 Creates a copy of string <code>s</code> by replacing 6508 any occurrence of the string <code>p</code> 6509 with the string <code>r</code>. 6510 Pushes the resulting string on the stack and returns it. 6511 6512 6513 6514 6515 6516 <hr><h3><a name="luaL_len"><code>luaL_len</code></a></h3><p> 6517 <span class="apii">[-0, +0, <em>e</em>]</span> 6518 <pre>lua_Integer luaL_len (lua_State *L, int index);</pre> 6519 6520 <p> 6521 Returns the "length" of the value at the given index 6522 as a number; 6523 it is equivalent to the '<code>#</code>' operator in Lua (see <a href="#3.4.7">§3.4.7</a>). 6524 Raises an error if the result of the operation is not an integer. 6525 (This case only can happen through metamethods.) 6526 6527 6528 6529 6530 6531 <hr><h3><a name="luaL_loadbuffer"><code>luaL_loadbuffer</code></a></h3><p> 6532 <span class="apii">[-0, +1, –]</span> 6533 <pre>int luaL_loadbuffer (lua_State *L, 6534 const char *buff, 6535 size_t sz, 6536 const char *name);</pre> 6537 6538 <p> 6539 Equivalent to <a href="#luaL_loadbufferx"><code>luaL_loadbufferx</code></a> with <code>mode</code> equal to <code>NULL</code>. 6540 6541 6542 6543 6544 6545 <hr><h3><a name="luaL_loadbufferx"><code>luaL_loadbufferx</code></a></h3><p> 6546 <span class="apii">[-0, +1, –]</span> 6547 <pre>int luaL_loadbufferx (lua_State *L, 6548 const char *buff, 6549 size_t sz, 6550 const char *name, 6551 const char *mode);</pre> 6552 6553 <p> 6554 Loads a buffer as a Lua chunk. 6555 This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the 6556 buffer pointed to by <code>buff</code> with size <code>sz</code>. 6557 6558 6559 <p> 6560 This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. 6561 <code>name</code> is the chunk name, 6562 used for debug information and error messages. 6563 The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>. 6564 6565 6566 6567 6568 6569 <hr><h3><a name="luaL_loadfile"><code>luaL_loadfile</code></a></h3><p> 6570 <span class="apii">[-0, +1, <em>m</em>]</span> 6571 <pre>int luaL_loadfile (lua_State *L, const char *filename);</pre> 6572 6573 <p> 6574 Equivalent to <a href="#luaL_loadfilex"><code>luaL_loadfilex</code></a> with <code>mode</code> equal to <code>NULL</code>. 6575 6576 6577 6578 6579 6580 <hr><h3><a name="luaL_loadfilex"><code>luaL_loadfilex</code></a></h3><p> 6581 <span class="apii">[-0, +1, <em>m</em>]</span> 6582 <pre>int luaL_loadfilex (lua_State *L, const char *filename, 6583 const char *mode);</pre> 6584 6585 <p> 6586 Loads a file as a Lua chunk. 6587 This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in the file 6588 named <code>filename</code>. 6589 If <code>filename</code> is <code>NULL</code>, 6590 then it loads from the standard input. 6591 The first line in the file is ignored if it starts with a <code>#</code>. 6592 6593 6594 <p> 6595 The string <code>mode</code> works as in function <a href="#lua_load"><code>lua_load</code></a>. 6596 6597 6598 <p> 6599 This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>, 6600 but it has an extra error code <a name="pdf-LUA_ERRFILE"><code>LUA_ERRFILE</code></a> 6601 for file-related errors 6602 (e.g., it cannot open or read the file). 6603 6604 6605 <p> 6606 As <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; 6607 it does not run it. 6608 6609 6610 6611 6612 6613 <hr><h3><a name="luaL_loadstring"><code>luaL_loadstring</code></a></h3><p> 6614 <span class="apii">[-0, +1, –]</span> 6615 <pre>int luaL_loadstring (lua_State *L, const char *s);</pre> 6616 6617 <p> 6618 Loads a string as a Lua chunk. 6619 This function uses <a href="#lua_load"><code>lua_load</code></a> to load the chunk in 6620 the zero-terminated string <code>s</code>. 6621 6622 6623 <p> 6624 This function returns the same results as <a href="#lua_load"><code>lua_load</code></a>. 6625 6626 6627 <p> 6628 Also as <a href="#lua_load"><code>lua_load</code></a>, this function only loads the chunk; 6629 it does not run it. 6630 6631 6632 6633 6634 6635 <hr><h3><a name="luaL_newlib"><code>luaL_newlib</code></a></h3><p> 6636 <span class="apii">[-0, +1, <em>m</em>]</span> 6637 <pre>void luaL_newlib (lua_State *L, const luaL_Reg l[]);</pre> 6638 6639 <p> 6640 Creates a new table and registers there 6641 the functions in list <code>l</code>. 6642 6643 6644 <p> 6645 It is implemented as the following macro: 6646 6647 <pre> 6648 (luaL_newlibtable(L,l), luaL_setfuncs(L,l,0)) 6649 </pre><p> 6650 The array <code>l</code> must be the actual array, 6651 not a pointer to it. 6652 6653 6654 6655 6656 6657 <hr><h3><a name="luaL_newlibtable"><code>luaL_newlibtable</code></a></h3><p> 6658 <span class="apii">[-0, +1, <em>m</em>]</span> 6659 <pre>void luaL_newlibtable (lua_State *L, const luaL_Reg l[]);</pre> 6660 6661 <p> 6662 Creates a new table with a size optimized 6663 to store all entries in the array <code>l</code> 6664 (but does not actually store them). 6665 It is intended to be used in conjunction with <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a> 6666 (see <a href="#luaL_newlib"><code>luaL_newlib</code></a>). 6667 6668 6669 <p> 6670 It is implemented as a macro. 6671 The array <code>l</code> must be the actual array, 6672 not a pointer to it. 6673 6674 6675 6676 6677 6678 <hr><h3><a name="luaL_newmetatable"><code>luaL_newmetatable</code></a></h3><p> 6679 <span class="apii">[-0, +1, <em>m</em>]</span> 6680 <pre>int luaL_newmetatable (lua_State *L, const char *tname);</pre> 6681 6682 <p> 6683 If the registry already has the key <code>tname</code>, 6684 returns 0. 6685 Otherwise, 6686 creates a new table to be used as a metatable for userdata, 6687 adds to this new table the pair <code>__name = tname</code>, 6688 adds to the registry the pair <code>[tname] = new table</code>, 6689 and returns 1. 6690 (The entry <code>__name</code> is used by some error-reporting functions.) 6691 6692 6693 <p> 6694 In both cases pushes onto the stack the final value associated 6695 with <code>tname</code> in the registry. 6696 6697 6698 6699 6700 6701 <hr><h3><a name="luaL_newstate"><code>luaL_newstate</code></a></h3><p> 6702 <span class="apii">[-0, +0, –]</span> 6703 <pre>lua_State *luaL_newstate (void);</pre> 6704 6705 <p> 6706 Creates a new Lua state. 6707 It calls <a href="#lua_newstate"><code>lua_newstate</code></a> with an 6708 allocator based on the standard C <code>realloc</code> function 6709 and then sets a panic function (see <a href="#4.6">§4.6</a>) that prints 6710 an error message to the standard error output in case of fatal 6711 errors. 6712 6713 6714 <p> 6715 Returns the new state, 6716 or <code>NULL</code> if there is a memory allocation error. 6717 6718 6719 6720 6721 6722 <hr><h3><a name="luaL_openlibs"><code>luaL_openlibs</code></a></h3><p> 6723 <span class="apii">[-0, +0, <em>e</em>]</span> 6724 <pre>void luaL_openlibs (lua_State *L);</pre> 6725 6726 <p> 6727 Opens all standard Lua libraries into the given state. 6728 6729 6730 6731 6732 6733 <hr><h3><a name="luaL_opt"><code>luaL_opt</code></a></h3><p> 6734 <span class="apii">[-0, +0, <em>e</em>]</span> 6735 <pre>T luaL_opt (L, func, arg, dflt);</pre> 6736 6737 <p> 6738 This macro is defined as follows: 6739 6740 <pre> 6741 (lua_isnoneornil(L,(arg)) ? (dflt) : func(L,(arg))) 6742 </pre><p> 6743 In words, if the argument <code>arg</code> is nil or absent, 6744 the macro results in the default <code>dflt</code>. 6745 Otherwise, it results in the result of calling <code>func</code> 6746 with the state <code>L</code> and the argument index <code>arg</code> as 6747 arguments. 6748 Note that it evaluates the expression <code>dflt</code> only if needed. 6749 6750 6751 6752 6753 6754 <hr><h3><a name="luaL_optinteger"><code>luaL_optinteger</code></a></h3><p> 6755 <span class="apii">[-0, +0, <em>v</em>]</span> 6756 <pre>lua_Integer luaL_optinteger (lua_State *L, 6757 int arg, 6758 lua_Integer d);</pre> 6759 6760 <p> 6761 If the function argument <code>arg</code> is an integer 6762 (or convertible to an integer), 6763 returns this integer. 6764 If this argument is absent or is <b>nil</b>, 6765 returns <code>d</code>. 6766 Otherwise, raises an error. 6767 6768 6769 6770 6771 6772 <hr><h3><a name="luaL_optlstring"><code>luaL_optlstring</code></a></h3><p> 6773 <span class="apii">[-0, +0, <em>v</em>]</span> 6774 <pre>const char *luaL_optlstring (lua_State *L, 6775 int arg, 6776 const char *d, 6777 size_t *l);</pre> 6778 6779 <p> 6780 If the function argument <code>arg</code> is a string, 6781 returns this string. 6782 If this argument is absent or is <b>nil</b>, 6783 returns <code>d</code>. 6784 Otherwise, raises an error. 6785 6786 6787 <p> 6788 If <code>l</code> is not <code>NULL</code>, 6789 fills the position <code>*l</code> with the result's length. 6790 If the result is <code>NULL</code> 6791 (only possible when returning <code>d</code> and <code>d == NULL</code>), 6792 its length is considered zero. 6793 6794 6795 <p> 6796 This function uses <a href="#lua_tolstring"><code>lua_tolstring</code></a> to get its result, 6797 so all conversions and caveats of that function apply here. 6798 6799 6800 6801 6802 6803 <hr><h3><a name="luaL_optnumber"><code>luaL_optnumber</code></a></h3><p> 6804 <span class="apii">[-0, +0, <em>v</em>]</span> 6805 <pre>lua_Number luaL_optnumber (lua_State *L, int arg, lua_Number d);</pre> 6806 6807 <p> 6808 If the function argument <code>arg</code> is a number, 6809 returns this number. 6810 If this argument is absent or is <b>nil</b>, 6811 returns <code>d</code>. 6812 Otherwise, raises an error. 6813 6814 6815 6816 6817 6818 <hr><h3><a name="luaL_optstring"><code>luaL_optstring</code></a></h3><p> 6819 <span class="apii">[-0, +0, <em>v</em>]</span> 6820 <pre>const char *luaL_optstring (lua_State *L, 6821 int arg, 6822 const char *d);</pre> 6823 6824 <p> 6825 If the function argument <code>arg</code> is a string, 6826 returns this string. 6827 If this argument is absent or is <b>nil</b>, 6828 returns <code>d</code>. 6829 Otherwise, raises an error. 6830 6831 6832 6833 6834 6835 <hr><h3><a name="luaL_prepbuffer"><code>luaL_prepbuffer</code></a></h3><p> 6836 <span class="apii">[-?, +?, <em>m</em>]</span> 6837 <pre>char *luaL_prepbuffer (luaL_Buffer *B);</pre> 6838 6839 <p> 6840 Equivalent to <a href="#luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a> 6841 with the predefined size <a name="pdf-LUAL_BUFFERSIZE"><code>LUAL_BUFFERSIZE</code></a>. 6842 6843 6844 6845 6846 6847 <hr><h3><a name="luaL_prepbuffsize"><code>luaL_prepbuffsize</code></a></h3><p> 6848 <span class="apii">[-?, +?, <em>m</em>]</span> 6849 <pre>char *luaL_prepbuffsize (luaL_Buffer *B, size_t sz);</pre> 6850 6851 <p> 6852 Returns an address to a space of size <code>sz</code> 6853 where you can copy a string to be added to buffer <code>B</code> 6854 (see <a href="#luaL_Buffer"><code>luaL_Buffer</code></a>). 6855 After copying the string into this space you must call 6856 <a href="#luaL_addsize"><code>luaL_addsize</code></a> with the size of the string to actually add 6857 it to the buffer. 6858 6859 6860 6861 6862 6863 <hr><h3><a name="luaL_pushresult"><code>luaL_pushresult</code></a></h3><p> 6864 <span class="apii">[-?, +1, <em>m</em>]</span> 6865 <pre>void luaL_pushresult (luaL_Buffer *B);</pre> 6866 6867 <p> 6868 Finishes the use of buffer <code>B</code> leaving the final string on 6869 the top of the stack. 6870 6871 6872 6873 6874 6875 <hr><h3><a name="luaL_pushresultsize"><code>luaL_pushresultsize</code></a></h3><p> 6876 <span class="apii">[-?, +1, <em>m</em>]</span> 6877 <pre>void luaL_pushresultsize (luaL_Buffer *B, size_t sz);</pre> 6878 6879 <p> 6880 Equivalent to the sequence <a href="#luaL_addsize"><code>luaL_addsize</code></a>, <a href="#luaL_pushresult"><code>luaL_pushresult</code></a>. 6881 6882 6883 6884 6885 6886 <hr><h3><a name="luaL_ref"><code>luaL_ref</code></a></h3><p> 6887 <span class="apii">[-1, +0, <em>m</em>]</span> 6888 <pre>int luaL_ref (lua_State *L, int t);</pre> 6889 6890 <p> 6891 Creates and returns a <em>reference</em>, 6892 in the table at index <code>t</code>, 6893 for the object at the top of the stack (and pops the object). 6894 6895 6896 <p> 6897 A reference is a unique integer key. 6898 As long as you do not manually add integer keys into table <code>t</code>, 6899 <a href="#luaL_ref"><code>luaL_ref</code></a> ensures the uniqueness of the key it returns. 6900 You can retrieve an object referred by reference <code>r</code> 6901 by calling <code>lua_rawgeti(L, t, r)</code>. 6902 Function <a href="#luaL_unref"><code>luaL_unref</code></a> frees a reference and its associated object. 6903 6904 6905 <p> 6906 If the object at the top of the stack is <b>nil</b>, 6907 <a href="#luaL_ref"><code>luaL_ref</code></a> returns the constant <a name="pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>. 6908 The constant <a name="pdf-LUA_NOREF"><code>LUA_NOREF</code></a> is guaranteed to be different 6909 from any reference returned by <a href="#luaL_ref"><code>luaL_ref</code></a>. 6910 6911 6912 6913 6914 6915 <hr><h3><a name="luaL_Reg"><code>luaL_Reg</code></a></h3> 6916 <pre>typedef struct luaL_Reg { 6917 const char *name; 6918 lua_CFunction func; 6919 } luaL_Reg;</pre> 6920 6921 <p> 6922 Type for arrays of functions to be registered by 6923 <a href="#luaL_setfuncs"><code>luaL_setfuncs</code></a>. 6924 <code>name</code> is the function name and <code>func</code> is a pointer to 6925 the function. 6926 Any array of <a href="#luaL_Reg"><code>luaL_Reg</code></a> must end with a sentinel entry 6927 in which both <code>name</code> and <code>func</code> are <code>NULL</code>. 6928 6929 6930 6931 6932 6933 <hr><h3><a name="luaL_requiref"><code>luaL_requiref</code></a></h3><p> 6934 <span class="apii">[-0, +1, <em>e</em>]</span> 6935 <pre>void luaL_requiref (lua_State *L, const char *modname, 6936 lua_CFunction openf, int glb);</pre> 6937 6938 <p> 6939 If <code>modname</code> is not already present in <a href="#pdf-package.loaded"><code>package.loaded</code></a>, 6940 calls function <code>openf</code> with string <code>modname</code> as an argument 6941 and sets the call result in <code>package.loaded[modname]</code>, 6942 as if that function has been called through <a href="#pdf-require"><code>require</code></a>. 6943 6944 6945 <p> 6946 If <code>glb</code> is true, 6947 also stores the module into global <code>modname</code>. 6948 6949 6950 <p> 6951 Leaves a copy of the module on the stack. 6952 6953 6954 6955 6956 6957 <hr><h3><a name="luaL_setfuncs"><code>luaL_setfuncs</code></a></h3><p> 6958 <span class="apii">[-nup, +0, <em>m</em>]</span> 6959 <pre>void luaL_setfuncs (lua_State *L, const luaL_Reg *l, int nup);</pre> 6960 6961 <p> 6962 Registers all functions in the array <code>l</code> 6963 (see <a href="#luaL_Reg"><code>luaL_Reg</code></a>) into the table on the top of the stack 6964 (below optional upvalues, see next). 6965 6966 6967 <p> 6968 When <code>nup</code> is not zero, 6969 all functions are created sharing <code>nup</code> upvalues, 6970 which must be previously pushed on the stack 6971 on top of the library table. 6972 These values are popped from the stack after the registration. 6973 6974 6975 6976 6977 6978 <hr><h3><a name="luaL_setmetatable"><code>luaL_setmetatable</code></a></h3><p> 6979 <span class="apii">[-0, +0, –]</span> 6980 <pre>void luaL_setmetatable (lua_State *L, const char *tname);</pre> 6981 6982 <p> 6983 Sets the metatable of the object at the top of the stack 6984 as the metatable associated with name <code>tname</code> 6985 in the registry (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). 6986 6987 6988 6989 6990 6991 <hr><h3><a name="luaL_Stream"><code>luaL_Stream</code></a></h3> 6992 <pre>typedef struct luaL_Stream { 6993 FILE *f; 6994 lua_CFunction closef; 6995 } luaL_Stream;</pre> 6996 6997 <p> 6998 The standard representation for file handles, 6999 which is used by the standard I/O library. 7000 7001 7002 <p> 7003 A file handle is implemented as a full userdata, 7004 with a metatable called <code>LUA_FILEHANDLE</code> 7005 (where <code>LUA_FILEHANDLE</code> is a macro with the actual metatable's name). 7006 The metatable is created by the I/O library 7007 (see <a href="#luaL_newmetatable"><code>luaL_newmetatable</code></a>). 7008 7009 7010 <p> 7011 This userdata must start with the structure <code>luaL_Stream</code>; 7012 it can contain other data after this initial structure. 7013 Field <code>f</code> points to the corresponding C stream 7014 (or it can be <code>NULL</code> to indicate an incompletely created handle). 7015 Field <code>closef</code> points to a Lua function 7016 that will be called to close the stream 7017 when the handle is closed or collected; 7018 this function receives the file handle as its sole argument and 7019 must return either <b>true</b> (in case of success) 7020 or <b>nil</b> plus an error message (in case of error). 7021 Once Lua calls this field, 7022 it changes the field value to <code>NULL</code> 7023 to signal that the handle is closed. 7024 7025 7026 7027 7028 7029 <hr><h3><a name="luaL_testudata"><code>luaL_testudata</code></a></h3><p> 7030 <span class="apii">[-0, +0, <em>m</em>]</span> 7031 <pre>void *luaL_testudata (lua_State *L, int arg, const char *tname);</pre> 7032 7033 <p> 7034 This function works like <a href="#luaL_checkudata"><code>luaL_checkudata</code></a>, 7035 except that, when the test fails, 7036 it returns <code>NULL</code> instead of raising an error. 7037 7038 7039 7040 7041 7042 <hr><h3><a name="luaL_tolstring"><code>luaL_tolstring</code></a></h3><p> 7043 <span class="apii">[-0, +1, <em>e</em>]</span> 7044 <pre>const char *luaL_tolstring (lua_State *L, int idx, size_t *len);</pre> 7045 7046 <p> 7047 Converts any Lua value at the given index to a C string 7048 in a reasonable format. 7049 The resulting string is pushed onto the stack and also 7050 returned by the function. 7051 If <code>len</code> is not <code>NULL</code>, 7052 the function also sets <code>*len</code> with the string length. 7053 7054 7055 <p> 7056 If the value has a metatable with a <code>__tostring</code> field, 7057 then <code>luaL_tolstring</code> calls the corresponding metamethod 7058 with the value as argument, 7059 and uses the result of the call as its result. 7060 7061 7062 7063 7064 7065 <hr><h3><a name="luaL_traceback"><code>luaL_traceback</code></a></h3><p> 7066 <span class="apii">[-0, +1, <em>m</em>]</span> 7067 <pre>void luaL_traceback (lua_State *L, lua_State *L1, const char *msg, 7068 int level);</pre> 7069 7070 <p> 7071 Creates and pushes a traceback of the stack <code>L1</code>. 