pcre *pcre_compile(const char *pattern, int options, " const char **errptr, int *erroffset," " const unsigned char *tableptr);" pcre *pcre_compile2(const char *pattern, int options, " int *errorcodeptr," " const char **errptr, int *erroffset," " const unsigned char *tableptr);" pcre_extra *pcre_study(const pcre *code, int options, " const char **errptr);" void pcre_free_study(pcre_extra *extra); int pcre_exec(const pcre *code, "const pcre_extra *extra," " const char *subject, int length, int startoffset," " int options, int *ovector, int ovecsize);" int pcre_dfa_exec(const pcre *code, "const pcre_extra *extra," " const char *subject, int length, int startoffset," " int options, int *ovector, int ovecsize," " int *workspace, int wscount);". .
int pcre_copy_named_substring(const pcre *code, " const char *subject, int *ovector," " int stringcount, const char *stringname," " char *buffer, int buffersize);" int pcre_copy_substring(const char *subject, int *ovector, " int stringcount, int stringnumber, char *buffer," " int buffersize);" int pcre_get_named_substring(const pcre *code, " const char *subject, int *ovector," " int stringcount, const char *stringname," " const char **stringptr);" int pcre_get_stringnumber(const pcre *code, " const char *name);" int pcre_get_stringtable_entries(const pcre *code, " const char *name, char **first, char **last);" int pcre_get_substring(const char *subject, int *ovector, " int stringcount, int stringnumber," " const char **stringptr);" int pcre_get_substring_list(const char *subject, " int *ovector, int stringcount, const char ***listptr);" void pcre_free_substring(const char *stringptr); void pcre_free_substring_list(const char **stringptr);. .
int pcre_jit_exec(const pcre *code, "const pcre_extra *extra," " const char *subject, int length, int startoffset," " int options, int *ovector, int ovecsize," " pcre_jit_stack *jstack);" pcre_jit_stack *pcre_jit_stack_alloc(int startsize, int maxsize); void pcre_jit_stack_free(pcre_jit_stack *stack); void pcre_assign_jit_stack(pcre_extra *extra, " pcre_jit_callback callback, void *data);" const unsigned char *pcre_maketables(void); int pcre_fullinfo(const pcre *code, "const pcre_extra *extra," " int what, void *where);" int pcre_refcount(pcre *code, int adjust); int pcre_config(int what, void *where); const char *pcre_version(void); int pcre_pattern_to_host_byte_order(pcre *code, " pcre_extra *extra, const unsigned char *tables);". .
void *(*pcre_malloc)(size_t); void (*pcre_free)(void *); void *(*pcre_stack_malloc)(size_t); void (*pcre_stack_free)(void *); int (*pcre_callout)(pcre_callout_block *); int (*pcre_stack_guard)(void);. .
The 16-bit and 32-bit functions operate in the same way as their 8-bit counterparts; they just use different data types for their arguments and results, and their names start with pcre16_ or pcre32_ instead of pcre_. For every option that has UTF8 in its name (for example, PCRE_UTF8), there are corresponding 16-bit and 32-bit names with UTF8 replaced by UTF16 or UTF32, respectively. This facility is in fact just cosmetic; the 16-bit and 32-bit option names define the same bit values.
References to bytes and UTF-8 in this document should be read as references to
16-bit data units and UTF-16 when using the 16-bit library, or 32-bit data
units and UTF-32 when using the 32-bit library, unless specified otherwise.
More details of the specific differences for the 16-bit and 32-bit libraries
are given in the
HREF
pcre16
and
HREF
pcre32
pages.
.
.
pcreposix
documentation. Both of these APIs define a set of C function calls. A C++ wrapper (again for the 8-bit library only) is also distributed with PCRE. It is documented in the HREF
pcrecpp
page.
The native API C function prototypes are defined in the header file pcre.h, and on Unix-like systems the (8-bit) library itself is called libpcre. It can normally be accessed by adding -lpcre to the command for linking an application that uses PCRE. The header file defines the macros PCRE_MAJOR and PCRE_MINOR to contain the major and minor release numbers for the library. Applications can use these to include support for different releases of PCRE.
In a Windows environment, if you want to statically link an application program against a non-dll pcre.a file, you must define PCRE_STATIC before including pcre.h or pcrecpp.h, because otherwise the pcre_malloc() and pcre_free() exported functions will be declared __declspec(dllimport), with unwanted results.
The functions pcre_compile(), pcre_compile2(), pcre_study(),
and pcre_exec() are used for compiling and matching regular expressions
in a Perl-compatible manner. A sample program that demonstrates the simplest
way of using them is provided in the file called pcredemo.c in the PCRE
source distribution. A listing of this program is given in the
HREF
pcredemo
documentation, and the
HREF
pcresample
documentation describes how to compile and run it.
Just-in-time compiler support is an optional feature of PCRE that can be built in appropriate hardware environments. It greatly speeds up the matching performance of many patterns. Simple programs can easily request that it be used if available, by setting an option that is ignored when it is not relevant. More complicated programs might need to make use of the functions pcre_jit_stack_alloc(), pcre_jit_stack_free(), and pcre_assign_jit_stack() in order to control the JIT code's memory usage.
From release 8.32 there is also a direct interface for JIT execution, which
gives improved performance. The JIT-specific functions are discussed in the
HREF
pcrejit
documentation.
A second matching function, pcre_dfa_exec(), which is not
Perl-compatible, is also provided. This uses a different algorithm for the
matching. The alternative algorithm finds all possible matches (at a given
point in the subject), and scans the subject just once (unless there are
lookbehind assertions). However, this algorithm does not return captured
substrings. A description of the two matching algorithms and their advantages
and disadvantages is given in the
HREF
pcrematching
documentation.
In addition to the main compiling and matching functions, there are convenience functions for extracting captured substrings from a subject string that is matched by pcre_exec(). They are: pcre_copy_substring() pcre_copy_named_substring() pcre_get_substring() pcre_get_named_substring() pcre_get_substring_list() pcre_get_stringnumber() pcre_get_stringtable_entries() pcre_free_substring() and pcre_free_substring_list() are also provided, to free the memory used for extracted strings.
The function pcre_maketables() is used to build a set of character tables in the current locale for passing to pcre_compile(), pcre_exec(), or pcre_dfa_exec(). This is an optional facility that is provided for specialist use. Most commonly, no special tables are passed, in which case internal tables that are generated when PCRE is built are used.
The function pcre_fullinfo() is used to find out information about a compiled pattern. The function pcre_version() returns a pointer to a string containing the version of PCRE and its date of release.
The function pcre_refcount() maintains a reference count in a data block containing a compiled pattern. This is provided for the benefit of object-oriented applications.
The global variables pcre_malloc and pcre_free initially contain the entry points of the standard malloc() and free() functions, respectively. PCRE calls the memory management functions via these variables, so a calling program can replace them if it wishes to intercept the calls. This should be done before calling any PCRE functions.
The global variables pcre_stack_malloc and pcre_stack_free are also
indirections to memory management functions. These special functions are used
only when PCRE is compiled to use the heap for remembering data, instead of
recursive function calls, when running the pcre_exec() function. See the
HREF
pcrebuild
documentation for details of how to do this. It is a non-standard way of
building PCRE, for use in environments that have limited stacks. Because of the
greater use of memory management, it runs more slowly. Separate functions are
provided so that special-purpose external code can be used for this case. When
used, these functions are always called in a stack-like manner (last obtained,
first freed), and always for memory blocks of the same size. There is a
discussion about PCRE's stack usage in the
HREF
pcrestack
documentation.
The global variable pcre_callout initially contains NULL. It can be set
by the caller to a "callout" function, which PCRE will then call at specified
points during a matching operation. Details are given in the
HREF
pcrecallout
documentation.
