1 <html> 2 <head> 3 <title>pcre2limits specification</title> 4 </head> 5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> 6 <h1>pcre2limits man page</h1> 7 <p> 8 Return to the <a href="index.html">PCRE2 index page</a>. 9 </p> 10 <p> 11 This page is part of the PCRE2 HTML documentation. It was generated 12 automatically from the original man page. If there is any nonsense in it, 13 please consult the man page, in case the conversion went wrong. 14 <br> 15 <br><b> 16 SIZE AND OTHER LIMITATIONS 17 </b><br> 18 <P> 19 There are some size limitations in PCRE2 but it is hoped that they will never 20 in practice be relevant. 21 </P> 22 <P> 23 The maximum size of a compiled pattern is approximately 64K code units for the 24 8-bit and 16-bit libraries if PCRE2 is compiled with the default internal 25 linkage size, which is 2 bytes for these libraries. If you want to process 26 regular expressions that are truly enormous, you can compile PCRE2 with an 27 internal linkage size of 3 or 4 (when building the 16-bit library, 3 is rounded 28 up to 4). See the <b>README</b> file in the source distribution and the 29 <a href="pcre2build.html"><b>pcre2build</b></a> 30 documentation for details. In these cases the limit is substantially larger. 31 However, the speed of execution is slower. In the 32-bit library, the internal 32 linkage size is always 4. 33 </P> 34 <P> 35 The maximum length of a source pattern string is essentially unlimited; it is 36 the largest number a PCRE2_SIZE variable can hold. However, the program that 37 calls <b>pcre2_compile()</b> can specify a smaller limit. 38 </P> 39 <P> 40 The maximum length (in code units) of a subject string is one less than the 41 largest number a PCRE2_SIZE variable can hold. PCRE2_SIZE is an unsigned 42 integer type, usually defined as size_t. Its maximum value (that is 43 ~(PCRE2_SIZE)0) is reserved as a special indicator for zero-terminated strings 44 and unset offsets. 45 </P> 46 <P> 47 Note that when using the traditional matching function, PCRE2 uses recursion to 48 handle subpatterns and indefinite repetition. This means that the available 49 stack space may limit the size of a subject string that can be processed by 50 certain patterns. For a discussion of stack issues, see the 51 <a href="pcre2stack.html"><b>pcre2stack</b></a> 52 documentation. 53 </P> 54 <P> 55 All values in repeating quantifiers must be less than 65536. 56 </P> 57 <P> 58 The maximum length of a lookbehind assertion is 65535 characters. 59 </P> 60 <P> 61 There is no limit to the number of parenthesized subpatterns, but there can be 62 no more than 65535 capturing subpatterns. There is, however, a limit to the 63 depth of nesting of parenthesized subpatterns of all kinds. This is imposed in 64 order to limit the amount of system stack used at compile time. The limit can 65 be specified when PCRE2 is built; the default is 250. 66 </P> 67 <P> 68 There is a limit to the number of forward references to subsequent subpatterns 69 of around 200,000. Repeated forward references with fixed upper limits, for 70 example, (?2){0,100} when subpattern number 2 is to the right, are included in 71 the count. There is no limit to the number of backward references. 72 </P> 73 <P> 74 The maximum length of name for a named subpattern is 32 code units, and the 75 maximum number of named subpatterns is 10000. 76 </P> 77 <P> 78 The maximum length of a name in a (*MARK), (*PRUNE), (*SKIP), or (*THEN) verb 79 is 255 for the 8-bit library and 65535 for the 16-bit and 32-bit libraries. 80 </P> 81 <br><b> 82 AUTHOR 83 </b><br> 84 <P> 85 Philip Hazel 86 <br> 87 University Computing Service 88 <br> 89 Cambridge, England. 90 <br> 91 </P> 92 <br><b> 93 REVISION 94 </b><br> 95 <P> 96 Last updated: 05 November 2015 97 <br> 98 Copyright © 1997-2015 University of Cambridge. 99 <br> 100 <p> 101 Return to the <a href="index.html">PCRE2 index page</a>. 102 </p> 103