7072 If <code>msg</code> is not <code>NULL</code> it is appended 7073 at the beginning of the traceback. 7074 The <code>level</code> parameter tells at which level 7075 to start the traceback. 7076 7077 7078 7079 7080 7081 <hr><h3><a name="luaL_typename"><code>luaL_typename</code></a></h3><p> 7082 <span class="apii">[-0, +0, –]</span> 7083 <pre>const char *luaL_typename (lua_State *L, int index);</pre> 7084 7085 <p> 7086 Returns the name of the type of the value at the given index. 7087 7088 7089 7090 7091 7092 <hr><h3><a name="luaL_unref"><code>luaL_unref</code></a></h3><p> 7093 <span class="apii">[-0, +0, –]</span> 7094 <pre>void luaL_unref (lua_State *L, int t, int ref);</pre> 7095 7096 <p> 7097 Releases reference <code>ref</code> from the table at index <code>t</code> 7098 (see <a href="#luaL_ref"><code>luaL_ref</code></a>). 7099 The entry is removed from the table, 7100 so that the referred object can be collected. 7101 The reference <code>ref</code> is also freed to be used again. 7102 7103 7104 <p> 7105 If <code>ref</code> is <a href="#pdf-LUA_NOREF"><code>LUA_NOREF</code></a> or <a href="#pdf-LUA_REFNIL"><code>LUA_REFNIL</code></a>, 7106 <a href="#luaL_unref"><code>luaL_unref</code></a> does nothing. 7107 7108 7109 7110 7111 7112 <hr><h3><a name="luaL_where"><code>luaL_where</code></a></h3><p> 7113 <span class="apii">[-0, +1, <em>m</em>]</span> 7114 <pre>void luaL_where (lua_State *L, int lvl);</pre> 7115 7116 <p> 7117 Pushes onto the stack a string identifying the current position 7118 of the control at level <code>lvl</code> in the call stack. 7119 Typically this string has the following format: 7120 7121 <pre> 7122 <em>chunkname</em>:<em>currentline</em>: 7123 </pre><p> 7124 Level 0 is the running function, 7125 level 1 is the function that called the running function, 7126 etc. 7127 7128 7129 <p> 7130 This function is used to build a prefix for error messages. 7131 7132 7133 7134 7135 7136 7137 7138 <h1>6 – <a name="6">Standard Libraries</a></h1> 7139 7140 <p> 7141 The standard Lua libraries provide useful functions 7142 that are implemented directly through the C API. 7143 Some of these functions provide essential services to the language 7144 (e.g., <a href="#pdf-type"><code>type</code></a> and <a href="#pdf-getmetatable"><code>getmetatable</code></a>); 7145 others provide access to "outside" services (e.g., I/O); 7146 and others could be implemented in Lua itself, 7147 but are quite useful or have critical performance requirements that 7148 deserve an implementation in C (e.g., <a href="#pdf-table.sort"><code>table.sort</code></a>). 7149 7150 7151 <p> 7152 All libraries are implemented through the official C API 7153 and are provided as separate C modules. 7154 Currently, Lua has the following standard libraries: 7155 7156 <ul> 7157 7158 <li>basic library (<a href="#6.1">§6.1</a>);</li> 7159 7160 <li>coroutine library (<a href="#6.2">§6.2</a>);</li> 7161 7162 <li>package library (<a href="#6.3">§6.3</a>);</li> 7163 7164 <li>string manipulation (<a href="#6.4">§6.4</a>);</li> 7165 7166 <li>basic UTF-8 support (<a href="#6.5">§6.5</a>);</li> 7167 7168 <li>table manipulation (<a href="#6.6">§6.6</a>);</li> 7169 7170 <li>mathematical functions (<a href="#6.7">§6.7</a>) (sin, log, etc.);</li> 7171 7172 <li>input and output (<a href="#6.8">§6.8</a>);</li> 7173 7174 <li>operating system facilities (<a href="#6.9">§6.9</a>);</li> 7175 7176 <li>debug facilities (<a href="#6.10">§6.10</a>).</li> 7177 7178 </ul><p> 7179 Except for the basic and the package libraries, 7180 each library provides all its functions as fields of a global table 7181 or as methods of its objects. 7182 7183 7184 <p> 7185 To have access to these libraries, 7186 the C host program should call the <a href="#luaL_openlibs"><code>luaL_openlibs</code></a> function, 7187 which opens all standard libraries. 7188 Alternatively, 7189 the host program can open them individually by using 7190 <a href="#luaL_requiref"><code>luaL_requiref</code></a> to call 7191 <a name="pdf-luaopen_base"><code>luaopen_base</code></a> (for the basic library), 7192 <a name="pdf-luaopen_package"><code>luaopen_package</code></a> (for the package library), 7193 <a name="pdf-luaopen_coroutine"><code>luaopen_coroutine</code></a> (for the coroutine library), 7194 <a name="pdf-luaopen_string"><code>luaopen_string</code></a> (for the string library), 7195 <a name="pdf-luaopen_utf8"><code>luaopen_utf8</code></a> (for the UTF8 library), 7196 <a name="pdf-luaopen_table"><code>luaopen_table</code></a> (for the table library), 7197 <a name="pdf-luaopen_math"><code>luaopen_math</code></a> (for the mathematical library), 7198 <a name="pdf-luaopen_io"><code>luaopen_io</code></a> (for the I/O library), 7199 <a name="pdf-luaopen_os"><code>luaopen_os</code></a> (for the operating system library), 7200 and <a name="pdf-luaopen_debug"><code>luaopen_debug</code></a> (for the debug library). 7201 These functions are declared in <a name="pdf-lualib.h"><code>lualib.h</code></a>. 7202 7203 7204 7205 <h2>6.1 – <a name="6.1">Basic Functions</a></h2> 7206 7207 <p> 7208 The basic library provides core functions to Lua. 7209 If you do not include this library in your application, 7210 you should check carefully whether you need to provide 7211 implementations for some of its facilities. 7212 7213 7214 <p> 7215 <hr><h3><a name="pdf-assert"><code>assert (v [, message])</code></a></h3> 7216 7217 7218 <p> 7219 Calls <a href="#pdf-error"><code>error</code></a> if 7220 the value of its argument <code>v</code> is false (i.e., <b>nil</b> or <b>false</b>); 7221 otherwise, returns all its arguments. 7222 In case of error, 7223 <code>message</code> is the error object; 7224 when absent, it defaults to "<code>assertion failed!</code>" 7225 7226 7227 7228 7229 <p> 7230 <hr><h3><a name="pdf-collectgarbage"><code>collectgarbage ([opt [, arg]])</code></a></h3> 7231 7232 7233 <p> 7234 This function is a generic interface to the garbage collector. 7235 It performs different functions according to its first argument, <code>opt</code>: 7236 7237 <ul> 7238 7239 <li><b>"<code>collect</code>": </b> 7240 performs a full garbage-collection cycle. 7241 This is the default option. 7242 </li> 7243 7244 <li><b>"<code>stop</code>": </b> 7245 stops automatic execution of the garbage collector. 7246 The collector will run only when explicitly invoked, 7247 until a call to restart it. 7248 </li> 7249 7250 <li><b>"<code>restart</code>": </b> 7251 restarts automatic execution of the garbage collector. 7252 </li> 7253 7254 <li><b>"<code>count</code>": </b> 7255 returns the total memory in use by Lua in Kbytes. 7256 The value has a fractional part, 7257 so that it multiplied by 1024 7258 gives the exact number of bytes in use by Lua 7259 (except for overflows). 7260 </li> 7261 7262 <li><b>"<code>step</code>": </b> 7263 performs a garbage-collection step. 7264 The step "size" is controlled by <code>arg</code>. 7265 With a zero value, 7266 the collector will perform one basic (indivisible) step. 7267 For non-zero values, 7268 the collector will perform as if that amount of memory 7269 (in KBytes) had been allocated by Lua. 7270 Returns <b>true</b> if the step finished a collection cycle. 7271 </li> 7272 7273 <li><b>"<code>setpause</code>": </b> 7274 sets <code>arg</code> as the new value for the <em>pause</em> of 7275 the collector (see <a href="#2.5">§2.5</a>). 7276 Returns the previous value for <em>pause</em>. 7277 </li> 7278 7279 <li><b>"<code>setstepmul</code>": </b> 7280 sets <code>arg</code> as the new value for the <em>step multiplier</em> of 7281 the collector (see <a href="#2.5">§2.5</a>). 7282 Returns the previous value for <em>step</em>. 7283 </li> 7284 7285 <li><b>"<code>isrunning</code>": </b> 7286 returns a boolean that tells whether the collector is running 7287 (i.e., not stopped). 7288 </li> 7289 7290 </ul> 7291 7292 7293 7294 <p> 7295 <hr><h3><a name="pdf-dofile"><code>dofile ([filename])</code></a></h3> 7296 Opens the named file and executes its contents as a Lua chunk. 7297 When called without arguments, 7298 <code>dofile</code> executes the contents of the standard input (<code>stdin</code>). 7299 Returns all values returned by the chunk. 7300 In case of errors, <code>dofile</code> propagates the error 7301 to its caller (that is, <code>dofile</code> does not run in protected mode). 7302 7303 7304 7305 7306 <p> 7307 <hr><h3><a name="pdf-error"><code>error (message [, level])</code></a></h3> 7308 Terminates the last protected function called 7309 and returns <code>message</code> as the error object. 7310 Function <code>error</code> never returns. 7311 7312 7313 <p> 7314 Usually, <code>error</code> adds some information about the error position 7315 at the beginning of the message, if the message is a string. 7316 The <code>level</code> argument specifies how to get the error position. 7317 With level 1 (the default), the error position is where the 7318 <code>error</code> function was called. 7319 Level 2 points the error to where the function 7320 that called <code>error</code> was called; and so on. 7321 Passing a level 0 avoids the addition of error position information 7322 to the message. 7323 7324 7325 7326 7327 <p> 7328 <hr><h3><a name="pdf-_G"><code>_G</code></a></h3> 7329 A global variable (not a function) that 7330 holds the global environment (see <a href="#2.2">§2.2</a>). 7331 Lua itself does not use this variable; 7332 changing its value does not affect any environment, 7333 nor vice versa. 7334 7335 7336 7337 7338 <p> 7339 <hr><h3><a name="pdf-getmetatable"><code>getmetatable (object)</code></a></h3> 7340 7341 7342 <p> 7343 If <code>object</code> does not have a metatable, returns <b>nil</b>. 7344 Otherwise, 7345 if the object's metatable has a <code>__metatable</code> field, 7346 returns the associated value. 7347 Otherwise, returns the metatable of the given object. 7348 7349 7350 7351 7352 <p> 7353 <hr><h3><a name="pdf-ipairs"><code>ipairs (t)</code></a></h3> 7354 7355 7356 <p> 7357 Returns three values (an iterator function, the table <code>t</code>, and 0) 7358 so that the construction 7359 7360 <pre> 7361 for i,v in ipairs(t) do <em>body</em> end 7362 </pre><p> 7363 will iterate over the key–value pairs 7364 (<code>1,t[1]</code>), (<code>2,t[2]</code>), ..., 7365 up to the first nil value. 7366 7367 7368 7369 7370 <p> 7371 <hr><h3><a name="pdf-load"><code>load (chunk [, chunkname [, mode [, env]]])</code></a></h3> 7372 7373 7374 <p> 7375 Loads a chunk. 7376 7377 7378 <p> 7379 If <code>chunk</code> is a string, the chunk is this string. 7380 If <code>chunk</code> is a function, 7381 <code>load</code> calls it repeatedly to get the chunk pieces. 7382 Each call to <code>chunk</code> must return a string that concatenates 7383 with previous results. 7384 A return of an empty string, <b>nil</b>, or no value signals the end of the chunk. 7385 7386 7387 <p> 7388 If there are no syntactic errors, 7389 returns the compiled chunk as a function; 7390 otherwise, returns <b>nil</b> plus the error message. 7391 7392 7393 <p> 7394 If the resulting function has upvalues, 7395 the first upvalue is set to the value of <code>env</code>, 7396 if that parameter is given, 7397 or to the value of the global environment. 7398 Other upvalues are initialized with <b>nil</b>. 7399 (When you load a main chunk, 7400 the resulting function will always have exactly one upvalue, 7401 the <code>_ENV</code> variable (see <a href="#2.2">§2.2</a>). 7402 However, 7403 when you load a binary chunk created from a function (see <a href="#pdf-string.dump"><code>string.dump</code></a>), 7404 the resulting function can have an arbitrary number of upvalues.) 7405 All upvalues are fresh, that is, 7406 they are not shared with any other function. 7407 7408 7409 <p> 7410 <code>chunkname</code> is used as the name of the chunk for error messages 7411 and debug information (see <a href="#4.9">§4.9</a>). 7412 When absent, 7413 it defaults to <code>chunk</code>, if <code>chunk</code> is a string, 7414 or to "<code>=(load)</code>" otherwise. 7415 7416 7417 <p> 7418 The string <code>mode</code> controls whether the chunk can be text or binary 7419 (that is, a precompiled chunk). 7420 It may be the string "<code>b</code>" (only binary chunks), 7421 "<code>t</code>" (only text chunks), 7422 or "<code>bt</code>" (both binary and text). 7423 The default is "<code>bt</code>". 7424 7425 7426 <p> 7427 Lua does not check the consistency of binary chunks. 7428 Maliciously crafted binary chunks can crash 7429 the interpreter. 7430 7431 7432 7433 7434 <p> 7435 <hr><h3><a name="pdf-loadfile"><code>loadfile ([filename [, mode [, env]]])</code></a></h3> 7436 7437 7438 <p> 7439 Similar to <a href="#pdf-load"><code>load</code></a>, 7440 but gets the chunk from file <code>filename</code> 7441 or from the standard input, 7442 if no file name is given. 7443 7444 7445 7446 7447 <p> 7448 <hr><h3><a name="pdf-next"><code>next (table [, index])</code></a></h3> 7449 7450 7451 <p> 7452 Allows a program to traverse all fields of a table. 7453 Its first argument is a table and its second argument 7454 is an index in this table. 7455 <code>next</code> returns the next index of the table 7456 and its associated value. 7457 When called with <b>nil</b> as its second argument, 7458 <code>next</code> returns an initial index 7459 and its associated value. 7460 When called with the last index, 7461 or with <b>nil</b> in an empty table, 7462 <code>next</code> returns <b>nil</b>. 7463 If the second argument is absent, then it is interpreted as <b>nil</b>. 7464 In particular, 7465 you can use <code>next(t)</code> to check whether a table is empty. 7466 7467 7468 <p> 7469 The order in which the indices are enumerated is not specified, 7470 <em>even for numeric indices</em>. 7471 (To traverse a table in numerical order, 7472 use a numerical <b>for</b>.) 7473 7474 7475 <p> 7476 The behavior of <code>next</code> is undefined if, 7477 during the traversal, 7478 you assign any value to a non-existent field in the table. 7479 You may however modify existing fields. 7480 In particular, you may clear existing fields. 7481 7482 7483 7484 7485 <p> 7486 <hr><h3><a name="pdf-pairs"><code>pairs (t)</code></a></h3> 7487 7488 7489 <p> 7490 If <code>t</code> has a metamethod <code>__pairs</code>, 7491 calls it with <code>t</code> as argument and returns the first three 7492 results from the call. 7493 7494 7495 <p> 7496 Otherwise, 7497 returns three values: the <a href="#pdf-next"><code>next</code></a> function, the table <code>t</code>, and <b>nil</b>, 7498 so that the construction 7499 7500 <pre> 7501 for k,v in pairs(t) do <em>body</em> end 7502 </pre><p> 7503 will iterate over all key–value pairs of table <code>t</code>. 7504 7505 7506 <p> 7507 See function <a href="#pdf-next"><code>next</code></a> for the caveats of modifying 7508 the table during its traversal. 7509 7510 7511 7512 7513 <p> 7514 <hr><h3><a name="pdf-pcall"><code>pcall (f [, arg1, ···])</code></a></h3> 7515 7516 7517 <p> 7518 Calls function <code>f</code> with 7519 the given arguments in <em>protected mode</em>. 7520 This means that any error inside <code>f</code> is not propagated; 7521 instead, <code>pcall</code> catches the error 7522 and returns a status code. 7523 Its first result is the status code (a boolean), 7524 which is true if the call succeeds without errors. 7525 In such case, <code>pcall</code> also returns all results from the call, 7526 after this first result. 7527 In case of any error, <code>pcall</code> returns <b>false</b> plus the error message. 7528 7529 7530 7531 7532 <p> 7533 <hr><h3><a name="pdf-print"><code>print (···)</code></a></h3> 7534 Receives any number of arguments 7535 and prints their values to <code>stdout</code>, 7536 using the <a href="#pdf-tostring"><code>tostring</code></a> function to convert each argument to a string. 7537 <code>print</code> is not intended for formatted output, 7538 but only as a quick way to show a value, 7539 for instance for debugging. 7540 For complete control over the output, 7541 use <a href="#pdf-string.format"><code>string.format</code></a> and <a href="#pdf-io.write"><code>io.write</code></a>. 7542 7543 7544 7545 7546 <p> 7547 <hr><h3><a name="pdf-rawequal"><code>rawequal (v1, v2)</code></a></h3> 7548 Checks whether <code>v1</code> is equal to <code>v2</code>, 7549 without invoking the <code>__eq</code> metamethod. 7550 Returns a boolean. 7551 7552 7553 7554 7555 <p> 7556 <hr><h3><a name="pdf-rawget"><code>rawget (table, index)</code></a></h3> 7557 Gets the real value of <code>table[index]</code>, 7558 without invoking the <code>__index</code> metamethod. 7559 <code>table</code> must be a table; 7560 <code>index</code> may be any value. 7561 7562 7563 7564 7565 <p> 7566 <hr><h3><a name="pdf-rawlen"><code>rawlen (v)</code></a></h3> 7567 Returns the length of the object <code>v</code>, 7568 which must be a table or a string, 7569 without invoking the <code>__len</code> metamethod. 7570 Returns an integer. 7571 7572 7573 7574 7575 <p> 7576 <hr><h3><a name="pdf-rawset"><code>rawset (table, index, value)</code></a></h3> 7577 Sets the real value of <code>table[index]</code> to <code>value</code>, 7578 without invoking the <code>__newindex</code> metamethod. 7579 <code>table</code> must be a table, 7580 <code>index</code> any value different from <b>nil</b> and NaN, 7581 and <code>value</code> any Lua value. 7582 7583 7584 <p> 7585 This function returns <code>table</code>. 7586 7587 7588 7589 7590 <p> 7591 <hr><h3><a name="pdf-select"><code>select (index, ···)</code></a></h3> 7592 7593 7594 <p> 7595 If <code>index</code> is a number, 7596 returns all arguments after argument number <code>index</code>; 7597 a negative number indexes from the end (-1 is the last argument). 7598 Otherwise, <code>index</code> must be the string <code>"#"</code>, 7599 and <code>select</code> returns the total number of extra arguments it received. 7600 7601 7602 7603 7604 <p> 7605 <hr><h3><a name="pdf-setmetatable"><code>setmetatable (table, metatable)</code></a></h3> 7606 7607 7608 <p> 7609 Sets the metatable for the given table. 7610 (To change the metatable of other types from Lua code, 7611 you must use the debug library (<a href="#6.10">§6.10</a>).) 7612 If <code>metatable</code> is <b>nil</b>, 7613 removes the metatable of the given table. 7614 If the original metatable has a <code>__metatable</code> field, 7615 raises an error. 