The global variable pcre_stack_guard initially contains NULL. It can be
set by the caller to a function that is called by PCRE whenever it starts
to compile a parenthesized part of a pattern. When parentheses are nested, PCRE
uses recursive function calls, which use up the system stack. This function is
provided so that applications with restricted stacks can force a compilation
error if the stack runs out. The function should return zero if all is well, or
non-zero to force an error.
.
.
HTML <a name="newlines"></a>
Each of the first three conventions is used by at least one operating system as its standard newline sequence. When PCRE is built, a default can be specified. The default default is LF, which is the Unix standard. When PCRE is run, the default can be overridden, either when a pattern is compiled, or when it is matched.
At compile time, the newline convention can be specified by the options
argument of pcre_compile(), or it can be specified by special text at the
start of the pattern itself; this overrides any other settings. See the
HREF
pcrepattern
page for details of the special character sequences.
In the PCRE documentation the word "newline" is used to mean "the character or
pair of characters that indicate a line break". The choice of newline
convention affects the handling of the dot, circumflex, and dollar
metacharacters, the handling of #-comments in /x mode, and, when CRLF is a
recognized line ending sequence, the match position advancement for a
non-anchored pattern. There is more detail about this in the
HTML <a href="#execoptions">
</a>
section on pcre_exec() options
below.
The choice of newline convention does not affect the interpretation of the \en or \er escape sequences, nor does it affect what \eR matches, which is controlled in a similar way, but by separate options. . .
The compiled form of a regular expression is not altered during matching, so the same compiled pattern can safely be used by several threads at once.
If the just-in-time optimization feature is being used, it needs separate
memory stack areas for each thread. See the
HREF
pcrejit
documentation for more details.
.
.
pcreprecompile
documentation, which includes a description of the pcre_pattern_to_host_byte_order() function. However, compiling a regular expression with one version of PCRE for use with a different version is not guaranteed to work and may cause crashes. . .
The function pcre_config() makes it possible for a PCRE client to
discover which optional features have been compiled into the PCRE library. The
HREF
pcrebuild
documentation has more details about these optional features.
The first argument for pcre_config() is an integer, specifying which
information is required; the second argument is a pointer to a variable into
which the information is placed. The returned value is zero on success, or the
negative error code PCRE_ERROR_BADOPTION if the value in the first argument is
not recognized. The following information is available:
PCRE_CONFIG_UTF8
The output is an integer that is set to one if UTF-8 support is available;
otherwise it is set to zero. This value should normally be given to the 8-bit
version of this function, pcre_config(). If it is given to the 16-bit
or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION.
PCRE_CONFIG_UTF16
The output is an integer that is set to one if UTF-16 support is available;
otherwise it is set to zero. This value should normally be given to the 16-bit
version of this function, pcre16_config(). If it is given to the 8-bit
or 32-bit version of this function, the result is PCRE_ERROR_BADOPTION.
PCRE_CONFIG_UTF32
The output is an integer that is set to one if UTF-32 support is available;
otherwise it is set to zero. This value should normally be given to the 32-bit
version of this function, pcre32_config(). If it is given to the 8-bit
or 16-bit version of this function, the result is PCRE_ERROR_BADOPTION.
PCRE_CONFIG_UNICODE_PROPERTIES
The output is an integer that is set to one if support for Unicode character
properties is available; otherwise it is set to zero.
PCRE_CONFIG_JIT
The output is an integer that is set to one if support for just-in-time
compiling is available; otherwise it is set to zero.
PCRE_CONFIG_JITTARGET
The output is a pointer to a zero-terminated "const char *" string. If JIT
support is available, the string contains the name of the architecture for
which the JIT compiler is configured, for example "x86 32bit (little endian +
unaligned)". If JIT support is not available, the result is NULL.
PCRE_CONFIG_NEWLINE
The output is an integer whose value specifies the default character sequence
that is recognized as meaning "newline". The values that are supported in
ASCII/Unicode environments are: 10 for LF, 13 for CR, 3338 for CRLF, -2 for
ANYCRLF, and -1 for ANY. In EBCDIC environments, CR, ANYCRLF, and ANY yield the
same values. However, the value for LF is normally 21, though some EBCDIC
environments use 37. The corresponding values for CRLF are 3349 and 3365. The
default should normally correspond to the standard sequence for your operating
system.
PCRE_CONFIG_BSR
The output is an integer whose value indicates what character sequences the \eR
escape sequence matches by default. A value of 0 means that \eR matches any
Unicode line ending sequence; a value of 1 means that \eR matches only CR, LF,
or CRLF. The default can be overridden when a pattern is compiled or matched.
PCRE_CONFIG_LINK_SIZE
The output is an integer that contains the number of bytes used for internal
linkage in compiled regular expressions. For the 8-bit library, the value can
be 2, 3, or 4. For the 16-bit library, the value is either 2 or 4 and is still
a number of bytes. For the 32-bit library, the value is either 2 or 4 and is
still a number of bytes. The default value of 2 is sufficient for all but the
most massive patterns, since it allows the compiled pattern to be up to 64K in
size. Larger values allow larger regular expressions to be compiled, at the
expense of slower matching.
PCRE_CONFIG_POSIX_MALLOC_THRESHOLD
The output is an integer that contains the threshold above which the POSIX
interface uses malloc() for output vectors. Further details are given in
the
HREF
pcreposix
documentation.
PCRE_CONFIG_PARENS_LIMIT
The output is a long integer that gives the maximum depth of nesting of
parentheses (of any kind) in a pattern. This limit is imposed to cap the amount
of system stack used when a pattern is compiled. It is specified when PCRE is
built; the default is 250. This limit does not take into account the stack that
may already be used by the calling application. For finer control over
compilation stack usage, you can set a pointer to an external checking function
in pcre_stack_guard.
PCRE_CONFIG_MATCH_LIMIT
The output is a long integer that gives the default limit for the number of
internal matching function calls in a pcre_exec() execution. Further
details are given with pcre_exec() below.
PCRE_CONFIG_MATCH_LIMIT_RECURSION
The output is a long integer that gives the default limit for the depth of
recursion when calling the internal matching function in a pcre_exec()
execution. Further details are given with pcre_exec() below.
PCRE_CONFIG_STACKRECURSE
The output is an integer that is set to one if internal recursion when running
pcre_exec() is implemented by recursive function calls that use the stack
to remember their state. This is the usual way that PCRE is compiled. The
output is zero if PCRE was compiled to use blocks of data on the heap instead
of recursive function calls. In this case, pcre_stack_malloc and
pcre_stack_free are called to manage memory blocks on the heap, thus
avoiding the use of the stack.
.
.
pcre *pcre_compile(const char *pattern, int options, " const char **errptr, int *erroffset," " const unsigned char *tableptr);" pcre *pcre_compile2(const char *pattern, int options, " int *errorcodeptr," " const char **errptr, int *erroffset," " const unsigned char *tableptr);"
Either of the functions pcre_compile() or pcre_compile2() can be called to compile a pattern into an internal form. The only difference between the two interfaces is that pcre_compile2() has an additional argument, errorcodeptr, via which a numerical error code can be returned. To avoid too much repetition, we refer just to pcre_compile() below, but the information applies equally to pcre_compile2().
The pattern is a C string terminated by a binary zero, and is passed in the pattern argument. A pointer to a single block of memory that is obtained via pcre_malloc is returned. This contains the compiled code and related data. The pcre type is defined for the returned block; this is a typedef for a structure whose contents are not externally defined. It is up to the caller to free the memory (via pcre_free) when it is no longer required.
Although the compiled code of a PCRE regex is relocatable, that is, it does not depend on memory location, the complete pcre data block is not fully relocatable, because it may contain a copy of the tableptr argument, which is an address (see below).