7616 7617 7618 <p> 7619 This function returns <code>table</code>. 7620 7621 7622 7623 7624 <p> 7625 <hr><h3><a name="pdf-tonumber"><code>tonumber (e [, base])</code></a></h3> 7626 7627 7628 <p> 7629 When called with no <code>base</code>, 7630 <code>tonumber</code> tries to convert its argument to a number. 7631 If the argument is already a number or 7632 a string convertible to a number, 7633 then <code>tonumber</code> returns this number; 7634 otherwise, it returns <b>nil</b>. 7635 7636 7637 <p> 7638 The conversion of strings can result in integers or floats, 7639 according to the lexical conventions of Lua (see <a href="#3.1">§3.1</a>). 7640 (The string may have leading and trailing spaces and a sign.) 7641 7642 7643 <p> 7644 When called with <code>base</code>, 7645 then <code>e</code> must be a string to be interpreted as 7646 an integer numeral in that base. 7647 The base may be any integer between 2 and 36, inclusive. 7648 In bases above 10, the letter '<code>A</code>' (in either upper or lower case) 7649 represents 10, '<code>B</code>' represents 11, and so forth, 7650 with '<code>Z</code>' representing 35. 7651 If the string <code>e</code> is not a valid numeral in the given base, 7652 the function returns <b>nil</b>. 7653 7654 7655 7656 7657 <p> 7658 <hr><h3><a name="pdf-tostring"><code>tostring (v)</code></a></h3> 7659 Receives a value of any type and 7660 converts it to a string in a human-readable format. 7661 (For complete control of how numbers are converted, 7662 use <a href="#pdf-string.format"><code>string.format</code></a>.) 7663 7664 7665 <p> 7666 If the metatable of <code>v</code> has a <code>__tostring</code> field, 7667 then <code>tostring</code> calls the corresponding value 7668 with <code>v</code> as argument, 7669 and uses the result of the call as its result. 7670 7671 7672 7673 7674 <p> 7675 <hr><h3><a name="pdf-type"><code>type (v)</code></a></h3> 7676 Returns the type of its only argument, coded as a string. 7677 The possible results of this function are 7678 "<code>nil</code>" (a string, not the value <b>nil</b>), 7679 "<code>number</code>", 7680 "<code>string</code>", 7681 "<code>boolean</code>", 7682 "<code>table</code>", 7683 "<code>function</code>", 7684 "<code>thread</code>", 7685 and "<code>userdata</code>". 7686 7687 7688 7689 7690 <p> 7691 <hr><h3><a name="pdf-_VERSION"><code>_VERSION</code></a></h3> 7692 7693 7694 <p> 7695 A global variable (not a function) that 7696 holds a string containing the running Lua version. 7697 The current value of this variable is "<code>Lua 5.3</code>". 7698 7699 7700 7701 7702 <p> 7703 <hr><h3><a name="pdf-xpcall"><code>xpcall (f, msgh [, arg1, ···])</code></a></h3> 7704 7705 7706 <p> 7707 This function is similar to <a href="#pdf-pcall"><code>pcall</code></a>, 7708 except that it sets a new message handler <code>msgh</code>. 7709 7710 7711 7712 7713 7714 7715 7716 <h2>6.2 – <a name="6.2">Coroutine Manipulation</a></h2> 7717 7718 <p> 7719 This library comprises the operations to manipulate coroutines, 7720 which come inside the table <a name="pdf-coroutine"><code>coroutine</code></a>. 7721 See <a href="#2.6">§2.6</a> for a general description of coroutines. 7722 7723 7724 <p> 7725 <hr><h3><a name="pdf-coroutine.create"><code>coroutine.create (f)</code></a></h3> 7726 7727 7728 <p> 7729 Creates a new coroutine, with body <code>f</code>. 7730 <code>f</code> must be a function. 7731 Returns this new coroutine, 7732 an object with type <code>"thread"</code>. 7733 7734 7735 7736 7737 <p> 7738 <hr><h3><a name="pdf-coroutine.isyieldable"><code>coroutine.isyieldable ()</code></a></h3> 7739 7740 7741 <p> 7742 Returns true when the running coroutine can yield. 7743 7744 7745 <p> 7746 A running coroutine is yieldable if it is not the main thread and 7747 it is not inside a non-yieldable C function. 7748 7749 7750 7751 7752 <p> 7753 <hr><h3><a name="pdf-coroutine.resume"><code>coroutine.resume (co [, val1, ···])</code></a></h3> 7754 7755 7756 <p> 7757 Starts or continues the execution of coroutine <code>co</code>. 7758 The first time you resume a coroutine, 7759 it starts running its body. 7760 The values <code>val1</code>, ... are passed 7761 as the arguments to the body function. 7762 If the coroutine has yielded, 7763 <code>resume</code> restarts it; 7764 the values <code>val1</code>, ... are passed 7765 as the results from the yield. 7766 7767 7768 <p> 7769 If the coroutine runs without any errors, 7770 <code>resume</code> returns <b>true</b> plus any values passed to <code>yield</code> 7771 (when the coroutine yields) or any values returned by the body function 7772 (when the coroutine terminates). 7773 If there is any error, 7774 <code>resume</code> returns <b>false</b> plus the error message. 7775 7776 7777 7778 7779 <p> 7780 <hr><h3><a name="pdf-coroutine.running"><code>coroutine.running ()</code></a></h3> 7781 7782 7783 <p> 7784 Returns the running coroutine plus a boolean, 7785 true when the running coroutine is the main one. 7786 7787 7788 7789 7790 <p> 7791 <hr><h3><a name="pdf-coroutine.status"><code>coroutine.status (co)</code></a></h3> 7792 7793 7794 <p> 7795 Returns the status of coroutine <code>co</code>, as a string: 7796 <code>"running"</code>, 7797 if the coroutine is running (that is, it called <code>status</code>); 7798 <code>"suspended"</code>, if the coroutine is suspended in a call to <code>yield</code>, 7799 or if it has not started running yet; 7800 <code>"normal"</code> if the coroutine is active but not running 7801 (that is, it has resumed another coroutine); 7802 and <code>"dead"</code> if the coroutine has finished its body function, 7803 or if it has stopped with an error. 7804 7805 7806 7807 7808 <p> 7809 <hr><h3><a name="pdf-coroutine.wrap"><code>coroutine.wrap (f)</code></a></h3> 7810 7811 7812 <p> 7813 Creates a new coroutine, with body <code>f</code>. 7814 <code>f</code> must be a function. 7815 Returns a function that resumes the coroutine each time it is called. 7816 Any arguments passed to the function behave as the 7817 extra arguments to <code>resume</code>. 7818 Returns the same values returned by <code>resume</code>, 7819 except the first boolean. 7820 In case of error, propagates the error. 7821 7822 7823 7824 7825 <p> 7826 <hr><h3><a name="pdf-coroutine.yield"><code>coroutine.yield (···)</code></a></h3> 7827 7828 7829 <p> 7830 Suspends the execution of the calling coroutine. 7831 Any arguments to <code>yield</code> are passed as extra results to <code>resume</code>. 7832 7833 7834 7835 7836 7837 7838 7839 <h2>6.3 – <a name="6.3">Modules</a></h2> 7840 7841 <p> 7842 The package library provides basic 7843 facilities for loading modules in Lua. 7844 It exports one function directly in the global environment: 7845 <a href="#pdf-require"><code>require</code></a>. 7846 Everything else is exported in a table <a name="pdf-package"><code>package</code></a>. 7847 7848 7849 <p> 7850 <hr><h3><a name="pdf-require"><code>require (modname)</code></a></h3> 7851 7852 7853 <p> 7854 Loads the given module. 7855 The function starts by looking into the <a href="#pdf-package.loaded"><code>package.loaded</code></a> table 7856 to determine whether <code>modname</code> is already loaded. 7857 If it is, then <code>require</code> returns the value stored 7858 at <code>package.loaded[modname]</code>. 7859 Otherwise, it tries to find a <em>loader</em> for the module. 7860 7861 7862 <p> 7863 To find a loader, 7864 <code>require</code> is guided by the <a href="#pdf-package.searchers"><code>package.searchers</code></a> sequence. 7865 By changing this sequence, 7866 we can change how <code>require</code> looks for a module. 7867 The following explanation is based on the default configuration 7868 for <a href="#pdf-package.searchers"><code>package.searchers</code></a>. 7869 7870 7871 <p> 7872 First <code>require</code> queries <code>package.preload[modname]</code>. 7873 If it has a value, 7874 this value (which must be a function) is the loader. 7875 Otherwise <code>require</code> searches for a Lua loader using the 7876 path stored in <a href="#pdf-package.path"><code>package.path</code></a>. 7877 If that also fails, it searches for a C loader using the 7878 path stored in <a href="#pdf-package.cpath"><code>package.cpath</code></a>. 7879 If that also fails, 7880 it tries an <em>all-in-one</em> loader (see <a href="#pdf-package.searchers"><code>package.searchers</code></a>). 7881 7882 7883 <p> 7884 Once a loader is found, 7885 <code>require</code> calls the loader with two arguments: 7886 <code>modname</code> and an extra value dependent on how it got the loader. 7887 (If the loader came from a file, 7888 this extra value is the file name.) 7889 If the loader returns any non-nil value, 7890 <code>require</code> assigns the returned value to <code>package.loaded[modname]</code>. 7891 If the loader does not return a non-nil value and 7892 has not assigned any value to <code>package.loaded[modname]</code>, 7893 then <code>require</code> assigns <b>true</b> to this entry. 7894 In any case, <code>require</code> returns the 7895 final value of <code>package.loaded[modname]</code>. 7896 7897 7898 <p> 7899 If there is any error loading or running the module, 7900 or if it cannot find any loader for the module, 7901 then <code>require</code> raises an error. 7902 7903 7904 7905 7906 <p> 7907 <hr><h3><a name="pdf-package.config"><code>package.config</code></a></h3> 7908 7909 7910 <p> 7911 A string describing some compile-time configurations for packages. 7912 This string is a sequence of lines: 7913 7914 <ul> 7915 7916 <li>The first line is the directory separator string. 7917 Default is '<code>\</code>' for Windows and '<code>/</code>' for all other systems.</li> 7918 7919 <li>The second line is the character that separates templates in a path. 7920 Default is '<code>;</code>'.</li> 7921 7922 <li>The third line is the string that marks the 7923 substitution points in a template. 7924 Default is '<code>?</code>'.</li> 7925 7926 <li>The fourth line is a string that, in a path in Windows, 7927 is replaced by the executable's directory. 7928 Default is '<code>!</code>'.</li> 7929 7930 <li>The fifth line is a mark to ignore all text after it 7931 when building the <code>luaopen_</code> function name. 7932 Default is '<code>-</code>'.</li> 7933 7934 </ul> 7935 7936 7937 7938 <p> 7939 <hr><h3><a name="pdf-package.cpath"><code>package.cpath</code></a></h3> 7940 7941 7942 <p> 7943 The path used by <a href="#pdf-require"><code>require</code></a> to search for a C loader. 7944 7945 7946 <p> 7947 Lua initializes the C path <a href="#pdf-package.cpath"><code>package.cpath</code></a> in the same way 7948 it initializes the Lua path <a href="#pdf-package.path"><code>package.path</code></a>, 7949 using the environment variable <a name="pdf-LUA_CPATH_5_3"><code>LUA_CPATH_5_3</code></a>, 7950 or the environment variable <a name="pdf-LUA_CPATH"><code>LUA_CPATH</code></a>, 7951 or a default path defined in <code>luaconf.h</code>. 7952 7953 7954 7955 7956 <p> 7957 <hr><h3><a name="pdf-package.loaded"><code>package.loaded</code></a></h3> 7958 7959 7960 <p> 7961 A table used by <a href="#pdf-require"><code>require</code></a> to control which 7962 modules are already loaded. 7963 When you require a module <code>modname</code> and 7964 <code>package.loaded[modname]</code> is not false, 7965 <a href="#pdf-require"><code>require</code></a> simply returns the value stored there. 7966 7967 7968 <p> 7969 This variable is only a reference to the real table; 7970 assignments to this variable do not change the 7971 table used by <a href="#pdf-require"><code>require</code></a>. 7972 7973 7974 7975 7976 <p> 7977 <hr><h3><a name="pdf-package.loadlib"><code>package.loadlib (libname, funcname)</code></a></h3> 7978 7979 7980 <p> 7981 Dynamically links the host program with the C library <code>libname</code>. 7982 7983 7984 <p> 7985 If <code>funcname</code> is "<code>*</code>", 7986 then it only links with the library, 7987 making the symbols exported by the library 7988 available to other dynamically linked libraries. 7989 Otherwise, 7990 it looks for a function <code>funcname</code> inside the library 7991 and returns this function as a C function. 7992 So, <code>funcname</code> must follow the <a href="#lua_CFunction"><code>lua_CFunction</code></a> prototype 7993 (see <a href="#lua_CFunction"><code>lua_CFunction</code></a>). 7994 7995 7996 <p> 7997 This is a low-level function. 7998 It completely bypasses the package and module system. 7999 Unlike <a href="#pdf-require"><code>require</code></a>, 8000 it does not perform any path searching and 8001 does not automatically adds extensions. 8002 <code>libname</code> must be the complete file name of the C library, 8003 including if necessary a path and an extension. 8004 <code>funcname</code> must be the exact name exported by the C library 8005 (which may depend on the C compiler and linker used). 8006 8007 8008 <p> 8009 This function is not supported by Standard C. 8010 As such, it is only available on some platforms 8011 (Windows, Linux, Mac OS X, Solaris, BSD, 8012 plus other Unix systems that support the <code>dlfcn</code> standard). 8013 8014 8015 8016 8017 <p> 8018 <hr><h3><a name="pdf-package.path"><code>package.path</code></a></h3> 8019 8020 8021 <p> 8022 The path used by <a href="#pdf-require"><code>require</code></a> to search for a Lua loader. 8023 8024 8025 <p> 8026 At start-up, Lua initializes this variable with 8027 the value of the environment variable <a name="pdf-LUA_PATH_5_3"><code>LUA_PATH_5_3</code></a> or 8028 the environment variable <a name="pdf-LUA_PATH"><code>LUA_PATH</code></a> or 8029 with a default path defined in <code>luaconf.h</code>, 8030 if those environment variables are not defined. 8031 Any "<code>;;</code>" in the value of the environment variable 8032 is replaced by the default path. 8033 8034 8035 8036 8037 <p> 8038 <hr><h3><a name="pdf-package.preload"><code>package.preload</code></a></h3> 8039 8040 8041 <p> 8042 A table to store loaders for specific modules 8043 (see <a href="#pdf-require"><code>require</code></a>). 8044 8045 8046 <p> 8047 This variable is only a reference to the real table; 8048 assignments to this variable do not change the 8049 table used by <a href="#pdf-require"><code>require</code></a>. 8050 8051 8052 8053 8054 <p> 8055 <hr><h3><a name="pdf-package.searchers"><code>package.searchers</code></a></h3> 8056 8057 8058 <p> 8059 A table used by <a href="#pdf-require"><code>require</code></a> to control how to load modules. 8060 8061 8062 <p> 8063 Each entry in this table is a <em>searcher function</em>. 8064 When looking for a module, 8065 <a href="#pdf-require"><code>require</code></a> calls each of these searchers in ascending order, 8066 with the module name (the argument given to <a href="#pdf-require"><code>require</code></a>) as its 8067 sole parameter. 8068 The function can return another function (the module <em>loader</em>) 8069 plus an extra value that will be passed to that loader, 8070 or a string explaining why it did not find that module 8071 (or <b>nil</b> if it has nothing to say). 8072 8073 8074 <p> 8075 Lua initializes this table with four searcher functions. 8076 8077 8078 <p> 8079 The first searcher simply looks for a loader in the 8080 <a href="#pdf-package.preload"><code>package.preload</code></a> table. 8081 8082 8083 <p> 8084 The second searcher looks for a loader as a Lua library, 8085 using the path stored at <a href="#pdf-package.path"><code>package.path</code></a>. 8086 The search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. 8087 8088 8089 <p> 8090 The third searcher looks for a loader as a C library, 8091 using the path given by the variable <a href="#pdf-package.cpath"><code>package.cpath</code></a>. 8092 Again, 8093 the search is done as described in function <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. 8094 For instance, 8095 if the C path is the string 8096 8097 <pre> 8098 "./?.so;./?.dll;/usr/local/?/init.so" 8099 </pre><p> 8100 the searcher for module <code>foo</code> 8101 will try to open the files <code>./foo.so</code>, <code>./foo.dll</code>, 8102 and <code>/usr/local/foo/init.so</code>, in that order. 8103 Once it finds a C library, 8104 this searcher first uses a dynamic link facility to link the 8105 application with the library. 8106 Then it tries to find a C function inside the library to 8107 be used as the loader. 8108 The name of this C function is the string "<code>luaopen_</code>" 8109 concatenated with a copy of the module name where each dot 8110 is replaced by an underscore. 8111 Moreover, if the module name has a hyphen, 8112 its suffix after (and including) the first hyphen is removed. 8113 For instance, if the module name is <code>a.b.c-v2.1</code>, 8114 the function name will be <code>luaopen_a_b_c</code>. 8115 8116 8117 <p> 8118 The fourth searcher tries an <em>all-in-one loader</em>. 8119 It searches the C path for a library for 8120 the root name of the given module. 8121 For instance, when requiring <code>a.b.c</code>, 8122 it will search for a C library for <code>a</code>. 8123 If found, it looks into it for an open function for 8124 the submodule; 8125 in our example, that would be <code>luaopen_a_b_c</code>. 8126 With this facility, a package can pack several C submodules 8127 into one single library, 8128 with each submodule keeping its original open function. 8129 8130 8131 <p> 8132 All searchers except the first one (preload) return as the extra value 8133 the file name where the module was found, 8134 as returned by <a href="#pdf-package.searchpath"><code>package.searchpath</code></a>. 8135 The first searcher returns no extra value. 8136 8137 8138 8139 8140 <p> 8141 <hr><h3><a name="pdf-package.searchpath"><code>package.searchpath (name, path [, sep [, rep]])</code></a></h3> 8142 8143 8144 <p> 8145 Searches for the given <code>name</code> in the given <code>path</code>. 8146 8147 8148 <p> 8149 A path is a string containing a sequence of 8150 <em>templates</em> separated by semicolons. 8151 For each template, 8152 the function replaces each interrogation mark (if any) 8153 in the template with a copy of <code>name</code> 8154 wherein all occurrences of <code>sep</code> 8155 (a dot, by default) 8156 were replaced by <code>rep</code> 8157 (the system's directory separator, by default), 8158 and then tries to open the resulting file name. 8159 8160 8161 <p> 8162 For instance, if the path is the string 8163 8164 <pre> 8165 "./?.lua;./?.lc;/usr/local/?/init.lua" 8166 </pre><p> 8167 the search for the name <code>foo.a</code> 8168 will try to open the files 8169 <code>./foo/a.lua</code>, <code>./foo/a.lc</code>, and 8170 <code>/usr/local/foo/a/init.lua</code>, in that order. 8171 8172 8173 <p> 8174 Returns the resulting name of the first file that it can 8175 open in read mode (after closing the file), 8176 or <b>nil</b> plus an error message if none succeeds. 8177 (This error message lists all file names it tried to open.) 8178 8179 8180 8181 8182 8183 8184 8185 <h2>6.4 – <a name="6.4">String Manipulation</a></h2> 8186 8187 <p> 8188 This library provides generic functions for string manipulation, 8189 such as finding and extracting substrings, and pattern matching. 8190 When indexing a string in Lua, the first character is at position 1 8191 (not at 0, as in C). 8192 Indices are allowed to be negative and are interpreted as indexing backwards, 8193 from the end of the string. 8194 Thus, the last character is at position -1, and so on. 8195 8196 8197 <p> 8198 The string library provides all its functions inside the table 8199 <a name="pdf-string"><code>string</code></a>. 8200 It also sets a metatable for strings 8201 where the <code>__index</code> field points to the <code>string</code> table. 8202 Therefore, you can use the string functions in object-oriented style. 8203 For instance, <code>string.byte(s,i)</code> 8204 can be written as <code>s:byte(i)</code>. 8205 8206 8207 <p> 8208 The string library assumes one-byte character encodings. 8209 8210 8211 <p> 8212 <hr><h3><a name="pdf-string.byte"><code>string.byte (s [, i [, j]])</code></a></h3> 8213 Returns the internal numeric codes of the characters <code>s[i]</code>, 8214 <code>s[i+1]</code>, ..., <code>s[j]</code>. 8215 The default value for <code>i</code> is 1; 8216 the default value for <code>j</code> is <code>i</code>. 8217 These indices are corrected 8218 following the same rules of function <a href="#pdf-string.sub"><code>string.sub</code></a>. 8219 8220 8221 <p> 8222 Numeric codes are not necessarily portable across platforms. 8223 8224 8225 8226 8227 <p> 8228 <hr><h3><a name="pdf-string.char"><code>string.char (···)</code></a></h3> 8229 Receives zero or more integers. 8230 Returns a string with length equal to the number of arguments, 8231 in which each character has the internal numeric code equal 8232 to its corresponding argument. 8233 8234 8235 <p> 8236 Numeric codes are not necessarily portable across platforms. 8237 8238 8239 8240 8241 <p> 8242 <hr><h3><a name="pdf-string.dump"><code>string.dump (function [, strip])</code></a></h3> 8243 8244 8245 <p> 8246 Returns a string containing a binary representation 8247 (a <em>binary chunk</em>) 8248 of the given function, 8249 so that a later <a href="#pdf-load"><code>load</code></a> on this string returns 8250 a copy of the function (but with new upvalues). 8251 If <code>strip</code> is a true value, 8252 the binary representation may not include all debug information 8253 about the function, 8254 to save space. 8255 8256 8257 <p> 8258 Functions with upvalues have only their number of upvalues saved. 8259 When (re)loaded, 8260 those upvalues receive fresh instances containing <b>nil</b>. 8261 (You can use the debug library to serialize 8262 and reload the upvalues of a function 8263 in a way adequate to your needs.) 8264 8265 8266 8267 8268 <p> 8269 <hr><h3><a name="pdf-string.find"><code>string.find (s, pattern [, init [, plain]])</code></a></h3> 8270 8271 8272 <p> 8273 Looks for the first match of 8274 <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) in the string <code>s</code>. 8275 If it finds a match, then <code>find</code> returns the indices of <code>s</code> 8276 where this occurrence starts and ends; 8277 otherwise, it returns <b>nil</b>. 8278 A third, optional numeric argument <code>init</code> specifies 8279 where to start the search; 8280 its default value is 1 and can be negative. 8281 A value of <b>true</b> as a fourth, optional argument <code>plain</code> 8282 turns off the pattern matching facilities, 8283 so the function does a plain "find substring" operation, 8284 with no characters in <code>pattern</code> being considered magic. 8285 Note that if <code>plain</code> is given, then <code>init</code> must be given as well. 8286 8287 8288 <p> 8289 If the pattern has captures, 8290 then in a successful match 8291 the captured values are also returned, 8292 after the two indices. 8293 8294 8295 8296 8297 <p> 8298 <hr><h3><a name="pdf-string.format"><code>string.format (formatstring, ···)</code></a></h3> 8299 8300 8301 <p> 8302 Returns a formatted version of its variable number of arguments 8303 following the description given in its first argument (which must be a string). 8304 The format string follows the same rules as the ISO C function <code>sprintf</code>. 8305 The only differences are that the options/modifiers 8306 <code>*</code>, <code>h</code>, <code>L</code>, <code>l</code>, <code>n</code>, 8307 and <code>p</code> are not supported 8308 and that there is an extra option, <code>q</code>. 8309 8310 8311 <p> 8312 The <code>q</code> option formats a string between double quotes, 8313 using escape sequences when necessary to ensure that 8314 it can safely be read back by the Lua interpreter. 8315 For instance, the call 8316 8317 <pre> 8318 string.format('%q', 'a string with "quotes" and \n new line') 8319 </pre><p> 8320 may produce the string: 8321 8322 <pre> 8323 "a string with \"quotes\" and \ 8324 new line" 8325 </pre> 8326 8327 <p> 8328 Options 8329 <code>A</code>, <code>a</code>, <code>E</code>, <code>e</code>, <code>f</code>, 8330 <code>G</code>, and <code>g</code> all expect a number as argument. 8331 Options <code>c</code>, <code>d</code>, 8332 <code>i</code>, <code>o</code>, <code>u</code>, <code>X</code>, and <code>x</code> 8333 expect an integer. 8334 When Lua is compiled with a C89 compiler, 8335 options <code>A</code> and <code>a</code> (hexadecimal floats) 8336 do not support any modifier (flags, width, length). 8337 8338 8339 <p> 8340 Option <code>s</code> expects a string; 8341 if its argument is not a string, 8342 it is converted to one following the same rules of <a href="#pdf-tostring"><code>tostring</code></a>. 8343 If the option has any modifier (flags, width, length), 8344 the string argument should not contain embedded zeros. 8345 8346 8347 8348 8349 <p> 8350 <hr><h3><a name="pdf-string.gmatch"><code>string.gmatch (s, pattern)</code></a></h3> 8351 Returns an iterator function that, 8352 each time it is called, 8353 returns the next captures from <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) 8354 over the string <code>s</code>. 8355 If <code>pattern</code> specifies no captures, 8356 then the whole match is produced in each call. 8357 8358 8359 <p> 8360 As an example, the following loop 8361 will iterate over all the words from string <code>s</code>, 8362 printing one per line: 8363 8364 <pre> 8365 s = "hello world from Lua" 8366 for w in string.gmatch(s, "%a+") do 8367 print(w) 8368 end 8369 </pre><p> 8370 The next example collects all pairs <code>key=value</code> from the 8371 given string into a table: 8372 8373 <pre> 8374 t = {} 8375 s = "from=world, to=Lua" 8376 for k, v in string.gmatch(s, "(%w+)=(%w+)") do 8377 t[k] = v 8378 end 8379 </pre> 8380 8381 <p> 8382 For this function, a caret '<code>^</code>' at the start of a pattern does not 8383 work as an anchor, as this would prevent the iteration. 8384 8385 8386 8387 8388 <p> 8389 <hr><h3><a name="pdf-string.gsub"><code>string.gsub (s, pattern, repl [, n])</code></a></h3> 8390 Returns a copy of <code>s</code> 8391 in which all (or the first <code>n</code>, if given) 8392 occurrences of the <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) have been 8393 replaced by a replacement string specified by <code>repl</code>, 8394 which can be a string, a table, or a function. 8395 <code>gsub</code> also returns, as its second value, 8396 the total number of matches that occurred. 8397 The name <code>gsub</code> comes from <em>Global SUBstitution</em>. 8398 8399 8400 <p> 8401 If <code>repl</code> is a string, then its value is used for replacement. 8402 The character <code>%</code> works as an escape character: 8403 any sequence in <code>repl</code> of the form <code>%<em>d</em></code>, 8404 with <em>d</em> between 1 and 9, 8405 stands for the value of the <em>d</em>-th captured substring. 8406 The sequence <code>%0</code> stands for the whole match. 8407 The sequence <code>%%</code> stands for a single <code>%</code>. 8408 8409 8410 <p> 8411 If <code>repl</code> is a table, then the table is queried for every match, 8412 using the first capture as the key. 8413 8414 8415 <p> 8416 If <code>repl</code> is a function, then this function is called every time a 8417 match occurs, with all captured substrings passed as arguments, 8418 in order. 8419 8420 8421 <p> 8422 In any case, 8423 if the pattern specifies no captures, 8424 then it behaves as if the whole pattern was inside a capture. 8425 8426 8427 <p> 8428 If the value returned by the table query or by the function call 8429 is a string or a number, 8430 then it is used as the replacement string; 8431 otherwise, if it is <b>false</b> or <b>nil</b>, 8432 then there is no replacement 8433 (that is, the original match is kept in the string). 8434 8435 8436 <p> 8437 Here are some examples: 8438 8439 <pre> 8440 x = string.gsub("hello world", "(%w+)", "%1 %1") 8441 --> x="hello hello world world" 8442 8443 x = string.gsub("hello world", "%w+", "%0 %0", 1) 8444 --> x="hello hello world" 8445 8446 x = string.gsub("hello world from Lua", "(%w+)%s*(%w+)", "%2 %1") 8447 --> x="world hello Lua from" 8448 8449 x = string.gsub("home = $HOME, user = $USER", "%$(%w+)", os.getenv) 8450 --> x="home = /home/roberto, user = roberto" 8451 8452 x = string.gsub("4+5 = $return 4+5$", "%$(.-)%$", function (s) 8453 return load(s)() 8454 end) 8455 --> x="4+5 = 9" 8456 8457 local t = {name="lua", version="5.3"} 8458 x = string.gsub("$name-$version.tar.gz", "%$(%w+)", t) 8459 --> x="lua-5.3.tar.gz" 8460 </pre> 8461 8462 8463 8464 <p> 8465 <hr><h3><a name="pdf-string.len"><code>string.len (s)</code></a></h3> 8466 Receives a string and returns its length. 8467 The empty string <code>""</code> has length 0. 8468 Embedded zeros are counted, 8469 so <code>"a\000bc\000"</code> has length 5. 8470 8471 8472 8473 8474 <p> 8475 <hr><h3><a name="pdf-string.lower"><code>string.lower (s)</code></a></h3> 8476 Receives a string and returns a copy of this string with all 8477 uppercase letters changed to lowercase. 8478 All other characters are left unchanged. 8479 The definition of what an uppercase letter is depends on the current locale. 8480 8481 8482 8483 8484 <p> 8485 <hr><h3><a name="pdf-string.match"><code>string.match (s, pattern [, init])</code></a></h3> 8486 Looks for the first <em>match</em> of 8487 <code>pattern</code> (see <a href="#6.4.1">§6.4.1</a>) in the string <code>s</code>. 8488 If it finds one, then <code>match</code> returns 8489 the captures from the pattern; 8490 otherwise it returns <b>nil</b>. 8491 If <code>pattern</code> specifies no captures, 8492 then the whole match is returned. 8493 A third, optional numeric argument <code>init</code> specifies 8494 where to start the search; 8495 its default value is 1 and can be negative. 8496 8497 8498 8499 8500 <p> 8501 <hr><h3><a name="pdf-string.pack"><code>string.pack (fmt, v1, v2, ···)</code></a></h3> 8502 8503 8504 <p> 8505 Returns a binary string containing the values <code>v1</code>, <code>v2</code>, etc. 8506 packed (that is, serialized in binary form) 8507 according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>). 8508 8509 8510 8511 8512 <p> 8513 <hr><h3><a name="pdf-string.packsize"><code>string.packsize (fmt)</code></a></h3> 8514 8515 8516 <p> 8517 Returns the size of a string resulting from <a href="#pdf-string.pack"><code>string.pack</code></a> 8518 with the given format. 8519 The format string cannot have the variable-length options 8520 '<code>s</code>' or '<code>z</code>' (see <a href="#6.4.2">§6.4.2</a>). 8521 8522 8523 8524 8525 <p> 8526 <hr><h3><a name="pdf-string.rep"><code>string.rep (s, n [, sep])</code></a></h3> 8527 Returns a string that is the concatenation of <code>n</code> copies of 8528 the string <code>s</code> separated by the string <code>sep</code>. 8529 The default value for <code>sep</code> is the empty string 8530 (that is, no separator). 8531 Returns the empty string if <code>n</code> is not positive. 8532 8533 8534 <p> 8535 (Note that it is very easy to exhaust the memory of your machine 8536 with a single call to this function.) 8537 8538 8539 8540 8541 <p> 8542 <hr><h3><a name="pdf-string.reverse"><code>string.reverse (s)</code></a></h3> 8543 Returns a string that is the string <code>s</code> reversed. 8544 8545 8546 8547 8548 <p> 8549 <hr><h3><a name="pdf-string.sub"><code>string.sub (s, i [, j])</code></a></h3> 8550 Returns the substring of <code>s</code> that 8551 starts at <code>i</code> and continues until <code>j</code>; 8552 <code>i</code> and <code>j</code> can be negative. 8553 If <code>j</code> is absent, then it is assumed to be equal to -1 8554 (which is the same as the string length). 8555 In particular, 8556 the call <code>string.sub(s,1,j)</code> returns a prefix of <code>s</code> 8557 with length <code>j</code>, 8558 and <code>string.sub(s, -i)</code> (for a positive <code>i</code>) 8559 returns a suffix of <code>s</code> 8560 with length <code>i</code>. 8561 8562 8563 <p> 8564 If, after the translation of negative indices, 8565 <code>i</code> is less than 1, 8566 it is corrected to 1. 8567 If <code>j</code> is greater than the string length, 8568 it is corrected to that length. 8569 If, after these corrections, 8570 <code>i</code> is greater than <code>j</code>, 8571 the function returns the empty string. 8572 8573 8574 8575 8576 <p> 8577 <hr><h3><a name="pdf-string.unpack"><code>string.unpack (fmt, s [, pos])</code></a></h3> 8578 8579 8580 <p> 8581 Returns the values packed in string <code>s</code> (see <a href="#pdf-string.pack"><code>string.pack</code></a>) 8582 according to the format string <code>fmt</code> (see <a href="#6.4.2">§6.4.2</a>). 8583 An optional <code>pos</code> marks where 8584 to start reading in <code>s</code> (default is 1). 8585 After the read values, 8586 this function also returns the index of the first unread byte in <code>s</code>. 8587 8588 8589 8590 8591 <p> 8592 <hr><h3><a name="pdf-string.upper"><code>string.upper (s)</code></a></h3> 8593 Receives a string and returns a copy of this string with all 8594 lowercase letters changed to uppercase. 8595 All other characters are left unchanged. 8596 The definition of what a lowercase letter is depends on the current locale. 8597 8598 8599 8600 8601 8602 <h3>6.4.1 – <a name="6.4.1">Patterns</a></h3> 8603 8604 <p> 8605 Patterns in Lua are described by regular strings, 8606 which are interpreted as patterns by the pattern-matching functions 8607 <a href="#pdf-string.find"><code>string.find</code></a>, 8608 <a href="#pdf-string.gmatch"><code>string.gmatch</code></a>, 8609 <a href="#pdf-string.gsub"><code>string.gsub</code></a>, 8610 and <a href="#pdf-string.match"><code>string.match</code></a>. 8611 This section describes the syntax and the meaning 8612 (that is, what they match) of these strings. 8613 8614 8615 8616 <h4>Character Class:</h4><p> 8617 A <em>character class</em> is used to represent a set of characters. 8618 The following combinations are allowed in describing a character class: 8619 8620 <ul> 8621 8622 <li><b><em>x</em>: </b> 8623 (where <em>x</em> is not one of the <em>magic characters</em> 8624 <code>^$()%.[]*+-?</code>) 8625 represents the character <em>x</em> itself. 8626 </li> 8627 8628 <li><b><code>.</code>: </b> (a dot) represents all characters.</li> 8629 8630 <li><b><code>%a</code>: </b> represents all letters.</li> 8631 8632 <li><b><code>%c</code>: </b> represents all control characters.</li> 8633 8634 <li><b><code>%d</code>: </b> represents all digits.</li> 8635 8636 <li><b><code>%g</code>: </b> represents all printable characters except space.</li> 8637 8638 <li><b><code>%l</code>: </b> represents all lowercase letters.</li> 8639 8640 <li><b><code>%p</code>: </b> represents all punctuation characters.</li> 8641 8642 <li><b><code>%s</code>: </b> represents all space characters.</li> 8643 8644 <li><b><code>%u</code>: </b> represents all uppercase letters.</li> 8645 8646 <li><b><code>%w</code>: </b> represents all alphanumeric characters.</li> 8647 8648 <li><b><code>%x</code>: </b> represents all hexadecimal digits.</li> 8649 8650 <li><b><code>%<em>x</em></code>: </b> (where <em>x</em> is any non-alphanumeric character) 8651 represents the character <em>x</em>. 8652 This is the standard way to escape the magic characters. 8653 Any non-alphanumeric character 8654 (including all punctuation characters, even the non-magical) 8655 can be preceded by a '<code>%</code>' 8656 when used to represent itself in a pattern. 8657 </li> 8658 8659 <li><b><code>[<em>set</em>]</code>: </b> 8660 represents the class which is the union of all 8661 characters in <em>set</em>. 8662 A range of characters can be specified by 8663 separating the end characters of the range, 8664 in ascending order, with a '<code>-</code>'. 8665 All classes <code>%</code><em>x</em> described above can also be used as 8666 components in <em>set</em>. 8667 All other characters in <em>set</em> represent themselves. 8668 For example, <code>[%w_]</code> (or <code>[_%w]</code>) 8669 represents all alphanumeric characters plus the underscore, 8670 <code>[0-7]</code> represents the octal digits, 8671 and <code>[0-7%l%-]</code> represents the octal digits plus 8672 the lowercase letters plus the '<code>-</code>' character. 8673 8674 8675 <p> 8676 You can put a closing square bracket in a set 8677 by positioning it as the first character in the set. 8678 You can put a hyphen in a set 8679 by positioning it as the first or the last character in the set. 8680 (You can also use an escape for both cases.) 8681 8682 8683 <p> 8684 The interaction between ranges and classes is not defined. 8685 Therefore, patterns like <code>[%a-z]</code> or <code>[a-%%]</code> 8686 have no meaning. 8687 </li> 8688 8689 <li><b><code>[^<em>set</em>]</code>: </b> 8690 represents the complement of <em>set</em>, 8691 where <em>set</em> is interpreted as above. 