The options argument contains various bit settings that affect the
compilation. It should be zero if no options are required. The available
options are described below. Some of them (in particular, those that are
compatible with Perl, but some others as well) can also be set and unset from
within the pattern (see the detailed description in the
HREF
pcrepattern
documentation). For those options that can be different in different parts of
the pattern, the contents of the options argument specifies their
settings at the start of compilation and execution. The PCRE_ANCHORED,
PCRE_BSR_xxx, PCRE_NEWLINE_xxx, PCRE_NO_UTF8_CHECK, and
PCRE_NO_START_OPTIMIZE options can be set at the time of matching as well as at
compile time.
If errptr is NULL, pcre_compile() returns NULL immediately. Otherwise, if compilation of a pattern fails, pcre_compile() returns NULL, and sets the variable pointed to by errptr to point to a textual error message. This is a static string that is part of the library. You must not try to free it. Normally, the offset from the start of the pattern to the data unit that was being processed when the error was discovered is placed in the variable pointed to by erroffset, which must not be NULL (if it is, an immediate error is given). However, for an invalid UTF-8 or UTF-16 string, the offset is that of the first data unit of the failing character.
Some errors are not detected until the whole pattern has been scanned; in these cases, the offset passed back is the length of the pattern. Note that the offset is in data units, not characters, even in a UTF mode. It may sometimes point into the middle of a UTF-8 or UTF-16 character.
If pcre_compile2() is used instead of pcre_compile(), and the errorcodeptr argument is not NULL, a non-zero error code number is returned via this argument in the event of an error. This is in addition to the textual error message. Error codes and messages are listed below.
If the final argument, tableptr, is NULL, PCRE uses a default set of character tables that are built when PCRE is compiled, using the default C locale. Otherwise, tableptr must be an address that is the result of a call to pcre_maketables(). This value is stored with the compiled pattern, and used again by pcre_exec() and pcre_dfa_exec() when the pattern is matched. For more discussion, see the section on locale support below.
This code fragment shows a typical straightforward call to pcre_compile():
pcre *re;
const char *error;
int erroffset;
re = pcre_compile(
"^A.*Z", /* the pattern */
0, /* default options */
&error, /* for error message */
&erroffset, /* for error offset */
NULL); /* use default character tables */
The following names for option bits are defined in the pcre.h header
file:
PCRE_ANCHORED
If this bit is set, the pattern is forced to be "anchored", that is, it is
constrained to match only at the first matching point in the string that is
being searched (the "subject string"). This effect can also be achieved by
appropriate constructs in the pattern itself, which is the only way to do it in
Perl.
PCRE_AUTO_CALLOUT
If this bit is set, pcre_compile() automatically inserts callout items,
all with number 255, before each pattern item. For discussion of the callout
facility, see the
HREF
pcrecallout
documentation.
PCRE_BSR_ANYCRLF
PCRE_BSR_UNICODE
These options (which are mutually exclusive) control what the \eR escape
sequence matches. The choice is either to match only CR, LF, or CRLF, or to
match any Unicode newline sequence. The default is specified when PCRE is
built. It can be overridden from within the pattern, or by setting an option
when a compiled pattern is matched.
PCRE_CASELESS
If this bit is set, letters in the pattern match both upper and lower case
letters. It is equivalent to Perl's /i option, and it can be changed within a
pattern by a (?i) option setting. In UTF-8 mode, PCRE always understands the
concept of case for characters whose values are less than 128, so caseless
matching is always possible. For characters with higher values, the concept of
case is supported if PCRE is compiled with Unicode property support, but not
otherwise. If you want to use caseless matching for characters 128 and above,
you must ensure that PCRE is compiled with Unicode property support as well as
with UTF-8 support.
PCRE_DOLLAR_ENDONLY
If this bit is set, a dollar metacharacter in the pattern matches only at the
end of the subject string. Without this option, a dollar also matches
immediately before a newline at the end of the string (but not before any other
newlines). The PCRE_DOLLAR_ENDONLY option is ignored if PCRE_MULTILINE is set.
There is no equivalent to this option in Perl, and no way to set it within a
pattern.
PCRE_DOTALL
If this bit is set, a dot metacharacter in the pattern matches a character of
any value, including one that indicates a newline. However, it only ever
matches one character, even if newlines are coded as CRLF. Without this option,
a dot does not match when the current position is at a newline. This option is
equivalent to Perl's /s option, and it can be changed within a pattern by a
(?s) option setting. A negative class such as [^a] always matches newline
characters, independent of the setting of this option.
PCRE_DUPNAMES
If this bit is set, names used to identify capturing subpatterns need not be
unique. This can be helpful for certain types of pattern when it is known that
only one instance of the named subpattern can ever be matched. There are more
details of named subpatterns below; see also the
HREF
pcrepattern
documentation.
PCRE_EXTENDED
If this bit is set, most white space characters in the pattern are totally
ignored except when escaped or inside a character class. However, white space
is not allowed within sequences such as (?> that introduce various
parenthesized subpatterns, nor within a numerical quantifier such as {1,3}.
However, ignorable white space is permitted between an item and a following
quantifier and between a quantifier and a following + that indicates
possessiveness.
White space did not used to include the VT character (code 11), because Perl did not treat this character as white space. However, Perl changed at release 5.18, so PCRE followed at release 8.34, and VT is now treated as white space.
PCRE_EXTENDED also causes characters between an unescaped # outside a character class and the next newline, inclusive, to be ignored. PCRE_EXTENDED is equivalent to Perl's /x option, and it can be changed within a pattern by a (?x) option setting.
Which characters are interpreted as newlines is controlled by the options
passed to pcre_compile() or by a special sequence at the start of the
pattern, as described in the section entitled
HTML <a href="pcrepattern.html#newlines">
</a>
"Newline conventions"
in the pcrepattern documentation. Note that the end of this type of
comment is a literal newline sequence in the pattern; escape sequences that
happen to represent a newline do not count.
This option makes it possible to include comments inside complicated patterns. Note, however, that this applies only to data characters. White space characters may never appear within special character sequences in a pattern, for example within the sequence (?( that introduces a conditional subpattern. PCRE_EXTRA This option was invented in order to turn on additional functionality of PCRE that is incompatible with Perl, but it is currently of very little use. When set, any backslash in a pattern that is followed by a letter that has no special meaning causes an error, thus reserving these combinations for future expansion. By default, as in Perl, a backslash followed by a letter with no special meaning is treated as a literal. (Perl can, however, be persuaded to give an error for this, by running it with the -w option.) There are at present no other features controlled by this option. It can also be set by a (?X) option setting within a pattern. PCRE_FIRSTLINE If this option is set, an unanchored pattern is required to match before or at the first newline in the subject string, though the matched text may continue over the newline. PCRE_JAVASCRIPT_COMPAT If this option is set, PCRE's behaviour is changed in some ways so that it is compatible with JavaScript rather than Perl. The changes are as follows:
(1) A lone closing square bracket in a pattern causes a compile-time error, because this is illegal in JavaScript (by default it is treated as a data character). Thus, the pattern AB]CD becomes illegal when this option is set.
(2) At run time, a back reference to an unset subpattern group matches an empty string (by default this causes the current matching alternative to fail). A pattern such as (\e1)(a) succeeds when this option is set (assuming it can find an "a" in the subject), whereas it fails by default, for Perl compatibility.
(3) \eU matches an upper case "U" character; by default \eU causes a compile time error (Perl uses \eU to upper case subsequent characters).
(4) \eu matches a lower case "u" character unless it is followed by four hexadecimal digits, in which case the hexadecimal number defines the code point to match. By default, \eu causes a compile time error (Perl uses it to upper case the following character).