8692 </li> 8693 8694 </ul><p> 8695 For all classes represented by single letters (<code>%a</code>, <code>%c</code>, etc.), 8696 the corresponding uppercase letter represents the complement of the class. 8697 For instance, <code>%S</code> represents all non-space characters. 8698 8699 8700 <p> 8701 The definitions of letter, space, and other character groups 8702 depend on the current locale. 8703 In particular, the class <code>[a-z]</code> may not be equivalent to <code>%l</code>. 8704 8705 8706 8707 8708 8709 <h4>Pattern Item:</h4><p> 8710 A <em>pattern item</em> can be 8711 8712 <ul> 8713 8714 <li> 8715 a single character class, 8716 which matches any single character in the class; 8717 </li> 8718 8719 <li> 8720 a single character class followed by '<code>*</code>', 8721 which matches zero or more repetitions of characters in the class. 8722 These repetition items will always match the longest possible sequence; 8723 </li> 8724 8725 <li> 8726 a single character class followed by '<code>+</code>', 8727 which matches one or more repetitions of characters in the class. 8728 These repetition items will always match the longest possible sequence; 8729 </li> 8730 8731 <li> 8732 a single character class followed by '<code>-</code>', 8733 which also matches zero or more repetitions of characters in the class. 8734 Unlike '<code>*</code>', 8735 these repetition items will always match the shortest possible sequence; 8736 </li> 8737 8738 <li> 8739 a single character class followed by '<code>?</code>', 8740 which matches zero or one occurrence of a character in the class. 8741 It always matches one occurrence if possible; 8742 </li> 8743 8744 <li> 8745 <code>%<em>n</em></code>, for <em>n</em> between 1 and 9; 8746 such item matches a substring equal to the <em>n</em>-th captured string 8747 (see below); 8748 </li> 8749 8750 <li> 8751 <code>%b<em>xy</em></code>, where <em>x</em> and <em>y</em> are two distinct characters; 8752 such item matches strings that start with <em>x</em>, end with <em>y</em>, 8753 and where the <em>x</em> and <em>y</em> are <em>balanced</em>. 8754 This means that, if one reads the string from left to right, 8755 counting <em>+1</em> for an <em>x</em> and <em>-1</em> for a <em>y</em>, 8756 the ending <em>y</em> is the first <em>y</em> where the count reaches 0. 8757 For instance, the item <code>%b()</code> matches expressions with 8758 balanced parentheses. 8759 </li> 8760 8761 <li> 8762 <code>%f[<em>set</em>]</code>, a <em>frontier pattern</em>; 8763 such item matches an empty string at any position such that 8764 the next character belongs to <em>set</em> 8765 and the previous character does not belong to <em>set</em>. 8766 The set <em>set</em> is interpreted as previously described. 8767 The beginning and the end of the subject are handled as if 8768 they were the character '<code>\0</code>'. 8769 </li> 8770 8771 </ul> 8772 8773 8774 8775 8776 <h4>Pattern:</h4><p> 8777 A <em>pattern</em> is a sequence of pattern items. 8778 A caret '<code>^</code>' at the beginning of a pattern anchors the match at the 8779 beginning of the subject string. 8780 A '<code>$</code>' at the end of a pattern anchors the match at the 8781 end of the subject string. 8782 At other positions, 8783 '<code>^</code>' and '<code>$</code>' have no special meaning and represent themselves. 8784 8785 8786 8787 8788 8789 <h4>Captures:</h4><p> 8790 A pattern can contain sub-patterns enclosed in parentheses; 8791 they describe <em>captures</em>. 8792 When a match succeeds, the substrings of the subject string 8793 that match captures are stored (<em>captured</em>) for future use. 8794 Captures are numbered according to their left parentheses. 8795 For instance, in the pattern <code>"(a*(.)%w(%s*))"</code>, 8796 the part of the string matching <code>"a*(.)%w(%s*)"</code> is 8797 stored as the first capture (and therefore has number 1); 8798 the character matching "<code>.</code>" is captured with number 2, 8799 and the part matching "<code>%s*</code>" has number 3. 8800 8801 8802 <p> 8803 As a special case, the empty capture <code>()</code> captures 8804 the current string position (a number). 8805 For instance, if we apply the pattern <code>"()aa()"</code> on the 8806 string <code>"flaaap"</code>, there will be two captures: 3 and 5. 8807 8808 8809 8810 8811 8812 8813 8814 <h3>6.4.2 – <a name="6.4.2">Format Strings for Pack and Unpack</a></h3> 8815 8816 <p> 8817 The first argument to <a href="#pdf-string.pack"><code>string.pack</code></a>, 8818 <a href="#pdf-string.packsize"><code>string.packsize</code></a>, and <a href="#pdf-string.unpack"><code>string.unpack</code></a> 8819 is a format string, 8820 which describes the layout of the structure being created or read. 8821 8822 8823 <p> 8824 A format string is a sequence of conversion options. 8825 The conversion options are as follows: 8826 8827 <ul> 8828 <li><b><code><</code>: </b>sets little endian</li> 8829 <li><b><code>></code>: </b>sets big endian</li> 8830 <li><b><code>=</code>: </b>sets native endian</li> 8831 <li><b><code>![<em>n</em>]</code>: </b>sets maximum alignment to <code>n</code> 8832 (default is native alignment)</li> 8833 <li><b><code>b</code>: </b>a signed byte (<code>char</code>)</li> 8834 <li><b><code>B</code>: </b>an unsigned byte (<code>char</code>)</li> 8835 <li><b><code>h</code>: </b>a signed <code>short</code> (native size)</li> 8836 <li><b><code>H</code>: </b>an unsigned <code>short</code> (native size)</li> 8837 <li><b><code>l</code>: </b>a signed <code>long</code> (native size)</li> 8838 <li><b><code>L</code>: </b>an unsigned <code>long</code> (native size)</li> 8839 <li><b><code>j</code>: </b>a <code>lua_Integer</code></li> 8840 <li><b><code>J</code>: </b>a <code>lua_Unsigned</code></li> 8841 <li><b><code>T</code>: </b>a <code>size_t</code> (native size)</li> 8842 <li><b><code>i[<em>n</em>]</code>: </b>a signed <code>int</code> with <code>n</code> bytes 8843 (default is native size)</li> 8844 <li><b><code>I[<em>n</em>]</code>: </b>an unsigned <code>int</code> with <code>n</code> bytes 8845 (default is native size)</li> 8846 <li><b><code>f</code>: </b>a <code>float</code> (native size)</li> 8847 <li><b><code>d</code>: </b>a <code>double</code> (native size)</li> 8848 <li><b><code>n</code>: </b>a <code>lua_Number</code></li> 8849 <li><b><code>c<em>n</em></code>: </b>a fixed-sized string with <code>n</code> bytes</li> 8850 <li><b><code>z</code>: </b>a zero-terminated string</li> 8851 <li><b><code>s[<em>n</em>]</code>: </b>a string preceded by its length 8852 coded as an unsigned integer with <code>n</code> bytes 8853 (default is a <code>size_t</code>)</li> 8854 <li><b><code>x</code>: </b>one byte of padding</li> 8855 <li><b><code>X<em>op</em></code>: </b>an empty item that aligns 8856 according to option <code>op</code> 8857 (which is otherwise ignored)</li> 8858 <li><b>'<code> </code>': </b>(empty space) ignored</li> 8859 </ul><p> 8860 (A "<code>[<em>n</em>]</code>" means an optional integral numeral.) 8861 Except for padding, spaces, and configurations 8862 (options "<code>xX <=>!</code>"), 8863 each option corresponds to an argument (in <a href="#pdf-string.pack"><code>string.pack</code></a>) 8864 or a result (in <a href="#pdf-string.unpack"><code>string.unpack</code></a>). 8865 8866 8867 <p> 8868 For options "<code>!<em>n</em></code>", "<code>s<em>n</em></code>", "<code>i<em>n</em></code>", and "<code>I<em>n</em></code>", 8869 <code>n</code> can be any integer between 1 and 16. 8870 All integral options check overflows; 8871 <a href="#pdf-string.pack"><code>string.pack</code></a> checks whether the given value fits in the given size; 8872 <a href="#pdf-string.unpack"><code>string.unpack</code></a> checks whether the read value fits in a Lua integer. 8873 8874 8875 <p> 8876 Any format string starts as if prefixed by "<code>!1=</code>", 8877 that is, 8878 with maximum alignment of 1 (no alignment) 8879 and native endianness. 8880 8881 8882 <p> 8883 Alignment works as follows: 8884 For each option, 8885 the format gets extra padding until the data starts 8886 at an offset that is a multiple of the minimum between the 8887 option size and the maximum alignment; 8888 this minimum must be a power of 2. 8889 Options "<code>c</code>" and "<code>z</code>" are not aligned; 8890 option "<code>s</code>" follows the alignment of its starting integer. 8891 8892 8893 <p> 8894 All padding is filled with zeros by <a href="#pdf-string.pack"><code>string.pack</code></a> 8895 (and ignored by <a href="#pdf-string.unpack"><code>string.unpack</code></a>). 8896 8897 8898 8899 8900 8901 8902 8903 <h2>6.5 – <a name="6.5">UTF-8 Support</a></h2> 8904 8905 <p> 8906 This library provides basic support for UTF-8 encoding. 8907 It provides all its functions inside the table <a name="pdf-utf8"><code>utf8</code></a>. 8908 This library does not provide any support for Unicode other 8909 than the handling of the encoding. 8910 Any operation that needs the meaning of a character, 8911 such as character classification, is outside its scope. 8912 8913 8914 <p> 8915 Unless stated otherwise, 8916 all functions that expect a byte position as a parameter 8917 assume that the given position is either the start of a byte sequence 8918 or one plus the length of the subject string. 8919 As in the string library, 8920 negative indices count from the end of the string. 8921 8922 8923 <p> 8924 <hr><h3><a name="pdf-utf8.char"><code>utf8.char (···)</code></a></h3> 8925 Receives zero or more integers, 8926 converts each one to its corresponding UTF-8 byte sequence 8927 and returns a string with the concatenation of all these sequences. 8928 8929 8930 8931 8932 <p> 8933 <hr><h3><a name="pdf-utf8.charpattern"><code>utf8.charpattern</code></a></h3> 8934 The pattern (a string, not a function) "<code>[\0-\x7F\xC2-\xF4][\x80-\xBF]*</code>" 8935 (see <a href="#6.4.1">§6.4.1</a>), 8936 which matches exactly one UTF-8 byte sequence, 8937 assuming that the subject is a valid UTF-8 string. 8938 8939 8940 8941 8942 <p> 8943 <hr><h3><a name="pdf-utf8.codes"><code>utf8.codes (s)</code></a></h3> 8944 8945 8946 <p> 8947 Returns values so that the construction 8948 8949 <pre> 8950 for p, c in utf8.codes(s) do <em>body</em> end 8951 </pre><p> 8952 will iterate over all characters in string <code>s</code>, 8953 with <code>p</code> being the position (in bytes) and <code>c</code> the code point 8954 of each character. 8955 It raises an error if it meets any invalid byte sequence. 8956 8957 8958 8959 8960 <p> 8961 <hr><h3><a name="pdf-utf8.codepoint"><code>utf8.codepoint (s [, i [, j]])</code></a></h3> 8962 Returns the codepoints (as integers) from all characters in <code>s</code> 8963 that start between byte position <code>i</code> and <code>j</code> (both included). 8964 The default for <code>i</code> is 1 and for <code>j</code> is <code>i</code>. 8965 It raises an error if it meets any invalid byte sequence. 8966 8967 8968 8969 8970 <p> 8971 <hr><h3><a name="pdf-utf8.len"><code>utf8.len (s [, i [, j]])</code></a></h3> 8972 Returns the number of UTF-8 characters in string <code>s</code> 8973 that start between positions <code>i</code> and <code>j</code> (both inclusive). 8974 The default for <code>i</code> is 1 and for <code>j</code> is -1. 8975 If it finds any invalid byte sequence, 8976 returns a false value plus the position of the first invalid byte. 8977 8978 8979 8980 8981 <p> 8982 <hr><h3><a name="pdf-utf8.offset"><code>utf8.offset (s, n [, i])</code></a></h3> 8983 Returns the position (in bytes) where the encoding of the 8984 <code>n</code>-th character of <code>s</code> 8985 (counting from position <code>i</code>) starts. 8986 A negative <code>n</code> gets characters before position <code>i</code>. 8987 The default for <code>i</code> is 1 when <code>n</code> is non-negative 8988 and <code>#s + 1</code> otherwise, 8989 so that <code>utf8.offset(s, -n)</code> gets the offset of the 8990 <code>n</code>-th character from the end of the string. 8991 If the specified character is neither in the subject 8992 nor right after its end, 8993 the function returns <b>nil</b>. 8994 8995 8996 <p> 8997 As a special case, 8998 when <code>n</code> is 0 the function returns the start of the encoding 8999 of the character that contains the <code>i</code>-th byte of <code>s</code>. 9000 9001 9002 <p> 9003 This function assumes that <code>s</code> is a valid UTF-8 string. 9004 9005 9006 9007 9008 9009 9010 9011 <h2>6.6 – <a name="6.6">Table Manipulation</a></h2> 9012 9013 <p> 9014 This library provides generic functions for table manipulation. 9015 It provides all its functions inside the table <a name="pdf-table"><code>table</code></a>. 9016 9017 9018 <p> 9019 Remember that, whenever an operation needs the length of a table, 9020 all caveats about the length operator apply (see <a href="#3.4.7">§3.4.7</a>). 9021 All functions ignore non-numeric keys 9022 in the tables given as arguments. 9023 9024 9025 <p> 9026 <hr><h3><a name="pdf-table.concat"><code>table.concat (list [, sep [, i [, j]]])</code></a></h3> 9027 9028 9029 <p> 9030 Given a list where all elements are strings or numbers, 9031 returns the string <code>list[i]..sep..list[i+1] ··· sep..list[j]</code>. 9032 The default value for <code>sep</code> is the empty string, 9033 the default for <code>i</code> is 1, 9034 and the default for <code>j</code> is <code>#list</code>. 9035 If <code>i</code> is greater than <code>j</code>, returns the empty string. 9036 9037 9038 9039 9040 <p> 9041 <hr><h3><a name="pdf-table.insert"><code>table.insert (list, [pos,] value)</code></a></h3> 9042 9043 9044 <p> 9045 Inserts element <code>value</code> at position <code>pos</code> in <code>list</code>, 9046 shifting up the elements 9047 <code>list[pos], list[pos+1], ···, list[#list]</code>. 9048 The default value for <code>pos</code> is <code>#list+1</code>, 9049 so that a call <code>table.insert(t,x)</code> inserts <code>x</code> at the end 9050 of list <code>t</code>. 9051 9052 9053 9054 9055 <p> 9056 <hr><h3><a name="pdf-table.move"><code>table.move (a1, f, e, t [,a2])</code></a></h3> 9057 9058 9059 <p> 9060 Moves elements from table <code>a1</code> to table <code>a2</code>, 9061 performing the equivalent to the following 9062 multiple assignment: 9063 <code>a2[t],··· = a1[f],···,a1[e]</code>. 9064 The default for <code>a2</code> is <code>a1</code>. 9065 The destination range can overlap with the source range. 9066 The number of elements to be moved must fit in a Lua integer. 9067 9068 9069 <p> 9070 Returns the destination table <code>a2</code>. 9071 9072 9073 9074 9075 <p> 9076 <hr><h3><a name="pdf-table.pack"><code>table.pack (···)</code></a></h3> 9077 9078 9079 <p> 9080 Returns a new table with all arguments stored into keys 1, 2, etc. 9081 and with a field "<code>n</code>" with the total number of arguments. 9082 Note that the resulting table may not be a sequence. 9083 9084 9085 9086 9087 <p> 9088 <hr><h3><a name="pdf-table.remove"><code>table.remove (list [, pos])</code></a></h3> 9089 9090 9091 <p> 9092 Removes from <code>list</code> the element at position <code>pos</code>, 9093 returning the value of the removed element. 9094 When <code>pos</code> is an integer between 1 and <code>#list</code>, 9095 it shifts down the elements 9096 <code>list[pos+1], list[pos+2], ···, list[#list]</code> 9097 and erases element <code>list[#list]</code>; 9098 The index <code>pos</code> can also be 0 when <code>#list</code> is 0, 9099 or <code>#list + 1</code>; 9100 in those cases, the function erases the element <code>list[pos]</code>. 9101 9102 9103 <p> 9104 The default value for <code>pos</code> is <code>#list</code>, 9105 so that a call <code>table.remove(l)</code> removes the last element 9106 of list <code>l</code>. 9107 9108 9109 9110 9111 <p> 9112 <hr><h3><a name="pdf-table.sort"><code>table.sort (list [, comp])</code></a></h3> 9113 9114 9115 <p> 9116 Sorts list elements in a given order, <em>in-place</em>, 9117 from <code>list[1]</code> to <code>list[#list]</code>. 9118 If <code>comp</code> is given, 9119 then it must be a function that receives two list elements 9120 and returns true when the first element must come 9121 before the second in the final order 9122 (so that, after the sort, 9123 <code>i < j</code> implies <code>not comp(list[j],list[i])</code>). 9124 If <code>comp</code> is not given, 9125 then the standard Lua operator <code><</code> is used instead. 9126 9127 9128 <p> 9129 Note that the <code>comp</code> function must define 9130 a strict partial order over the elements in the list; 9131 that is, it must be asymmetric and transitive. 9132 Otherwise, no valid sort may be possible. 9133 9134 9135 <p> 9136 The sort algorithm is not stable: 9137 elements considered equal by the given order 9138 may have their relative positions changed by the sort. 9139 9140 9141 9142 9143 <p> 9144 <hr><h3><a name="pdf-table.unpack"><code>table.unpack (list [, i [, j]])</code></a></h3> 9145 9146 9147 <p> 9148 Returns the elements from the given list. 9149 This function is equivalent to 9150 9151 <pre> 9152 return list[i], list[i+1], ···, list[j] 9153 </pre><p> 9154 By default, <code>i</code> is 1 and <code>j</code> is <code>#list</code>. 9155 9156 9157 9158 9159 9160 9161 9162 <h2>6.7 – <a name="6.7">Mathematical Functions</a></h2> 9163 9164 <p> 9165 This library provides basic mathematical functions. 9166 It provides all its functions and constants inside the table <a name="pdf-math"><code>math</code></a>. 9167 Functions with the annotation "<code>integer/float</code>" give 9168 integer results for integer arguments 9169 and float results for float (or mixed) arguments. 9170 Rounding functions 9171 (<a href="#pdf-math.ceil"><code>math.ceil</code></a>, <a href="#pdf-math.floor"><code>math.floor</code></a>, and <a href="#pdf-math.modf"><code>math.modf</code></a>) 9172 return an integer when the result fits in the range of an integer, 9173 or a float otherwise. 9174 9175 9176 <p> 9177 <hr><h3><a name="pdf-math.abs"><code>math.abs (x)</code></a></h3> 9178 9179 9180 <p> 9181 Returns the absolute value of <code>x</code>. (integer/float) 9182 9183 9184 9185 9186 <p> 9187 <hr><h3><a name="pdf-math.acos"><code>math.acos (x)</code></a></h3> 9188 9189 9190 <p> 9191 Returns the arc cosine of <code>x</code> (in radians). 9192 9193 9194 9195 9196 <p> 9197 <hr><h3><a name="pdf-math.asin"><code>math.asin (x)</code></a></h3> 9198 9199 9200 <p> 9201 Returns the arc sine of <code>x</code> (in radians). 9202 9203 9204 9205 9206 <p> 9207 <hr><h3><a name="pdf-math.atan"><code>math.atan (y [, x])</code></a></h3> 9208 9209 9210 <p> 9211 9212 Returns the arc tangent of <code>y/x</code> (in radians), 9213 but uses the signs of both arguments to find the 9214 quadrant of the result. 9215 (It also handles correctly the case of <code>x</code> being zero.) 9216 9217 9218 <p> 9219 The default value for <code>x</code> is 1, 9220 so that the call <code>math.atan(y)</code> 9221 returns the arc tangent of <code>y</code>. 9222 9223 9224 9225 9226 <p> 9227 <hr><h3><a name="pdf-math.ceil"><code>math.ceil (x)</code></a></h3> 9228 9229 9230 <p> 9231 Returns the smallest integral value larger than or equal to <code>x</code>. 9232 9233 9234 9235 9236 <p> 9237 <hr><h3><a name="pdf-math.cos"><code>math.cos (x)</code></a></h3> 9238 9239 9240 <p> 9241 Returns the cosine of <code>x</code> (assumed to be in radians). 9242 9243 9244 9245 9246 <p> 9247 <hr><h3><a name="pdf-math.deg"><code>math.deg (x)</code></a></h3> 9248 9249 9250 <p> 9251 Converts the angle <code>x</code> from radians to degrees. 9252 9253 9254 9255 9256 <p> 9257 <hr><h3><a name="pdf-math.exp"><code>math.exp (x)</code></a></h3> 9258 9259 9260 <p> 9261 Returns the value <em>e<sup>x</sup></em> 9262 (where <code>e</code> is the base of natural logarithms). 9263 9264 9265 9266 9267 <p> 9268 <hr><h3><a name="pdf-math.floor"><code>math.floor (x)</code></a></h3> 9269 9270 9271 <p> 9272 Returns the largest integral value smaller than or equal to <code>x</code>. 9273 9274 9275 9276 9277 <p> 9278 <hr><h3><a name="pdf-math.fmod"><code>math.fmod (x, y)</code></a></h3> 9279 9280 9281 <p> 9282 Returns the remainder of the division of <code>x</code> by <code>y</code> 9283 that rounds the quotient towards zero. (integer/float) 9284 9285 9286 9287 9288 <p> 9289 <hr><h3><a name="pdf-math.huge"><code>math.huge</code></a></h3> 9290 9291 9292 <p> 9293 The float value <code>HUGE_VAL</code>, 9294 a value larger than any other numeric value. 9295 9296 9297 9298 9299 <p> 9300 <hr><h3><a name="pdf-math.log"><code>math.log (x [, base])</code></a></h3> 9301 9302 9303 <p> 9304 Returns the logarithm of <code>x</code> in the given base. 9305 The default for <code>base</code> is <em>e</em> 9306 (so that the function returns the natural logarithm of <code>x</code>). 9307 9308 9309 9310 9311 <p> 9312 <hr><h3><a name="pdf-math.max"><code>math.max (x, ···)</code></a></h3> 9313 9314 9315 <p> 9316 Returns the argument with the maximum value, 9317 according to the Lua operator <code><</code>. (integer/float) 9318 9319 9320 9321 9322 <p> 9323 <hr><h3><a name="pdf-math.maxinteger"><code>math.maxinteger</code></a></h3> 9324 An integer with the maximum value for an integer. 9325 9326 9327 9328 9329 <p> 9330 <hr><h3><a name="pdf-math.min"><code>math.min (x, ···)</code></a></h3> 9331 9332 9333 <p> 9334 Returns the argument with the minimum value, 9335 according to the Lua operator <code><</code>. (integer/float) 9336 9337 9338 9339 9340 <p> 9341 <hr><h3><a name="pdf-math.mininteger"><code>math.mininteger</code></a></h3> 9342 An integer with the minimum value for an integer. 9343 9344 9345 9346 9347 <p> 9348 <hr><h3><a name="pdf-math.modf"><code>math.modf (x)</code></a></h3> 9349 9350 9351 <p> 9352 Returns the integral part of <code>x</code> and the fractional part of <code>x</code>. 9353 Its second result is always a float. 9354 9355 9356 9357 9358 <p> 9359 <hr><h3><a name="pdf-math.pi"><code>math.pi</code></a></h3> 9360 9361 9362 <p> 9363 The value of <em>π</em>. 9364 9365 9366 9367 9368 <p> 9369 <hr><h3><a name="pdf-math.rad"><code>math.rad (x)</code></a></h3> 9370 9371 9372 <p> 9373 Converts the angle <code>x</code> from degrees to radians. 9374 9375 9376 9377 9378 <p> 9379 <hr><h3><a name="pdf-math.random"><code>math.random ([m [, n]])</code></a></h3> 9380 9381 9382 <p> 9383 When called without arguments, 9384 returns a pseudo-random float with uniform distribution 9385 in the range <em>[0,1)</em>. 9386 When called with two integers <code>m</code> and <code>n</code>, 9387 <code>math.random</code> returns a pseudo-random integer 9388 with uniform distribution in the range <em>[m, n]</em>. 9389 (The value <em>n-m</em> cannot be negative and must fit in a Lua integer.) 9390 The call <code>math.random(n)</code> is equivalent to <code>math.random(1,n)</code>. 9391 9392 9393 <p> 9394 This function is an interface to the underling 9395 pseudo-random generator function provided by C. 9396 9397 9398 9399 9400 <p> 9401 <hr><h3><a name="pdf-math.randomseed"><code>math.randomseed (x)</code></a></h3> 9402 9403 9404 <p> 9405 Sets <code>x</code> as the "seed" 9406 for the pseudo-random generator: 9407 equal seeds produce equal sequences of numbers. 9408 9409 9410 9411 9412 <p> 9413 <hr><h3><a name="pdf-math.sin"><code>math.sin (x)</code></a></h3> 9414 9415 9416 <p> 9417 Returns the sine of <code>x</code> (assumed to be in radians). 9418 9419 9420 9421 9422 <p> 9423 <hr><h3><a name="pdf-math.sqrt"><code>math.sqrt (x)</code></a></h3> 9424 9425 9426 <p> 9427 Returns the square root of <code>x</code>. 9428 (You can also use the expression <code>x^0.5</code> to compute this value.) 9429 9430 9431 9432 9433 <p> 9434 <hr><h3><a name="pdf-math.tan"><code>math.tan (x)</code></a></h3> 9435 9436 9437 <p> 9438 Returns the tangent of <code>x</code> (assumed to be in radians). 9439 9440 9441 9442 9443 <p> 9444 <hr><h3><a name="pdf-math.tointeger"><code>math.tointeger (x)</code></a></h3> 9445 9446 9447 <p> 9448 If the value <code>x</code> is convertible to an integer, 9449 returns that integer. 9450 Otherwise, returns <b>nil</b>. 9451 9452 9453 9454 9455 <p> 9456 <hr><h3><a name="pdf-math.type"><code>math.type (x)</code></a></h3> 9457 9458 9459 <p> 9460 Returns "<code>integer</code>" if <code>x</code> is an integer, 9461 "<code>float</code>" if it is a float, 9462 or <b>nil</b> if <code>x</code> is not a number. 9463 9464 9465 9466 9467 <p> 9468 <hr><h3><a name="pdf-math.ult"><code>math.ult (m, n)</code></a></h3> 9469 9470 9471 <p> 9472 Returns a boolean, 9473 true if and only if integer <code>m</code> is below integer <code>n</code> when 9474 they are compared as unsigned integers. 9475 9476 9477 9478 9479 9480 9481 9482 <h2>6.8 – <a name="6.8">Input and Output Facilities</a></h2> 9483 9484 <p> 9485 The I/O library provides two different styles for file manipulation. 9486 The first one uses implicit file handles; 9487 that is, there are operations to set a default input file and a 9488 default output file, 9489 and all input/output operations are over these default files. 9490 The second style uses explicit file handles. 9491 9492 9493 <p> 9494 When using implicit file handles, 9495 all operations are supplied by table <a name="pdf-io"><code>io</code></a>. 9496 When using explicit file handles, 9497 the operation <a href="#pdf-io.open"><code>io.open</code></a> returns a file handle 9498 and then all operations are supplied as methods of the file handle. 9499 9500 9501 <p> 9502 The table <code>io</code> also provides 9503 three predefined file handles with their usual meanings from C: 9504 <a name="pdf-io.stdin"><code>io.stdin</code></a>, <a name="pdf-io.stdout"><code>io.stdout</code></a>, and <a name="pdf-io.stderr"><code>io.stderr</code></a>. 9505 The I/O library never closes these files. 9506 9507 9508 <p> 9509 Unless otherwise stated, 9510 all I/O functions return <b>nil</b> on failure 9511 (plus an error message as a second result and 9512 a system-dependent error code as a third result) 9513 and some value different from <b>nil</b> on success. 9514 In non-POSIX systems, 9515 the computation of the error message and error code 9516 in case of errors 9517 may be not thread safe, 9518 because they rely on the global C variable <code>errno</code>. 9519 9520 9521 <p> 9522 <hr><h3><a name="pdf-io.close"><code>io.close ([file])</code></a></h3> 9523 9524 9525 <p> 9526 Equivalent to <code>file:close()</code>. 9527 Without a <code>file</code>, closes the default output file. 9528 9529 9530 9531 9532 <p> 9533 <hr><h3><a name="pdf-io.flush"><code>io.flush ()</code></a></h3> 9534 9535 9536 <p> 9537 Equivalent to <code>io.output():flush()</code>. 9538 9539 9540 9541 9542 <p> 9543 <hr><h3><a name="pdf-io.input"><code>io.input ([file])</code></a></h3> 9544 9545 9546 <p> 9547 When called with a file name, it opens the named file (in text mode), 9548 and sets its handle as the default input file. 9549 When called with a file handle, 9550 it simply sets this file handle as the default input file. 9551 When called without arguments, 9552 it returns the current default input file. 9553 9554 9555 <p> 9556 In case of errors this function raises the error, 9557 instead of returning an error code. 9558 9559 9560 9561 9562 <p> 9563 <hr><h3><a name="pdf-io.lines"><code>io.lines ([filename, ···])</code></a></h3> 9564 9565 9566 <p> 9567 Opens the given file name in read mode 9568 and returns an iterator function that 9569 works like <code>file:lines(···)</code> over the opened file. 9570 When the iterator function detects the end of file, 9571 it returns no values (to finish the loop) and automatically closes the file. 9572 9573 9574 <p> 9575 The call <code>io.lines()</code> (with no file name) is equivalent 9576 to <code>io.input():lines("*l")</code>; 9577 that is, it iterates over the lines of the default input file. 9578 In this case, the iterator does not close the file when the loop ends. 9579 9580 9581 <p> 9582 In case of errors this function raises the error, 9583 instead of returning an error code. 9584 9585 9586 9587 9588 <p> 9589 <hr><h3><a name="pdf-io.open"><code>io.open (filename [, mode])</code></a></h3> 9590 9591 9592 <p> 9593 This function opens a file, 9594 in the mode specified in the string <code>mode</code>. 9595 In case of success, 9596 it returns a new file handle. 9597 9598 9599 <p> 9600 The <code>mode</code> string can be any of the following: 9601 9602 <ul> 9603 <li><b>"<code>r</code>": </b> read mode (the default);</li> 9604 <li><b>"<code>w</code>": </b> write mode;</li> 9605 <li><b>"<code>a</code>": </b> append mode;</li> 9606 <li><b>"<code>r+</code>": </b> update mode, all previous data is preserved;</li> 9607 <li><b>"<code>w+</code>": </b> update mode, all previous data is erased;</li> 9608 <li><b>"<code>a+</code>": </b> append update mode, previous data is preserved, 9609 writing is only allowed at the end of file.</li> 9610 </ul><p> 9611 The <code>mode</code> string can also have a '<code>b</code>' at the end, 9612 which is needed in some systems to open the file in binary mode. 9613 9614 9615 9616 9617 <p> 9618 <hr><h3><a name="pdf-io.output"><code>io.output ([file])</code></a></h3> 9619 9620 9621 <p> 9622 Similar to <a href="#pdf-io.input"><code>io.input</code></a>, but operates over the default output file. 9623 9624 9625 9626 9627 <p> 9628 <hr><h3><a name="pdf-io.popen"><code>io.popen (prog [, mode])</code></a></h3> 9629 9630 9631 <p> 9632 This function is system dependent and is not available 9633 on all platforms. 9634 9635 9636 <p> 9637 Starts program <code>prog</code> in a separated process and returns 9638 a file handle that you can use to read data from this program 9639 (if <code>mode</code> is <code>"r"</code>, the default) 9640 or to write data to this program 9641 (if <code>mode</code> is <code>"w"</code>). 9642 9643 9644 9645 9646 <p> 9647 <hr><h3><a name="pdf-io.read"><code>io.read (···)</code></a></h3> 9648 9649 9650 <p> 9651 Equivalent to <code>io.input():read(···)</code>. 9652 9653 9654 9655 9656 <p> 9657 <hr><h3><a name="pdf-io.tmpfile"><code>io.tmpfile ()</code></a></h3> 9658 9659 9660 <p> 9661 In case of success, 9662 returns a handle for a temporary file. 9663 This file is opened in update mode 9664 and it is automatically removed when the program ends. 9665 9666 9667 9668 9669 <p> 9670 <hr><h3><a name="pdf-io.type"><code>io.type (obj)</code></a></h3> 9671 9672 9673 <p> 9674 Checks whether <code>obj</code> is a valid file handle. 9675 Returns the string <code>"file"</code> if <code>obj</code> is an open file handle, 9676 <code>"closed file"</code> if <code>obj</code> is a closed file handle, 9677 or <b>nil</b> if <code>obj</code> is not a file handle. 9678 9679 9680 9681 9682 <p> 9683 <hr><h3><a name="pdf-io.write"><code>io.write (···)</code></a></h3> 9684 9685 9686 <p> 9687 Equivalent to <code>io.output():write(···)</code>. 9688 9689 9690 9691 9692 <p> 9693 <hr><h3><a name="pdf-file:close"><code>file:close ()</code></a></h3> 9694 9695 9696 <p> 9697 Closes <code>file</code>. 9698 Note that files are automatically closed when 9699 their handles are garbage collected, 9700 but that takes an unpredictable amount of time to happen. 9701 9702 9703 <p> 9704 When closing a file handle created with <a href="#pdf-io.popen"><code>io.popen</code></a>, 9705 <a href="#pdf-file:close"><code>file:close</code></a> returns the same values 9706 returned by <a href="#pdf-os.execute"><code>os.execute</code></a>. 9707 9708 9709 9710 9711 <p> 9712 <hr><h3><a name="pdf-file:flush"><code>file:flush ()</code></a></h3> 9713 9714 9715 <p> 9716 Saves any written data to <code>file</code>. 9717 9718 9719 9720 9721 <p> 9722 <hr><h3><a name="pdf-file:lines"><code>file:lines (···)</code></a></h3> 9723 9724 9725 <p> 9726 Returns an iterator function that, 9727 each time it is called, 9728 reads the file according to the given formats. 9729 When no format is given, 9730 uses "<code>l</code>" as a default. 9731 As an example, the construction 9732 9733 <pre> 9734 for c in file:lines(1) do <em>body</em> end 9735 </pre><p> 9736 will iterate over all characters of the file, 9737 starting at the current position. 9738 Unlike <a href="#pdf-io.lines"><code>io.lines</code></a>, this function does not close the file 9739 when the loop ends. 9740 9741 9742 <p> 9743 In case of errors this function raises the error, 9744 instead of returning an error code. 9745 9746 9747 9748 9749 <p> 9750 <hr><h3><a name="pdf-file:read"><code>file:read (···)</code></a></h3> 9751 9752 9753 <p> 9754 Reads the file <code>file</code>, 9755 according to the given formats, which specify what to read. 9756 For each format, 9757 the function returns a string or a number with the characters read, 9758 or <b>nil</b> if it cannot read data with the specified format. 9759 (In this latter case, 9760 the function does not read subsequent formats.) 9761 When called without formats, 9762 it uses a default format that reads the next line 9763 (see below). 9764 9765 9766 <p> 9767 The available formats are 9768 9769 <ul> 9770 9771 <li><b>"<code>n</code>": </b> 9772 reads a numeral and returns it as a float or an integer, 9773 following the lexical conventions of Lua. 9774 (The numeral may have leading spaces and a sign.) 9775 This format always reads the longest input sequence that 9776 is a valid prefix for a numeral; 9777 if that prefix does not form a valid numeral 9778 (e.g., an empty string, "<code>0x</code>", or "<code>3.4e-</code>"), 9779 it is discarded and the function returns <b>nil</b>. 9780 </li> 9781 9782 <li><b>"<code>a</code>": </b> 9783 reads the whole file, starting at the current position. 9784 On end of file, it returns the empty string. 9785 </li> 9786 9787 <li><b>"<code>l</code>": </b> 9788 reads the next line skipping the end of line, 9789 returning <b>nil</b> on end of file. 9790 This is the default format. 9791 </li> 9792 9793 <li><b>"<code>L</code>": </b> 9794 reads the next line keeping the end-of-line character (if present), 9795 returning <b>nil</b> on end of file. 9796 </li> 9797 9798 <li><b><em>number</em>: </b> 9799 reads a string with up to this number of bytes, 9800 returning <b>nil</b> on end of file. 9801 If <code>number</code> is zero, 9802 it reads nothing and returns an empty string, 9803 or <b>nil</b> on end of file. 9804 </li> 9805 9806 </ul><p> 9807 The formats "<code>l</code>" and "<code>L</code>" should be used only for text files. 9808 9809 9810 9811 9812 <p> 9813 <hr><h3><a name="pdf-file:seek"><code>file:seek ([whence [, offset]])</code></a></h3> 9814 9815 9816 <p> 9817 Sets and gets the file position, 9818 measured from the beginning of the file, 9819 to the position given by <code>offset</code> plus a base 9820 specified by the string <code>whence</code>, as follows: 9821 9822 <ul> 9823 <li><b>"<code>set</code>": </b> base is position 0 (beginning of the file);</li> 9824 <li><b>"<code>cur</code>": </b> base is current position;</li> 9825 <li><b>"<code>end</code>": </b> base is end of file;</li> 9826 </ul><p> 9827 In case of success, <code>seek</code> returns the final file position, 9828 measured in bytes from the beginning of the file. 9829 If <code>seek</code> fails, it returns <b>nil</b>, 9830 plus a string describing the error. 9831 9832 9833 <p> 9834 The default value for <code>whence</code> is <code>"cur"</code>, 9835 and for <code>offset</code> is 0. 9836 Therefore, the call <code>file:seek()</code> returns the current 9837 file position, without changing it; 9838 the call <code>file:seek("set")</code> sets the position to the 9839 beginning of the file (and returns 0); 9840 and the call <code>file:seek("end")</code> sets the position to the 9841 end of the file, and returns its size. 9842 9843 9844 9845 9846 <p> 9847 <hr><h3><a name="pdf-file:setvbuf"><code>file:setvbuf (mode [, size])</code></a></h3> 9848 9849 9850 <p> 9851 Sets the buffering mode for an output file. 9852 There are three available modes: 9853 9854 <ul> 9855 9856 <li><b>"<code>no</code>": </b> 9857 no buffering; the result of any output operation appears immediately. 9858 </li> 9859 9860 <li><b>"<code>full</code>": </b> 9861 full buffering; output operation is performed only 9862 when the buffer is full or when 9863 you explicitly <code>flush</code> the file (see <a href="#pdf-io.flush"><code>io.flush</code></a>). 9864 </li> 9865 9866 <li><b>"<code>line</code>": </b> 9867 line buffering; output is buffered until a newline is output 9868 or there is any input from some special files 9869 (such as a terminal device). 9870 </li> 9871 9872 </ul><p> 9873 For the last two cases, <code>size</code> 9874 specifies the size of the buffer, in bytes. 9875 The default is an appropriate size. 9876 9877 9878 9879 9880 <p> 9881 <hr><h3><a name="pdf-file:write"><code>file:write (···)</code></a></h3> 9882 9883 9884 <p> 9885 Writes the value of each of its arguments to <code>file</code>. 9886 The arguments must be strings or numbers. 9887 9888 9889 <p> 9890 In case of success, this function returns <code>file</code>. 