(5) \ex matches a lower case "x" character unless it is followed by two hexadecimal digits, in which case the hexadecimal number defines the code point to match. By default, as in Perl, a hexadecimal number is always expected after \ex, but it may have zero, one, or two digits (so, for example, \exz matches a binary zero character followed by z). PCRE_MULTILINE By default, for the purposes of matching "start of line" and "end of line", PCRE treats the subject string as consisting of a single line of characters, even if it actually contains newlines. The "start of line" metacharacter (^) matches only at the start of the string, and the "end of line" metacharacter ($) matches only at the end of the string, or before a terminating newline (except when PCRE_DOLLAR_ENDONLY is set). Note, however, that unless PCRE_DOTALL is set, the "any character" metacharacter (.) does not match at a newline. This behaviour (for ^, $, and dot) is the same as Perl.
When PCRE_MULTILINE it is set, the "start of line" and "end of line" constructs match immediately following or immediately before internal newlines in the subject string, respectively, as well as at the very start and end. This is equivalent to Perl's /m option, and it can be changed within a pattern by a (?m) option setting. If there are no newlines in a subject string, or no occurrences of ^ or $ in a pattern, setting PCRE_MULTILINE has no effect. PCRE_NEVER_UTF This option locks out interpretation of the pattern as UTF-8 (or UTF-16 or UTF-32 in the 16-bit and 32-bit libraries). In particular, it prevents the creator of the pattern from switching to UTF interpretation by starting the pattern with (*UTF). This may be useful in applications that process patterns from external sources. The combination of PCRE_UTF8 and PCRE_NEVER_UTF also causes an error. PCRE_NEWLINE_CR PCRE_NEWLINE_LF PCRE_NEWLINE_CRLF PCRE_NEWLINE_ANYCRLF PCRE_NEWLINE_ANY These options override the default newline definition that was chosen when PCRE was built. Setting the first or the second specifies that a newline is indicated by a single character (CR or LF, respectively). Setting PCRE_NEWLINE_CRLF specifies that a newline is indicated by the two-character CRLF sequence. Setting PCRE_NEWLINE_ANYCRLF specifies that any of the three preceding sequences should be recognized. Setting PCRE_NEWLINE_ANY specifies that any Unicode newline sequence should be recognized.
In an ASCII/Unicode environment, the Unicode newline sequences are the three just mentioned, plus the single characters VT (vertical tab, U+000B), FF (form feed, U+000C), NEL (next line, U+0085), LS (line separator, U+2028), and PS (paragraph separator, U+2029). For the 8-bit library, the last two are recognized only in UTF-8 mode.
When PCRE is compiled to run in an EBCDIC (mainframe) environment, the code for
CR is 0x0d, the same as ASCII. However, the character code for LF is normally
0x15, though in some EBCDIC environments 0x25 is used. Whichever of these is
not LF is made to correspond to Unicode's NEL character. EBCDIC codes are all
less than 256. For more details, see the
HREF
pcrebuild
documentation.
The newline setting in the options word uses three bits that are treated as a number, giving eight possibilities. Currently only six are used (default plus the five values above). This means that if you set more than one newline option, the combination may or may not be sensible. For example, PCRE_NEWLINE_CR with PCRE_NEWLINE_LF is equivalent to PCRE_NEWLINE_CRLF, but other combinations may yield unused numbers and cause an error.
The only time that a line break in a pattern is specially recognized when compiling is when PCRE_EXTENDED is set. CR and LF are white space characters, and so are ignored in this mode. Also, an unescaped # outside a character class indicates a comment that lasts until after the next line break sequence. In other circumstances, line break sequences in patterns are treated as literal data.
The newline option that is set at compile time becomes the default that is used
for pcre_exec() and pcre_dfa_exec(), but it can be overridden.
PCRE_NO_AUTO_CAPTURE
If this option is set, it disables the use of numbered capturing parentheses in
the pattern. Any opening parenthesis that is not followed by ? behaves as if it
were followed by ?: but named parentheses can still be used for capturing (and
they acquire numbers in the usual way). There is no equivalent of this option
in Perl.
PCRE_NO_AUTO_POSSESS
If this option is set, it disables "auto-possessification". This is an
optimization that, for example, turns a+b into a++b in order to avoid
backtracks into a+ that can never be successful. However, if callouts are in
use, auto-possessification means that some of them are never taken. You can set
this option if you want the matching functions to do a full unoptimized search
and run all the callouts, but it is mainly provided for testing purposes.
PCRE_NO_START_OPTIMIZE
This is an option that acts at matching time; that is, it is really an option
for pcre_exec() or pcre_dfa_exec(). If it is set at compile time,
it is remembered with the compiled pattern and assumed at matching time. This
is necessary if you want to use JIT execution, because the JIT compiler needs
to know whether or not this option is set. For details see the discussion of
PCRE_NO_START_OPTIMIZE
HTML <a href="#execoptions">
</a>
below.
PCRE_UCP
This option changes the way PCRE processes \eB, \eb, \eD, \ed, \eS, \es, \eW,
\ew, and some of the POSIX character classes. By default, only ASCII characters
are recognized, but if PCRE_UCP is set, Unicode properties are used instead to
classify characters. More details are given in the section on
HTML <a href="pcre.html#genericchartypes">
</a>
generic character types
in the
HREF
pcrepattern
page. If you set PCRE_UCP, matching one of the items it affects takes much
longer. The option is available only if PCRE has been compiled with Unicode
property support.
PCRE_UNGREEDY
This option inverts the "greediness" of the quantifiers so that they are not
greedy by default, but become greedy if followed by "?". It is not compatible
with Perl. It can also be set by a (?U) option setting within the pattern.
PCRE_UTF8
This option causes PCRE to regard both the pattern and the subject as strings
of UTF-8 characters instead of single-byte strings. However, it is available
only when PCRE is built to include UTF support. If not, the use of this option
provokes an error. Details of how this option changes the behaviour of PCRE are
given in the
HREF
pcreunicode
page.
PCRE_NO_UTF8_CHECK
When PCRE_UTF8 is set, the validity of the pattern as a UTF-8 string is
automatically checked. There is a discussion about the
HTML <a href="pcreunicode.html#utf8strings">
</a>
validity of UTF-8 strings
in the
HREF
pcreunicode
page. If an invalid UTF-8 sequence is found, pcre_compile() returns an
error. If you already know that your pattern is valid, and you want to skip
this check for performance reasons, you can set the PCRE_NO_UTF8_CHECK option.
When it is set, the effect of passing an invalid UTF-8 string as a pattern is
undefined. It may cause your program to crash or loop. Note that this option
can also be passed to pcre_exec() and pcre_dfa_exec(), to suppress
the validity checking of subject strings only. If the same string is being
matched many times, the option can be safely set for the second and subsequent
matchings to improve performance.
.
.
pcre_extra *pcre_study(const pcre *code, int options, " const char **errptr);"
If a compiled pattern is going to be used several times, it is worth spending more time analyzing it in order to speed up the time taken for matching. The function pcre_study() takes a pointer to a compiled pattern as its first argument. If studying the pattern produces additional information that will help speed up matching, pcre_study() returns a pointer to a pcre_extra block, in which the study_data field points to the results of the study.
The returned value from pcre_study() can be passed directly to
pcre_exec() or pcre_dfa_exec(). However, a pcre_extra block
also contains other fields that can be set by the caller before the block is
passed; these are described
HTML <a href="#extradata">
</a>
below
in the section on matching a pattern.
If studying the pattern does not produce any useful information, pcre_study() returns NULL by default. In that circumstance, if the calling program wants to pass any of the other fields to pcre_exec() or pcre_dfa_exec(), it must set up its own pcre_extra block. However, if pcre_study() is called with the PCRE_STUDY_EXTRA_NEEDED option, it returns a pcre_extra block even if studying did not find any additional information. It may still return NULL, however, if an error occurs in pcre_study().