9891 Otherwise it returns <b>nil</b> plus a string describing the error. 9892 9893 9894 9895 9896 9897 9898 9899 <h2>6.9 – <a name="6.9">Operating System Facilities</a></h2> 9900 9901 <p> 9902 This library is implemented through table <a name="pdf-os"><code>os</code></a>. 9903 9904 9905 <p> 9906 <hr><h3><a name="pdf-os.clock"><code>os.clock ()</code></a></h3> 9907 9908 9909 <p> 9910 Returns an approximation of the amount in seconds of CPU time 9911 used by the program. 9912 9913 9914 9915 9916 <p> 9917 <hr><h3><a name="pdf-os.date"><code>os.date ([format [, time]])</code></a></h3> 9918 9919 9920 <p> 9921 Returns a string or a table containing date and time, 9922 formatted according to the given string <code>format</code>. 9923 9924 9925 <p> 9926 If the <code>time</code> argument is present, 9927 this is the time to be formatted 9928 (see the <a href="#pdf-os.time"><code>os.time</code></a> function for a description of this value). 9929 Otherwise, <code>date</code> formats the current time. 9930 9931 9932 <p> 9933 If <code>format</code> starts with '<code>!</code>', 9934 then the date is formatted in Coordinated Universal Time. 9935 After this optional character, 9936 if <code>format</code> is the string "<code>*t</code>", 9937 then <code>date</code> returns a table with the following fields: 9938 <code>year</code>, <code>month</code> (1–12), <code>day</code> (1–31), 9939 <code>hour</code> (0–23), <code>min</code> (0–59), <code>sec</code> (0–61), 9940 <code>wday</code> (weekday, 1–7, Sunday is 1), 9941 <code>yday</code> (day of the year, 1–366), 9942 and <code>isdst</code> (daylight saving flag, a boolean). 9943 This last field may be absent 9944 if the information is not available. 9945 9946 9947 <p> 9948 If <code>format</code> is not "<code>*t</code>", 9949 then <code>date</code> returns the date as a string, 9950 formatted according to the same rules as the ISO C function <code>strftime</code>. 9951 9952 9953 <p> 9954 When called without arguments, 9955 <code>date</code> returns a reasonable date and time representation that depends on 9956 the host system and on the current locale. 9957 (More specifically, <code>os.date()</code> is equivalent to <code>os.date("%c")</code>.) 9958 9959 9960 <p> 9961 In non-POSIX systems, 9962 this function may be not thread safe 9963 because of its reliance on C function <code>gmtime</code> and C function <code>localtime</code>. 9964 9965 9966 9967 9968 <p> 9969 <hr><h3><a name="pdf-os.difftime"><code>os.difftime (t2, t1)</code></a></h3> 9970 9971 9972 <p> 9973 Returns the difference, in seconds, 9974 from time <code>t1</code> to time <code>t2</code> 9975 (where the times are values returned by <a href="#pdf-os.time"><code>os.time</code></a>). 9976 In POSIX, Windows, and some other systems, 9977 this value is exactly <code>t2</code><em>-</em><code>t1</code>. 9978 9979 9980 9981 9982 <p> 9983 <hr><h3><a name="pdf-os.execute"><code>os.execute ([command])</code></a></h3> 9984 9985 9986 <p> 9987 This function is equivalent to the ISO C function <code>system</code>. 9988 It passes <code>command</code> to be executed by an operating system shell. 9989 Its first result is <b>true</b> 9990 if the command terminated successfully, 9991 or <b>nil</b> otherwise. 9992 After this first result 9993 the function returns a string plus a number, 9994 as follows: 9995 9996 <ul> 9997 9998 <li><b>"<code>exit</code>": </b> 9999 the command terminated normally; 10000 the following number is the exit status of the command. 10001 </li> 10002 10003 <li><b>"<code>signal</code>": </b> 10004 the command was terminated by a signal; 10005 the following number is the signal that terminated the command. 10006 </li> 10007 10008 </ul> 10009 10010 <p> 10011 When called without a <code>command</code>, 10012 <code>os.execute</code> returns a boolean that is true if a shell is available. 10013 10014 10015 10016 10017 <p> 10018 <hr><h3><a name="pdf-os.exit"><code>os.exit ([code [, close]])</code></a></h3> 10019 10020 10021 <p> 10022 Calls the ISO C function <code>exit</code> to terminate the host program. 10023 If <code>code</code> is <b>true</b>, 10024 the returned status is <code>EXIT_SUCCESS</code>; 10025 if <code>code</code> is <b>false</b>, 10026 the returned status is <code>EXIT_FAILURE</code>; 10027 if <code>code</code> is a number, 10028 the returned status is this number. 10029 The default value for <code>code</code> is <b>true</b>. 10030 10031 10032 <p> 10033 If the optional second argument <code>close</code> is true, 10034 closes the Lua state before exiting. 10035 10036 10037 10038 10039 <p> 10040 <hr><h3><a name="pdf-os.getenv"><code>os.getenv (varname)</code></a></h3> 10041 10042 10043 <p> 10044 Returns the value of the process environment variable <code>varname</code>, 10045 or <b>nil</b> if the variable is not defined. 10046 10047 10048 10049 10050 <p> 10051 <hr><h3><a name="pdf-os.remove"><code>os.remove (filename)</code></a></h3> 10052 10053 10054 <p> 10055 Deletes the file (or empty directory, on POSIX systems) 10056 with the given name. 10057 If this function fails, it returns <b>nil</b>, 10058 plus a string describing the error and the error code. 10059 Otherwise, it returns true. 10060 10061 10062 10063 10064 <p> 10065 <hr><h3><a name="pdf-os.rename"><code>os.rename (oldname, newname)</code></a></h3> 10066 10067 10068 <p> 10069 Renames the file or directory named <code>oldname</code> to <code>newname</code>. 10070 If this function fails, it returns <b>nil</b>, 10071 plus a string describing the error and the error code. 10072 Otherwise, it returns true. 10073 10074 10075 10076 10077 <p> 10078 <hr><h3><a name="pdf-os.setlocale"><code>os.setlocale (locale [, category])</code></a></h3> 10079 10080 10081 <p> 10082 Sets the current locale of the program. 10083 <code>locale</code> is a system-dependent string specifying a locale; 10084 <code>category</code> is an optional string describing which category to change: 10085 <code>"all"</code>, <code>"collate"</code>, <code>"ctype"</code>, 10086 <code>"monetary"</code>, <code>"numeric"</code>, or <code>"time"</code>; 10087 the default category is <code>"all"</code>. 10088 The function returns the name of the new locale, 10089 or <b>nil</b> if the request cannot be honored. 10090 10091 10092 <p> 10093 If <code>locale</code> is the empty string, 10094 the current locale is set to an implementation-defined native locale. 10095 If <code>locale</code> is the string "<code>C</code>", 10096 the current locale is set to the standard C locale. 10097 10098 10099 <p> 10100 When called with <b>nil</b> as the first argument, 10101 this function only returns the name of the current locale 10102 for the given category. 10103 10104 10105 <p> 10106 This function may be not thread safe 10107 because of its reliance on C function <code>setlocale</code>. 10108 10109 10110 10111 10112 <p> 10113 <hr><h3><a name="pdf-os.time"><code>os.time ([table])</code></a></h3> 10114 10115 10116 <p> 10117 Returns the current time when called without arguments, 10118 or a time representing the local date and time specified by the given table. 10119 This table must have fields <code>year</code>, <code>month</code>, and <code>day</code>, 10120 and may have fields 10121 <code>hour</code> (default is 12), 10122 <code>min</code> (default is 0), 10123 <code>sec</code> (default is 0), 10124 and <code>isdst</code> (default is <b>nil</b>). 10125 Other fields are ignored. 10126 For a description of these fields, see the <a href="#pdf-os.date"><code>os.date</code></a> function. 10127 10128 10129 <p> 10130 The values in these fields do not need to be inside their valid ranges. 10131 For instance, if <code>sec</code> is -10, 10132 it means -10 seconds from the time specified by the other fields; 10133 if <code>hour</code> is 1000, 10134 it means +1000 hours from the time specified by the other fields. 10135 10136 10137 <p> 10138 The returned value is a number, whose meaning depends on your system. 10139 In POSIX, Windows, and some other systems, 10140 this number counts the number 10141 of seconds since some given start time (the "epoch"). 10142 In other systems, the meaning is not specified, 10143 and the number returned by <code>time</code> can be used only as an argument to 10144 <a href="#pdf-os.date"><code>os.date</code></a> and <a href="#pdf-os.difftime"><code>os.difftime</code></a>. 10145 10146 10147 10148 10149 <p> 10150 <hr><h3><a name="pdf-os.tmpname"><code>os.tmpname ()</code></a></h3> 10151 10152 10153 <p> 10154 Returns a string with a file name that can 10155 be used for a temporary file. 10156 The file must be explicitly opened before its use 10157 and explicitly removed when no longer needed. 10158 10159 10160 <p> 10161 In POSIX systems, 10162 this function also creates a file with that name, 10163 to avoid security risks. 10164 (Someone else might create the file with wrong permissions 10165 in the time between getting the name and creating the file.) 10166 You still have to open the file to use it 10167 and to remove it (even if you do not use it). 10168 10169 10170 <p> 10171 When possible, 10172 you may prefer to use <a href="#pdf-io.tmpfile"><code>io.tmpfile</code></a>, 10173 which automatically removes the file when the program ends. 10174 10175 10176 10177 10178 10179 10180 10181 <h2>6.10 – <a name="6.10">The Debug Library</a></h2> 10182 10183 <p> 10184 This library provides 10185 the functionality of the debug interface (<a href="#4.9">§4.9</a>) to Lua programs. 10186 You should exert care when using this library. 10187 Several of its functions 10188 violate basic assumptions about Lua code 10189 (e.g., that variables local to a function 10190 cannot be accessed from outside; 10191 that userdata metatables cannot be changed by Lua code; 10192 that Lua programs do not crash) 10193 and therefore can compromise otherwise secure code. 10194 Moreover, some functions in this library may be slow. 10195 10196 10197 <p> 10198 All functions in this library are provided 10199 inside the <a name="pdf-debug"><code>debug</code></a> table. 10200 All functions that operate over a thread 10201 have an optional first argument which is the 10202 thread to operate over. 10203 The default is always the current thread. 10204 10205 10206 <p> 10207 <hr><h3><a name="pdf-debug.debug"><code>debug.debug ()</code></a></h3> 10208 10209 10210 <p> 10211 Enters an interactive mode with the user, 10212 running each string that the user enters. 10213 Using simple commands and other debug facilities, 10214 the user can inspect global and local variables, 10215 change their values, evaluate expressions, and so on. 10216 A line containing only the word <code>cont</code> finishes this function, 10217 so that the caller continues its execution. 10218 10219 10220 <p> 10221 Note that commands for <code>debug.debug</code> are not lexically nested 10222 within any function and so have no direct access to local variables. 10223 10224 10225 10226 10227 <p> 10228 <hr><h3><a name="pdf-debug.gethook"><code>debug.gethook ([thread])</code></a></h3> 10229 10230 10231 <p> 10232 Returns the current hook settings of the thread, as three values: 10233 the current hook function, the current hook mask, 10234 and the current hook count 10235 (as set by the <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> function). 10236 10237 10238 10239 10240 <p> 10241 <hr><h3><a name="pdf-debug.getinfo"><code>debug.getinfo ([thread,] f [, what])</code></a></h3> 10242 10243 10244 <p> 10245 Returns a table with information about a function. 10246 You can give the function directly 10247 or you can give a number as the value of <code>f</code>, 10248 which means the function running at level <code>f</code> of the call stack 10249 of the given thread: 10250 level 0 is the current function (<code>getinfo</code> itself); 10251 level 1 is the function that called <code>getinfo</code> 10252 (except for tail calls, which do not count on the stack); 10253 and so on. 10254 If <code>f</code> is a number larger than the number of active functions, 10255 then <code>getinfo</code> returns <b>nil</b>. 10256 10257 10258 <p> 10259 The returned table can contain all the fields returned by <a href="#lua_getinfo"><code>lua_getinfo</code></a>, 10260 with the string <code>what</code> describing which fields to fill in. 10261 The default for <code>what</code> is to get all information available, 10262 except the table of valid lines. 10263 If present, 10264 the option '<code>f</code>' 10265 adds a field named <code>func</code> with the function itself. 10266 If present, 10267 the option '<code>L</code>' 10268 adds a field named <code>activelines</code> with the table of 10269 valid lines. 10270 10271 10272 <p> 10273 For instance, the expression <code>debug.getinfo(1,"n").name</code> returns 10274 a name for the current function, 10275 if a reasonable name can be found, 10276 and the expression <code>debug.getinfo(print)</code> 10277 returns a table with all available information 10278 about the <a href="#pdf-print"><code>print</code></a> function. 10279 10280 10281 10282 10283 <p> 10284 <hr><h3><a name="pdf-debug.getlocal"><code>debug.getlocal ([thread,] f, local)</code></a></h3> 10285 10286 10287 <p> 10288 This function returns the name and the value of the local variable 10289 with index <code>local</code> of the function at level <code>f</code> of the stack. 10290 This function accesses not only explicit local variables, 10291 but also parameters, temporaries, etc. 10292 10293 10294 <p> 10295 The first parameter or local variable has index 1, and so on, 10296 following the order that they are declared in the code, 10297 counting only the variables that are active 10298 in the current scope of the function. 10299 Negative indices refer to vararg arguments; 10300 -1 is the first vararg argument. 10301 The function returns <b>nil</b> if there is no variable with the given index, 10302 and raises an error when called with a level out of range. 10303 (You can call <a href="#pdf-debug.getinfo"><code>debug.getinfo</code></a> to check whether the level is valid.) 10304 10305 10306 <p> 10307 Variable names starting with '<code>(</code>' (open parenthesis) 10308 represent variables with no known names 10309 (internal variables such as loop control variables, 10310 and variables from chunks saved without debug information). 10311 10312 10313 <p> 10314 The parameter <code>f</code> may also be a function. 10315 In that case, <code>getlocal</code> returns only the name of function parameters. 10316 10317 10318 10319 10320 <p> 10321 <hr><h3><a name="pdf-debug.getmetatable"><code>debug.getmetatable (value)</code></a></h3> 10322 10323 10324 <p> 10325 Returns the metatable of the given <code>value</code> 10326 or <b>nil</b> if it does not have a metatable. 10327 10328 10329 10330 10331 <p> 10332 <hr><h3><a name="pdf-debug.getregistry"><code>debug.getregistry ()</code></a></h3> 10333 10334 10335 <p> 10336 Returns the registry table (see <a href="#4.5">§4.5</a>). 10337 10338 10339 10340 10341 <p> 10342 <hr><h3><a name="pdf-debug.getupvalue"><code>debug.getupvalue (f, up)</code></a></h3> 10343 10344 10345 <p> 10346 This function returns the name and the value of the upvalue 10347 with index <code>up</code> of the function <code>f</code>. 10348 The function returns <b>nil</b> if there is no upvalue with the given index. 10349 10350 10351 <p> 10352 Variable names starting with '<code>(</code>' (open parenthesis) 10353 represent variables with no known names 10354 (variables from chunks saved without debug information). 10355 10356 10357 10358 10359 <p> 10360 <hr><h3><a name="pdf-debug.getuservalue"><code>debug.getuservalue (u)</code></a></h3> 10361 10362 10363 <p> 10364 Returns the Lua value associated to <code>u</code>. 10365 If <code>u</code> is not a full userdata, 10366 returns <b>nil</b>. 10367 10368 10369 10370 10371 <p> 10372 <hr><h3><a name="pdf-debug.sethook"><code>debug.sethook ([thread,] hook, mask [, count])</code></a></h3> 10373 10374 10375 <p> 10376 Sets the given function as a hook. 10377 The string <code>mask</code> and the number <code>count</code> describe 10378 when the hook will be called. 10379 The string mask may have any combination of the following characters, 10380 with the given meaning: 10381 10382 <ul> 10383 <li><b>'<code>c</code>': </b> the hook is called every time Lua calls a function;</li> 10384 <li><b>'<code>r</code>': </b> the hook is called every time Lua returns from a function;</li> 10385 <li><b>'<code>l</code>': </b> the hook is called every time Lua enters a new line of code.</li> 10386 </ul><p> 10387 Moreover, 10388 with a <code>count</code> different from zero, 10389 the hook is called also after every <code>count</code> instructions. 10390 10391 10392 <p> 10393 When called without arguments, 10394 <a href="#pdf-debug.sethook"><code>debug.sethook</code></a> turns off the hook. 10395 10396 10397 <p> 10398 When the hook is called, its first argument is a string 10399 describing the event that has triggered its call: 10400 <code>"call"</code> (or <code>"tail call"</code>), 10401 <code>"return"</code>, 10402 <code>"line"</code>, and <code>"count"</code>. 10403 For line events, 10404 the hook also gets the new line number as its second parameter. 10405 Inside a hook, 10406 you can call <code>getinfo</code> with level 2 to get more information about 10407 the running function 10408 (level 0 is the <code>getinfo</code> function, 10409 and level 1 is the hook function). 10410 10411 10412 10413 10414 <p> 10415 <hr><h3><a name="pdf-debug.setlocal"><code>debug.setlocal ([thread,] level, local, value)</code></a></h3> 10416 10417 10418 <p> 10419 This function assigns the value <code>value</code> to the local variable 10420 with index <code>local</code> of the function at level <code>level</code> of the stack. 10421 The function returns <b>nil</b> if there is no local 10422 variable with the given index, 10423 and raises an error when called with a <code>level</code> out of range. 10424 (You can call <code>getinfo</code> to check whether the level is valid.) 10425 Otherwise, it returns the name of the local variable. 10426 10427 10428 <p> 10429 See <a href="#pdf-debug.getlocal"><code>debug.getlocal</code></a> for more information about 10430 variable indices and names. 10431 10432 10433 10434 10435 <p> 10436 <hr><h3><a name="pdf-debug.setmetatable"><code>debug.setmetatable (value, table)</code></a></h3> 10437 10438 10439 <p> 10440 Sets the metatable for the given <code>value</code> to the given <code>table</code> 10441 (which can be <b>nil</b>). 