The second argument of pcre_study() contains option bits. There are three further options in addition to PCRE_STUDY_EXTRA_NEEDED: PCRE_STUDY_JIT_COMPILE PCRE_STUDY_JIT_PARTIAL_HARD_COMPILE PCRE_STUDY_JIT_PARTIAL_SOFT_COMPILE If any of these are set, and the just-in-time compiler is available, the pattern is further compiled into machine code that executes much faster than the pcre_exec() interpretive matching function. If the just-in-time compiler is not available, these options are ignored. All undefined bits in the options argument must be zero.
JIT compilation is a heavyweight optimization. It can take some time for
patterns to be analyzed, and for one-off matches and simple patterns the
benefit of faster execution might be offset by a much slower study time.
Not all patterns can be optimized by the JIT compiler. For those that cannot be
handled, matching automatically falls back to the pcre_exec()
interpreter. For more details, see the
HREF
pcrejit
documentation.
The third argument for pcre_study() is a pointer for an error message. If studying succeeds (even if no data is returned), the variable it points to is set to NULL. Otherwise it is set to point to a textual error message. This is a static string that is part of the library. You must not try to free it. You should test the error pointer for NULL after calling pcre_study(), to be sure that it has run successfully.
When you are finished with a pattern, you can free the memory used for the study data by calling pcre_free_study(). This function was added to the API for release 8.20. For earlier versions, the memory could be freed with pcre_free(), just like the pattern itself. This will still work in cases where JIT optimization is not used, but it is advisable to change to the new function when convenient.
This is a typical way in which pcre_study() is used (except that in a real application there should be tests for errors): int rc; pcre *re; pcre_extra *sd; re = pcre_compile("pattern", 0, &error, &erroroffset, NULL); sd = pcre_study( re, /* result of pcre_compile() */ 0, /* no options */ &error); /* set to NULL or points to a message */ rc = pcre_exec( /* see below for details of pcre_exec() options */ re, sd, "subject", 7, 0, 0, ovector, 30); ... pcre_free_study(sd); pcre_free(re); Studying a pattern does two things: first, a lower bound for the length of subject string that is needed to match the pattern is computed. This does not mean that there are any strings of that length that match, but it does guarantee that no shorter strings match. The value is used to avoid wasting time by trying to match strings that are shorter than the lower bound. You can find out the value in a calling program via the pcre_fullinfo() function.
Studying a pattern is also useful for non-anchored patterns that do not have a single fixed starting character. A bitmap of possible starting bytes is created. This speeds up finding a position in the subject at which to start matching. (In 16-bit mode, the bitmap is used for 16-bit values less than 256. In 32-bit mode, the bitmap is used for 32-bit values less than 256.)
These two optimizations apply to both pcre_exec() and pcre_dfa_exec(), and the information is also used by the JIT compiler. The optimizations can be disabled by setting the PCRE_NO_START_OPTIMIZE option. You might want to do this if your pattern contains callouts or (*MARK) and you want to make use of these facilities in cases where matching fails.
PCRE_NO_START_OPTIMIZE can be specified at either compile time or execution time. However, if PCRE_NO_START_OPTIMIZE is passed to pcre_exec(), (that is, after any JIT compilation has happened) JIT execution is disabled. For JIT execution to work with PCRE_NO_START_OPTIMIZE, the option must be set at compile time.
There is a longer discussion of PCRE_NO_START_OPTIMIZE
HTML <a href="#execoptions">
</a>
below.
.
.
HTML <a name="localesupport"></a>
The use of locales with Unicode is discouraged. If you are handling characters with code points greater than 128, you should either use Unicode support, or use locales, but not try to mix the two.
PCRE contains an internal set of tables that are used when the final argument of pcre_compile() is NULL. These are sufficient for many applications. Normally, the internal tables recognize only ASCII characters. However, when PCRE is built, it is possible to cause the internal tables to be rebuilt in the default "C" locale of the local system, which may cause them to be different.
The internal tables can always be overridden by tables supplied by the application that calls PCRE. These may be created in a different locale from the default. As more and more applications change to using Unicode, the need for this locale support is expected to die away.
External tables are built by calling the pcre_maketables() function, which has no arguments, in the relevant locale. The result can then be passed to pcre_compile() as often as necessary. For example, to build and use tables that are appropriate for the French locale (where accented characters with values greater than 128 are treated as letters), the following code could be used: setlocale(LC_CTYPE, "fr_FR"); tables = pcre_maketables(); re = pcre_compile(..., tables); The locale name "fr_FR" is used on Linux and other Unix-like systems; if you are using Windows, the name for the French locale is "french".
When pcre_maketables() runs, the tables are built in memory that is obtained via pcre_malloc. It is the caller's responsibility to ensure that the memory containing the tables remains available for as long as it is needed.
The pointer that is passed to pcre_compile() is saved with the compiled pattern, and the same tables are used via this pointer by pcre_study() and also by pcre_exec() and pcre_dfa_exec(). Thus, for any single pattern, compilation, studying and matching all happen in the same locale, but different patterns can be processed in different locales.
It is possible to pass a table pointer or NULL (indicating the use of the
internal tables) to pcre_exec() or pcre_dfa_exec() (see the
discussion below in the section on matching a pattern). This facility is
provided for use with pre-compiled patterns that have been saved and reloaded.
Character tables are not saved with patterns, so if a non-standard table was
used at compile time, it must be provided again when the reloaded pattern is
matched. Attempting to use this facility to match a pattern in a different
locale from the one in which it was compiled is likely to lead to anomalous
(usually incorrect) results.
.
.
HTML <a name="infoaboutpattern"></a>
int pcre_fullinfo(const pcre *code, "const pcre_extra *extra," " int what, void *where);"
The pcre_fullinfo() function returns information about a compiled pattern. It replaces the pcre_info() function, which was removed from the library at version 8.30, after more than 10 years of obsolescence.
The first argument for pcre_fullinfo() is a pointer to the compiled pattern. The second argument is the result of pcre_study(), or NULL if the pattern was not studied. The third argument specifies which piece of information is required, and the fourth argument is a pointer to a variable to receive the data. The yield of the function is zero for success, or one of the following negative numbers: PCRE_ERROR_NULL the argument code was NULL the argument where was NULL PCRE_ERROR_BADMAGIC the "magic number" was not found PCRE_ERROR_BADENDIANNESS the pattern was compiled with different endianness PCRE_ERROR_BADOPTION the value of what was invalid PCRE_ERROR_UNSET the requested field is not set The "magic number" is placed at the start of each compiled pattern as an simple check against passing an arbitrary memory pointer. The endianness error can occur if a compiled pattern is saved and reloaded on a different host. Here is a typical call of pcre_fullinfo(), to obtain the length of the compiled pattern: int rc; size_t length; rc = pcre_fullinfo( re, /* result of pcre_compile() */ sd, /* result of pcre_study(), or NULL */ PCRE_INFO_SIZE, /* what is required */ &length); /* where to put the data */ The possible values for the third argument are defined in pcre.h, and are as follows: PCRE_INFO_BACKREFMAX Return the number of the highest back reference in the pattern. The fourth argument should point to an int variable. Zero is returned if there are no back references. PCRE_INFO_CAPTURECOUNT Return the number of capturing subpatterns in the pattern. The fourth argument should point to an int variable. PCRE_INFO_DEFAULT_TABLES Return a pointer to the internal default character tables within PCRE. The fourth argument should point to an unsigned char * variable. This information call is provided for internal use by the pcre_study() function. External callers can cause PCRE to use its internal tables by passing a NULL table pointer. PCRE_INFO_FIRSTBYTE (deprecated) Return information about the first data unit of any matched string, for a non-anchored pattern. The name of this option refers to the 8-bit library, where data units are bytes. The fourth argument should point to an int variable. Negative values are used for special cases. However, this means that when the 32-bit library is in non-UTF-32 mode, the full 32-bit range of characters cannot be returned. For this reason, this value is deprecated; use PCRE_INFO_FIRSTCHARACTERFLAGS and PCRE_INFO_FIRSTCHARACTER instead.
If there is a fixed first value, for example, the letter "c" from a pattern such as (cat|cow|coyote), its value is returned. In the 8-bit library, the value is always less than 256. In the 16-bit library the value can be up to 0xffff. In the 32-bit library the value can be up to 0x10ffff.
If there is no fixed first value, and if either (a) the pattern was compiled with the PCRE_MULTILINE option, and every branch starts with "^", or (b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set (if it were set, the pattern would be anchored), -1 is returned, indicating that the pattern matches only at the start of a subject string or after any newline within the string. Otherwise -2 is returned. For anchored patterns, -2 is returned. PCRE_INFO_FIRSTCHARACTER Return the value of the first data unit (non-UTF character) of any matched string in the situation where PCRE_INFO_FIRSTCHARACTERFLAGS returns 1; otherwise return 0. The fourth argument should point to an uint_t variable.
In the 8-bit library, the value is always less than 256. In the 16-bit library the value can be up to 0xffff. In the 32-bit library in UTF-32 mode the value can be up to 0x10ffff, and up to 0xffffffff when not using UTF-32 mode. PCRE_INFO_FIRSTCHARACTERFLAGS Return information about the first data unit of any matched string, for a non-anchored pattern. The fourth argument should point to an int variable.
If there is a fixed first value, for example, the letter "c" from a pattern
such as (cat|cow|coyote), 1 is returned, and the character value can be
retrieved using PCRE_INFO_FIRSTCHARACTER. If there is no fixed first value, and
if either
(a) the pattern was compiled with the PCRE_MULTILINE option, and every branch
starts with "^", or
(b) every branch of the pattern starts with ".*" and PCRE_DOTALL is not set
(if it were set, the pattern would be anchored),
2 is returned, indicating that the pattern matches only at the start of a
subject string or after any newline within the string. Otherwise 0 is
returned. For anchored patterns, 0 is returned.
PCRE_INFO_FIRSTTABLE
If the pattern was studied, and this resulted in the construction of a 256-bit
table indicating a fixed set of values for the first data unit in any matching
string, a pointer to the table is returned. Otherwise NULL is returned. The
fourth argument should point to an unsigned char * variable.
PCRE_INFO_HASCRORLF
Return 1 if the pattern contains any explicit matches for CR or LF characters,
otherwise 0. The fourth argument should point to an int variable. An
explicit match is either a literal CR or LF character, or \er or \en.
PCRE_INFO_JCHANGED
Return 1 if the (?J) or (?-J) option setting is used in the pattern, otherwise
0. The fourth argument should point to an int variable. (?J) and
(?-J) set and unset the local PCRE_DUPNAMES option, respectively.
PCRE_INFO_JIT
Return 1 if the pattern was studied with one of the JIT options, and
just-in-time compiling was successful. The fourth argument should point to an
int variable. A return value of 0 means that JIT support is not available
in this version of PCRE, or that the pattern was not studied with a JIT option,
or that the JIT compiler could not handle this particular pattern. See the
HREF
pcrejit
documentation for details of what can and cannot be handled.
PCRE_INFO_JITSIZE
If the pattern was successfully studied with a JIT option, return the size of
the JIT compiled code, otherwise return zero. The fourth argument should point
to a size_t variable.
PCRE_INFO_LASTLITERAL
Return the value of the rightmost literal data unit that must exist in any
matched string, other than at its start, if such a value has been recorded. The
fourth argument should point to an int variable. If there is no such
value, -1 is returned. For anchored patterns, a last literal value is recorded
only if it follows something of variable length. For example, for the pattern
/^a\ed+z\ed+/ the returned value is "z", but for /^a\edz\ed/ the returned value
is -1.
Since for the 32-bit library using the non-UTF-32 mode, this function is unable to return the full 32-bit range of characters, this value is deprecated; instead the PCRE_INFO_REQUIREDCHARFLAGS and PCRE_INFO_REQUIREDCHAR values should be used. PCRE_INFO_MATCH_EMPTY Return 1 if the pattern can match an empty string, otherwise 0. The fourth argument should point to an int variable. PCRE_INFO_MATCHLIMIT If the pattern set a match limit by including an item of the form (*LIMIT_MATCH=nnnn) at the start, the value is returned. The fourth argument should point to an unsigned 32-bit integer. If no such value has been set, the call to pcre_fullinfo() returns the error PCRE_ERROR_UNSET. PCRE_INFO_MAXLOOKBEHIND Return the number of characters (NB not data units) in the longest lookbehind assertion in the pattern. This information is useful when doing multi-segment matching using the partial matching facilities. Note that the simple assertions \eb and \eB require a one-character lookbehind. \eA also registers a one-character lookbehind, though it does not actually inspect the previous character. This is to ensure that at least one character from the old segment is retained when a new segment is processed. Otherwise, if there are no lookbehinds in the pattern, \eA might match incorrectly at the start of a new segment. PCRE_INFO_MINLENGTH If the pattern was studied and a minimum length for matching subject strings was computed, its value is returned. Otherwise the returned value is -1. The value is a number of characters, which in UTF mode may be different from the number of data units. The fourth argument should point to an int variable. A non-negative value is a lower bound to the length of any matching string. There may not be any strings of that length that do actually match, but every string that does match is at least that long. PCRE_INFO_NAMECOUNT PCRE_INFO_NAMEENTRYSIZE PCRE_INFO_NAMETABLE PCRE supports the use of named as well as numbered capturing parentheses. The names are just an additional way of identifying the parentheses, which still acquire numbers. Several convenience functions such as pcre_get_named_substring() are provided for extracting captured substrings by name. It is also possible to extract the data directly, by first converting the name to a number in order to access the correct pointers in the output vector (described with pcre_exec() below). To do the conversion, you need to use the name-to-number map, which is described by these three values.
The map consists of a number of fixed-size entries. PCRE_INFO_NAMECOUNT gives the number of entries, and PCRE_INFO_NAMEENTRYSIZE gives the size of each entry; both of these return an int value. The entry size depends on the length of the longest name. PCRE_INFO_NAMETABLE returns a pointer to the first entry of the table. This is a pointer to char in the 8-bit library, where the first two bytes of each entry are the number of the capturing parenthesis, most significant byte first. In the 16-bit library, the pointer points to 16-bit data units, the first of which contains the parenthesis number. In the 32-bit library, the pointer points to 32-bit data units, the first of which contains the parenthesis number. The rest of the entry is the corresponding name, zero terminated.
The names are in alphabetical order. If (?| is used to create multiple groups
with the same number, as described in the
HTML <a href="pcrepattern.html#dupsubpatternnumber">
</a>
section on duplicate subpattern numbers
in the
HREF
pcrepattern
page, the groups may be given the same name, but there is only one entry in the
table. Different names for groups of the same number are not permitted.
Duplicate names for subpatterns with different numbers are permitted,
but only if PCRE_DUPNAMES is set. They appear in the table in the order in
which they were found in the pattern. In the absence of (?| this is the order
of increasing number; when (?| is used this is not necessarily the case because
later subpatterns may have lower numbers.