10442 Returns <code>value</code>. 10443 10444 10445 10446 10447 <p> 10448 <hr><h3><a name="pdf-debug.setupvalue"><code>debug.setupvalue (f, up, value)</code></a></h3> 10449 10450 10451 <p> 10452 This function assigns the value <code>value</code> to the upvalue 10453 with index <code>up</code> of the function <code>f</code>. 10454 The function returns <b>nil</b> if there is no upvalue 10455 with the given index. 10456 Otherwise, it returns the name of the upvalue. 10457 10458 10459 10460 10461 <p> 10462 <hr><h3><a name="pdf-debug.setuservalue"><code>debug.setuservalue (udata, value)</code></a></h3> 10463 10464 10465 <p> 10466 Sets the given <code>value</code> as 10467 the Lua value associated to the given <code>udata</code>. 10468 <code>udata</code> must be a full userdata. 10469 10470 10471 <p> 10472 Returns <code>udata</code>. 10473 10474 10475 10476 10477 <p> 10478 <hr><h3><a name="pdf-debug.traceback"><code>debug.traceback ([thread,] [message [, level]])</code></a></h3> 10479 10480 10481 <p> 10482 If <code>message</code> is present but is neither a string nor <b>nil</b>, 10483 this function returns <code>message</code> without further processing. 10484 Otherwise, 10485 it returns a string with a traceback of the call stack. 10486 The optional <code>message</code> string is appended 10487 at the beginning of the traceback. 10488 An optional <code>level</code> number tells at which level 10489 to start the traceback 10490 (default is 1, the function calling <code>traceback</code>). 10491 10492 10493 10494 10495 <p> 10496 <hr><h3><a name="pdf-debug.upvalueid"><code>debug.upvalueid (f, n)</code></a></h3> 10497 10498 10499 <p> 10500 Returns a unique identifier (as a light userdata) 10501 for the upvalue numbered <code>n</code> 10502 from the given function. 10503 10504 10505 <p> 10506 These unique identifiers allow a program to check whether different 10507 closures share upvalues. 10508 Lua closures that share an upvalue 10509 (that is, that access a same external local variable) 10510 will return identical ids for those upvalue indices. 10511 10512 10513 10514 10515 <p> 10516 <hr><h3><a name="pdf-debug.upvaluejoin"><code>debug.upvaluejoin (f1, n1, f2, n2)</code></a></h3> 10517 10518 10519 <p> 10520 Make the <code>n1</code>-th upvalue of the Lua closure <code>f1</code> 10521 refer to the <code>n2</code>-th upvalue of the Lua closure <code>f2</code>. 10522 10523 10524 10525 10526 10527 10528 10529 <h1>7 – <a name="7">Lua Standalone</a></h1> 10530 10531 <p> 10532 Although Lua has been designed as an extension language, 10533 to be embedded in a host C program, 10534 it is also frequently used as a standalone language. 10535 An interpreter for Lua as a standalone language, 10536 called simply <code>lua</code>, 10537 is provided with the standard distribution. 10538 The standalone interpreter includes 10539 all standard libraries, including the debug library. 10540 Its usage is: 10541 10542 <pre> 10543 lua [options] [script [args]] 10544 </pre><p> 10545 The options are: 10546 10547 <ul> 10548 <li><b><code>-e <em>stat</em></code>: </b> executes string <em>stat</em>;</li> 10549 <li><b><code>-l <em>mod</em></code>: </b> "requires" <em>mod</em> and assigns the 10550 result to global @<em>mod</em>;</li> 10551 <li><b><code>-i</code>: </b> enters interactive mode after running <em>script</em>;</li> 10552 <li><b><code>-v</code>: </b> prints version information;</li> 10553 <li><b><code>-E</code>: </b> ignores environment variables;</li> 10554 <li><b><code>--</code>: </b> stops handling options;</li> 10555 <li><b><code>-</code>: </b> executes <code>stdin</code> as a file and stops handling options.</li> 10556 </ul><p> 10557 After handling its options, <code>lua</code> runs the given <em>script</em>. 10558 When called without arguments, 10559 <code>lua</code> behaves as <code>lua -v -i</code> 10560 when the standard input (<code>stdin</code>) is a terminal, 10561 and as <code>lua -</code> otherwise. 10562 10563 10564 <p> 10565 When called without option <code>-E</code>, 10566 the interpreter checks for an environment variable <a name="pdf-LUA_INIT_5_3"><code>LUA_INIT_5_3</code></a> 10567 (or <a name="pdf-LUA_INIT"><code>LUA_INIT</code></a> if the versioned name is not defined) 10568 before running any argument. 10569 If the variable content has the format <code>@<em>filename</em></code>, 10570 then <code>lua</code> executes the file. 10571 Otherwise, <code>lua</code> executes the string itself. 10572 10573 10574 <p> 10575 When called with option <code>-E</code>, 10576 besides ignoring <code>LUA_INIT</code>, 10577 Lua also ignores 10578 the values of <code>LUA_PATH</code> and <code>LUA_CPATH</code>, 10579 setting the values of 10580 <a href="#pdf-package.path"><code>package.path</code></a> and <a href="#pdf-package.cpath"><code>package.cpath</code></a> 10581 with the default paths defined in <code>luaconf.h</code>. 10582 10583 10584 <p> 10585 All options are handled in order, except <code>-i</code> and <code>-E</code>. 10586 For instance, an invocation like 10587 10588 <pre> 10589 $ lua -e'a=1' -e 'print(a)' script.lua 10590 </pre><p> 10591 will first set <code>a</code> to 1, then print the value of <code>a</code>, 10592 and finally run the file <code>script.lua</code> with no arguments. 10593 (Here <code>$</code> is the shell prompt. Your prompt may be different.) 10594 10595 10596 <p> 10597 Before running any code, 10598 <code>lua</code> collects all command-line arguments 10599 in a global table called <code>arg</code>. 10600 The script name goes to index 0, 10601 the first argument after the script name goes to index 1, 10602 and so on. 10603 Any arguments before the script name 10604 (that is, the interpreter name plus its options) 10605 go to negative indices. 10606 For instance, in the call 10607 10608 <pre> 10609 $ lua -la b.lua t1 t2 10610 </pre><p> 10611 the table is like this: 10612 10613 <pre> 10614 arg = { [-2] = "lua", [-1] = "-la", 10615 [0] = "b.lua", 10616 [1] = "t1", [2] = "t2" } 10617 </pre><p> 10618 If there is no script in the call, 10619 the interpreter name goes to index 0, 10620 followed by the other arguments. 10621 For instance, the call 10622 10623 <pre> 10624 $ lua -e "print(arg[1])" 10625 </pre><p> 10626 will print "<code>-e</code>". 10627 If there is a script, 10628 the script is called with arguments 10629 <code>arg[1]</code>, ···, <code>arg[#arg]</code>. 10630 (Like all chunks in Lua, 10631 the script is compiled as a vararg function.) 10632 10633 10634 <p> 10635 In interactive mode, 10636 Lua repeatedly prompts and waits for a line. 10637 After reading a line, 10638 Lua first try to interpret the line as an expression. 10639 If it succeeds, it prints its value. 10640 Otherwise, it interprets the line as a statement. 10641 If you write an incomplete statement, 10642 the interpreter waits for its completion 10643 by issuing a different prompt. 10644 10645 10646 <p> 10647 If the global variable <a name="pdf-_PROMPT"><code>_PROMPT</code></a> contains a string, 10648 then its value is used as the prompt. 10649 Similarly, if the global variable <a name="pdf-_PROMPT2"><code>_PROMPT2</code></a> contains a string, 10650 its value is used as the secondary prompt 10651 (issued during incomplete statements). 10652 10653 10654 <p> 10655 In case of unprotected errors in the script, 10656 the interpreter reports the error to the standard error stream. 10657 If the error object is not a string but 10658 has a metamethod <code>__tostring</code>, 10659 the interpreter calls this metamethod to produce the final message. 10660 Otherwise, the interpreter converts the error object to a string 10661 and adds a stack traceback to it. 10662 10663 10664 <p> 10665 When finishing normally, 10666 the interpreter closes its main Lua state 10667 (see <a href="#lua_close"><code>lua_close</code></a>). 10668 The script can avoid this step by 10669 calling <a href="#pdf-os.exit"><code>os.exit</code></a> to terminate. 10670 10671 10672 <p> 10673 To allow the use of Lua as a 10674 script interpreter in Unix systems, 10675 the standalone interpreter skips 10676 the first line of a chunk if it starts with <code>#</code>. 10677 Therefore, Lua scripts can be made into executable programs 10678 by using <code>chmod +x</code> and the <code>#!</code> form, 10679 as in 10680 10681 <pre> 10682 #!/usr/local/bin/lua 10683 </pre><p> 10684 (Of course, 10685 the location of the Lua interpreter may be different in your machine. 10686 If <code>lua</code> is in your <code>PATH</code>, 10687 then 10688 10689 <pre> 10690 #!/usr/bin/env lua 10691 </pre><p> 10692 is a more portable solution.) 10693 10694 10695 10696 <h1>8 – <a name="8">Incompatibilities with the Previous Version</a></h1> 10697 10698 <p> 10699 Here we list the incompatibilities that you may find when moving a program 10700 from Lua 5.2 to Lua 5.3. 10701 You can avoid some incompatibilities by compiling Lua with 10702 appropriate options (see file <code>luaconf.h</code>). 10703 However, 10704 all these compatibility options will be removed in the future. 10705 10706 10707 <p> 10708 Lua versions can always change the C API in ways that 10709 do not imply source-code changes in a program, 10710 such as the numeric values for constants 10711 or the implementation of functions as macros. 10712 Therefore, 10713 you should not assume that binaries are compatible between 10714 different Lua versions. 10715 Always recompile clients of the Lua API when 10716 using a new version. 10717 10718 10719 <p> 10720 Similarly, Lua versions can always change the internal representation 10721 of precompiled chunks; 10722 precompiled chunks are not compatible between different Lua versions. 10723 10724 10725 <p> 10726 The standard paths in the official distribution may 10727 change between versions. 10728 10729 10730 10731 <h2>8.1 – <a name="8.1">Changes in the Language</a></h2> 10732 <ul> 10733 10734 <li> 10735 The main difference between Lua 5.2 and Lua 5.3 is the 10736 introduction of an integer subtype for numbers. 10737 Although this change should not affect "normal" computations, 10738 some computations 10739 (mainly those that involve some kind of overflow) 10740 can give different results. 10741 10742 10743 <p> 10744 You can fix these differences by forcing a number to be a float 10745 (in Lua 5.2 all numbers were float), 10746 in particular writing constants with an ending <code>.0</code> 10747 or using <code>x = x + 0.0</code> to convert a variable. 10748 (This recommendation is only for a quick fix 10749 for an occasional incompatibility; 10750 it is not a general guideline for good programming. 10751 For good programming, 10752 use floats where you need floats 10753 and integers where you need integers.) 10754 </li> 10755 10756 <li> 10757 The conversion of a float to a string now adds a <code>.0</code> suffix 10758 to the result if it looks like an integer. 10759 (For instance, the float 2.0 will be printed as <code>2.0</code>, 10760 not as <code>2</code>.) 10761 You should always use an explicit format 10762 when you need a specific format for numbers. 10763 10764 10765 <p> 10766 (Formally this is not an incompatibility, 10767 because Lua does not specify how numbers are formatted as strings, 10768 but some programs assumed a specific format.) 10769 </li> 10770 10771 <li> 10772 The generational mode for the garbage collector was removed. 10773 (It was an experimental feature in Lua 5.2.) 10774 </li> 10775 10776 </ul> 10777 10778 10779 10780 10781 <h2>8.2 – <a name="8.2">Changes in the Libraries</a></h2> 10782 <ul> 10783 10784 <li> 10785 The <code>bit32</code> library has been deprecated. 10786 It is easy to require a compatible external library or, 10787 better yet, to replace its functions with appropriate bitwise operations. 10788 (Keep in mind that <code>bit32</code> operates on 32-bit integers, 10789 while the bitwise operators in Lua 5.3 operate on Lua integers, 10790 which by default have 64 bits.) 10791 </li> 10792 10793 <li> 10794 The Table library now respects metamethods 10795 for setting and getting elements. 10796 </li> 10797 10798 <li> 10799 The <a href="#pdf-ipairs"><code>ipairs</code></a> iterator now respects metamethods and 10800 its <code>__ipairs</code> metamethod has been deprecated. 10801 </li> 10802 10803 <li> 10804 Option names in <a href="#pdf-io.read"><code>io.read</code></a> do not have a starting '<code>*</code>' anymore. 10805 For compatibility, Lua will continue to accept (and ignore) this character. 10806 </li> 10807 10808 <li> 10809 The following functions were deprecated in the mathematical library: 10810 <code>atan2</code>, <code>cosh</code>, <code>sinh</code>, <code>tanh</code>, <code>pow</code>, 10811 <code>frexp</code>, and <code>ldexp</code>. 10812 You can replace <code>math.pow(x,y)</code> with <code>x^y</code>; 10813 you can replace <code>math.atan2</code> with <code>math.atan</code>, 10814 which now accepts one or two arguments; 10815 you can replace <code>math.ldexp(x,exp)</code> with <code>x * 2.0^exp</code>. 10816 For the other operations, 10817 you can either use an external library or 10818 implement them in Lua. 10819 </li> 10820 10821 <li> 10822 The searcher for C loaders used by <a href="#pdf-require"><code>require</code></a> 10823 changed the way it handles versioned names. 10824 Now, the version should come after the module name 10825 (as is usual in most other tools). 10826 For compatibility, that searcher still tries the old format 10827 if it cannot find an open function according to the new style. 10828 (Lua 5.2 already worked that way, 10829 but it did not document the change.) 10830 </li> 10831 10832 <li> 10833 The call <code>collectgarbage("count")</code> now returns only one result. 10834 (You can compute that second result from the fractional part 10835 of the first result.) 10836 </li> 10837 10838 </ul> 10839 10840 10841 10842 10843 <h2>8.3 – <a name="8.3">Changes in the API</a></h2> 10844 10845 10846 <ul> 10847 10848 <li> 10849 Continuation functions now receive as arguments what they needed 10850 to get through <code>lua_getctx</code>, 10851 so <code>lua_getctx</code> has been removed. 10852 Adapt your code accordingly. 10853 </li> 10854 10855 <li> 10856 Function <a href="#lua_dump"><code>lua_dump</code></a> has an extra parameter, <code>strip</code>. 10857 Use 0 as the value of this parameter to get the old behavior. 10858 </li> 10859 10860 <li> 10861 Functions to inject/project unsigned integers 10862 (<code>lua_pushunsigned</code>, <code>lua_tounsigned</code>, <code>lua_tounsignedx</code>, 10863 <code>luaL_checkunsigned</code>, <code>luaL_optunsigned</code>) 10864 were deprecated. 10865 Use their signed equivalents with a type cast. 10866 </li> 10867 10868 <li> 10869 Macros to project non-default integer types 10870 (<code>luaL_checkint</code>, <code>luaL_optint</code>, <code>luaL_checklong</code>, <code>luaL_optlong</code>) 10871 were deprecated. 10872 Use their equivalent over <a href="#lua_Integer"><code>lua_Integer</code></a> with a type cast 10873 (or, when possible, use <a href="#lua_Integer"><code>lua_Integer</code></a> in your code). 10874 </li> 10875 10876 </ul> 10877 10878 10879 10880 10881 <h1>9 – <a name="9">The Complete Syntax of Lua</a></h1> 10882 10883 <p> 10884 Here is the complete syntax of Lua in extended BNF. 10885 As usual in extended BNF, 10886 {A} means 0 or more As, 10887 and [A] means an optional A. 10888 (For operator precedences, see <a href="#3.4.8">§3.4.8</a>; 10889 for a description of the terminals 10890 Name, Numeral, 10891 and LiteralString, see <a href="#3.1">§3.1</a>.) 10892 10893 10894 10895 10896 <pre> 10897 10898 chunk ::= block 10899 10900 block ::= {stat} [retstat] 10901 10902 stat ::= ‘<b>;</b>’ | 10903 varlist ‘<b>=</b>’ explist | 10904 functioncall | 10905 label | 10906 <b>break</b> | 10907 <b>goto</b> Name | 10908 <b>do</b> block <b>end</b> | 10909 <b>while</b> exp <b>do</b> block <b>end</b> | 10910 <b>repeat</b> block <b>until</b> exp | 10911 <b>if</b> exp <b>then</b> block {<b>elseif</b> exp <b>then</b> block} [<b>else</b> block] <b>end</b> | 10912 <b>for</b> Name ‘<b>=</b>’ exp ‘<b>,</b>’ exp [‘<b>,</b>’ exp] <b>do</b> block <b>end</b> | 10913 <b>for</b> namelist <b>in</b> explist <b>do</b> block <b>end</b> | 10914 <b>function</b> funcname funcbody | 10915 <b>local</b> <b>function</b> Name funcbody | 10916 <b>local</b> namelist [‘<b>=</b>’ explist] 10917 10918 retstat ::= <b>return</b> [explist] [‘<b>;</b>’] 10919 10920 label ::= ‘<b>::</b>’ Name ‘<b>::</b>’ 10921 10922 funcname ::= Name {‘<b>.</b>’ Name} [‘<b>:</b>’ Name] 10923 10924 varlist ::= var {‘<b>,</b>’ var} 10925 10926 var ::= Name | prefixexp ‘<b>[</b>’ exp ‘<b>]</b>’ | prefixexp ‘<b>.</b>’ Name 10927 10928 namelist ::= Name {‘<b>,</b>’ Name} 10929 10930 explist ::= exp {‘<b>,</b>’ exp} 10931 10932 exp ::= <b>nil</b> | <b>false</b> | <b>true</b> | Numeral | LiteralString | ‘<b>...</b>’ | functiondef | 10933 prefixexp | tableconstructor | exp binop exp | unop exp 10934 10935 prefixexp ::= var | functioncall | ‘<b>(</b>’ exp ‘<b>)</b>’ 10936 10937 functioncall ::= prefixexp args | prefixexp ‘<b>:</b>’ Name args 10938 10939 args ::= ‘<b>(</b>’ [explist] ‘<b>)</b>’ | tableconstructor | LiteralString 10940 10941 functiondef ::= <b>function</b> funcbody 10942 10943 funcbody ::= ‘<b>(</b>’ [parlist] ‘<b>)</b>’ block <b>end</b> 10944 10945 parlist ::= namelist [‘<b>,</b>’ ‘<b>...</b>’] | ‘<b>...</b>’ 10946 10947 tableconstructor ::= ‘<b>{</b>’ [fieldlist] ‘<b>}</b>’ 10948 10949 fieldlist ::= field {fieldsep field} [fieldsep] 10950 10951 field ::= ‘<b>[</b>’ exp ‘<b>]</b>’ ‘<b>=</b>’ exp | Name ‘<b>=</b>’ exp | exp 10952 10953 fieldsep ::= ‘<b>,</b>’ | ‘<b>;</b>’ 10954 10955 binop ::= ‘<b>+</b>’ | ‘<b>-</b>’ | ‘<b>*</b>’ | ‘<b>/</b>’ | ‘<b>//</b>’ | ‘<b>^</b>’ | ‘<b>%</b>’ | 10956 ‘<b>&</b>’ | ‘<b>~</b>’ | ‘<b>|</b>’ | ‘<b>>></b>’ | ‘<b><<</b>’ | ‘<b>..</b>’ | 10957 ‘<b><</b>’ | ‘<b><=</b>’ | ‘<b>></b>’ | ‘<b>>=</b>’ | ‘<b>==</b>’ | ‘<b>~=</b>’ | 10958 <b>and</b> | <b>or</b> 10959 10960 unop ::= ‘<b>-</b>’ | <b>not</b> | ‘<b>#</b>’ | ‘<b>~</b>’ 10961 10962 </pre> 10963 10964 <p> 10965 10966 10967 10968 10969 10970 10971 10972 10973 <P CLASS="footer"> 10974 Last update: 10975 Tue Jun 26 13:16:37 -03 2018 10976 </P> 10977 <!-- 10978 Last change: revised for Lua 5.3.5 10979 --> 10980 10981 </body></html> 10982 10983