As a simple example of the name/number table, consider the following pattern
after compilation by the 8-bit library (assume PCRE_EXTENDED is set, so white
space - including newlines - is ignored):
JOIN
(?<date> (?<year>(\ed\ed)?\ed\ed) -
(?<month>\ed\ed) - (?<day>\ed\ed) )
There are four named subpatterns, so the table has four entries, and each entry
in the table is eight bytes long. The table is as follows, with non-printing
bytes shows in hexadecimal, and undefined bytes shown as ??:
00 01 d a t e 00 ??
00 05 d a y 00 ?? ??
00 04 m o n t h 00
00 02 y e a r 00 ??
When writing code to extract data from named subpatterns using the
name-to-number map, remember that the length of the entries is likely to be
different for each compiled pattern.
PCRE_INFO_OKPARTIAL
Return 1 if the pattern can be used for partial matching with
pcre_exec(), otherwise 0. The fourth argument should point to an
int variable. From release 8.00, this always returns 1, because the
restrictions that previously applied to partial matching have been lifted. The
HREF
pcrepartial
documentation gives details of partial matching.
PCRE_INFO_OPTIONS
Return a copy of the options with which the pattern was compiled. The fourth
argument should point to an unsigned long int variable. These option bits
are those specified in the call to pcre_compile(), modified by any
top-level option settings at the start of the pattern itself. In other words,
they are the options that will be in force when matching starts. For example,
if the pattern /(?im)abc(?-i)d/ is compiled with the PCRE_EXTENDED option, the
result is PCRE_CASELESS, PCRE_MULTILINE, and PCRE_EXTENDED.
A pattern is automatically anchored by PCRE if all of its top-level
alternatives begin with one of the following:
^ unless PCRE_MULTILINE is set
\eA always
\eG always
JOIN
.* if PCRE_DOTALL is set and there are no back
references to the subpattern in which .* appears
For such patterns, the PCRE_ANCHORED bit is set in the options returned by
pcre_fullinfo().
PCRE_INFO_RECURSIONLIMIT
If the pattern set a recursion limit by including an item of the form
(*LIMIT_RECURSION=nnnn) at the start, the value is returned. The fourth
argument should point to an unsigned 32-bit integer. If no such value has been
set, the call to pcre_fullinfo() returns the error PCRE_ERROR_UNSET.
PCRE_INFO_SIZE
Return the size of the compiled pattern in bytes (for all three libraries). The
fourth argument should point to a size_t variable. This value does not
include the size of the pcre structure that is returned by
pcre_compile(). The value that is passed as the argument to
pcre_malloc() when pcre_compile() is getting memory in which to
place the compiled data is the value returned by this option plus the size of
the pcre structure. Studying a compiled pattern, with or without JIT,
does not alter the value returned by this option.
PCRE_INFO_STUDYSIZE
Return the size in bytes (for all three libraries) of the data block pointed to
by the study_data field in a pcre_extra block. If pcre_extra
is NULL, or there is no study data, zero is returned. The fourth argument
should point to a size_t variable. The study_data field is set by
pcre_study() to record information that will speed up matching (see the
section entitled
HTML <a href="#studyingapattern">
</a>
"Studying a pattern"
above). The format of the study_data block is private, but its length
is made available via this option so that it can be saved and restored (see the
HREF
pcreprecompile
documentation for details).
PCRE_INFO_REQUIREDCHARFLAGS
Returns 1 if there is a rightmost literal data unit that must exist in any
matched string, other than at its start. The fourth argument should point to
an int variable. If there is no such value, 0 is returned. If returning
1, the character value itself can be retrieved using PCRE_INFO_REQUIREDCHAR.
For anchored patterns, a last literal value is recorded only if it follows something of variable length. For example, for the pattern /^a\ed+z\ed+/ the returned value 1 (with "z" returned from PCRE_INFO_REQUIREDCHAR), but for /^a\edz\ed/ the returned value is 0. PCRE_INFO_REQUIREDCHAR Return the value of the rightmost literal data unit that must exist in any matched string, other than at its start, if such a value has been recorded. The fourth argument should point to an uint32_t variable. If there is no such value, 0 is returned. . .
The pcre_refcount() function is used to maintain a reference count in the data block that contains a compiled pattern. It is provided for the benefit of applications that operate in an object-oriented manner, where different parts of the application may be using the same compiled pattern, but you want to free the block when they are all done.
When a pattern is compiled, the reference count field is initialized to zero. It is changed only by calling this function, whose action is to add the adjust value (which may be positive or negative) to it. The yield of the function is the new value. However, the value of the count is constrained to lie between 0 and 65535, inclusive. If the new value is outside these limits, it is forced to the appropriate limit value.
Except when it is zero, the reference count is not correctly preserved if a pattern is compiled on one host and then transferred to a host whose byte-order is different. (This seems a highly unlikely scenario.) . .
int pcre_exec(const pcre *code, "const pcre_extra *extra," " const char *subject," int length, int startoffset, " int options, int *ovector, int ovecsize);"
The function pcre_exec() is called to match a subject string against a compiled pattern, which is passed in the code argument. If the pattern was studied, the result of the study should be passed in the extra argument. You can call pcre_exec() with the same code and extra arguments as many times as you like, in order to match different subject strings with the same pattern.
This function is the main matching facility of the library, and it operates in
a Perl-like manner. For specialist use there is also an alternative matching
function, which is described
HTML <a href="#dfamatch">
</a>
below
in the section about the pcre_dfa_exec() function.
In most applications, the pattern will have been compiled (and optionally
studied) in the same process that calls pcre_exec(). However, it is
possible to save compiled patterns and study data, and then use them later
in different processes, possibly even on different hosts. For a discussion
about this, see the
HREF
pcreprecompile
documentation.
Here is an example of a simple call to pcre_exec():
int rc;
int ovector[30];
rc = pcre_exec(
re, /* result of pcre_compile() */
NULL, /* we didn't study the pattern */
"some string", /* the subject string */
11, /* the length of the subject string */
0, /* start at offset 0 in the subject */
0, /* default options */
ovector, /* vector of integers for substring information */
30); /* number of elements (NOT size in bytes) */
.
.
HTML <a name="extradata"></a>
The flags field is used to specify which of the other fields are set. The flag bits are: PCRE_EXTRA_CALLOUT_DATA PCRE_EXTRA_EXECUTABLE_JIT PCRE_EXTRA_MARK PCRE_EXTRA_MATCH_LIMIT PCRE_EXTRA_MATCH_LIMIT_RECURSION PCRE_EXTRA_STUDY_DATA PCRE_EXTRA_TABLES Other flag bits should be set to zero. The study_data field and sometimes the executable_jit field are set in the pcre_extra block that is returned by pcre_study(), together with the appropriate flag bits. You should not set these yourself, but you may add to the block by setting other fields and their corresponding flag bits.
The match_limit field provides a means of preventing PCRE from using up a vast amount of resources when running patterns that are not going to match, but which have a very large number of possibilities in their search trees. The classic example is a pattern that uses nested unlimited repeats.
Internally, pcre_exec() uses a function called match(), which it calls repeatedly (sometimes recursively). The limit set by match_limit is imposed on the number of times this function is called during a match, which has the effect of limiting the amount of backtracking that can take place. For patterns that are not anchored, the count restarts from zero for each position in the subject string.
When pcre_exec() is called with a pattern that was successfully studied with a JIT option, the way that the matching is executed is entirely different. However, there is still the possibility of runaway matching that goes on for a very long time, and so the match_limit value is also used in this case (but in a different way) to limit how long the matching can continue.
The default value for the limit can be set when PCRE is built; the default default is 10 million, which handles all but the most extreme cases. You can override the default by suppling pcre_exec() with a pcre_extra block in which match_limit is set, and PCRE_EXTRA_MATCH_LIMIT is set in the flags field. If the limit is exceeded, pcre_exec() returns PCRE_ERROR_MATCHLIMIT.
A value for the match limit may also be supplied by an item at the start of a pattern of the form (*LIMIT_MATCH=d) where d is a decimal number. However, such a setting is ignored unless d is less than the limit set by the caller of pcre_exec() or, if no such limit is set, less than the default.
The match_limit_recursion field is similar to match_limit, but instead of limiting the total number of times that match() is called, it limits the depth of recursion. The recursion depth is a smaller number than the total number of calls, because not all calls to match() are recursive. This limit is of use only if it is set smaller than match_limit.
Limiting the recursion depth limits the amount of machine stack that can be used, or, when PCRE has been compiled to use memory on the heap instead of the stack, the amount of heap memory that can be used. This limit is not relevant, and is ignored, when matching is done using JIT compiled code.
The default value for match_limit_recursion can be set when PCRE is built; the default default is the same value as the default for match_limit. You can override the default by suppling pcre_exec() with a pcre_extra block in which match_limit_recursion is set, and PCRE_EXTRA_MATCH_LIMIT_RECURSION is set in the flags field. If the limit is exceeded, pcre_exec() returns PCRE_ERROR_RECURSIONLIMIT.
A value for the recursion limit may also be supplied by an item at the start of a pattern of the form (*LIMIT_RECURSION=d) where d is a decimal number. However, such a setting is ignored unless d is less than the limit set by the caller of pcre_exec() or, if no such limit is set, less than the default.
The callout_data field is used in conjunction with the "callout" feature,
and is described in the
HREF
pcrecallout
documentation.
The tables field is provided for use with patterns that have been
pre-compiled using custom character tables, saved to disc or elsewhere, and
then reloaded, because the tables that were used to compile a pattern are not
saved with it. See the
HREF
pcreprecompile
documentation for a discussion of saving compiled patterns for later use. If
NULL is passed using this mechanism, it forces PCRE's internal tables to be
used.
Warning: The tables that pcre_exec() uses must be the same as those that were used when the pattern was compiled. If this is not the case, the behaviour of pcre_exec() is undefined. Therefore, when a pattern is compiled and matched in the same process, this field should never be set. In this (the most common) case, the correct table pointer is automatically passed with the compiled pattern from pcre_compile() to pcre_exec().
If PCRE_EXTRA_MARK is set in the flags field, the mark field must
be set to point to a suitable variable. If the pattern contains any
backtracking control verbs such as (*MARK:NAME), and the execution ends up with
a name to pass back, a pointer to the name string (zero terminated) is placed
in the variable pointed to by the mark field. The names are within the
compiled pattern; if you wish to retain such a name you must copy it before
freeing the memory of a compiled pattern. If there is no name to pass back, the
variable pointed to by the mark field is set to NULL. For details of the
backtracking control verbs, see the section entitled
HTML <a href="pcrepattern#backtrackcontrol">
</a>
"Backtracking control"
in the
HREF
pcrepattern
documentation.
.
.
HTML <a name="execoptions"></a>
If the pattern was successfully studied with one of the just-in-time (JIT) compile options, the only supported options for JIT execution are PCRE_NO_UTF8_CHECK, PCRE_NOTBOL, PCRE_NOTEOL, PCRE_NOTEMPTY, PCRE_NOTEMPTY_ATSTART, PCRE_PARTIAL_HARD, and PCRE_PARTIAL_SOFT. If an unsupported option is used, JIT execution is disabled and the normal interpretive code in pcre_exec() is run. PCRE_ANCHORED The PCRE_ANCHORED option limits pcre_exec() to matching at the first matching position. If a pattern was compiled with PCRE_ANCHORED, or turned out to be anchored by virtue of its contents, it cannot be made unachored at matching time. PCRE_BSR_ANYCRLF PCRE_BSR_UNICODE These options (which are mutually exclusive) control what the \eR escape sequence matches. The choice is either to match only CR, LF, or CRLF, or to match any Unicode newline sequence. These options override the choice that was made or defaulted when the pattern was compiled. PCRE_NEWLINE_CR PCRE_NEWLINE_LF PCRE_NEWLINE_CRLF PCRE_NEWLINE_ANYCRLF PCRE_NEWLINE_ANY These options override the newline definition that was chosen or defaulted when the pattern was compiled. For details, see the description of pcre_compile() above. During matching, the newline choice affects the behaviour of the dot, circumflex, and dollar metacharacters. It may also alter the way the match position is advanced after a match failure for an unanchored pattern.
When PCRE_NEWLINE_CRLF, PCRE_NEWLINE_ANYCRLF, or PCRE_NEWLINE_ANY is set, and a match attempt for an unanchored pattern fails when the current position is at a CRLF sequence, and the pattern contains no explicit matches for CR or LF characters, the match position is advanced by two characters instead of one, in other words, to after the CRLF.
The above rule is a compromise that makes the most common cases work as expected. For example, if the pattern is .+A (and the PCRE_DOTALL option is not set), it does not match the string "\er\enA" because, after failing at the start, it skips both the CR and the LF before retrying. However, the pattern [\er\en]A does match that string, because it contains an explicit CR or LF reference, and so advances only by one character after the first failure.
An explicit match for CR of LF is either a literal appearance of one of those characters, or one of the \er or \en escape sequences. Implicit matches such as [^X] do not count, nor does \es (which includes CR and LF in the characters that it matches).
Notwithstanding the above, anomalous effects may still occur when CRLF is a valid newline sequence and explicit \er or \en escapes appear in the pattern. PCRE_NOTBOL This option specifies that first character of the subject string is not the beginning of a line, so the circumflex metacharacter should not match before it. Setting this without PCRE_MULTILINE (at compile time) causes circumflex never to match. This option affects only the behaviour of the circumflex metacharacter. It does not affect \eA. PCRE_NOTEOL This option specifies that the end of the subject string is not the end of a line, so the dollar metacharacter should not match it nor (except in multiline mode) a newline immediately before it. Setting this without PCRE_MULTILINE (at compile time) causes dollar never to match. This option affects only the behaviour of the dollar metacharacter. It does not affect \eZ or \ez. PCRE_NOTEMPTY An empty string is not considered to be a valid match if this option is set. If there are alternatives in the pattern, they are tried. If all the alternatives match the empty string, the entire match fails. For example, if the pattern a?b? is applied to a string not beginning with "a" or "b", it matches an empty string at the start of the subject. With PCRE_NOTEMPTY set, this match is not valid, so PCRE searches further into the string for occurrences of "a" or "b". PCRE_NOTEMPTY_ATSTART This is like PCRE_NOTEMPTY, except that an empty string match that is not at the start of the subject is permitted. If the pattern is anchored, such a match can occur only if the pattern contains \eK.
Perl has no direct equivalent of PCRE_NOTEMPTY or PCRE_NOTEMPTY_ATSTART, but it
does make a special case of a pattern match of the empty string within its
split() function, and when using the /g modifier. It is possible to
emulate Perl's behaviour after matching a null string by first trying the match
again at the same offset with PCRE_NOTEMPTY_ATSTART and PCRE_ANCHORED, and then
if that fails, by advancing the starting offset (see below) and trying an
ordinary match again. There is some code that demonstrates how to do this in
the
HREF
pcredemo
sample program. In the most general case, you have to check to see if the
newline convention recognizes CRLF as a newline, and if so, and the current
character is CR followed by LF, advance the starting offset by two characters
instead of one.
PCRE_NO_START_OPTIMIZE
There are a number of optimizations that pcre_exec() uses at the start of
a match, in order to speed up the process. For example, if it is known that an
unanchored match must start with a specific character, it searches the subject
for that character, and fails immediately if it cannot find it, without
actually running the main matching function. This means that a special item
such as (*COMMIT) at the start of a pattern is not considered until after a
suitable starting point for the match has been found. Also, when callouts or
(*MARK) items are in use, these "start-up" optimizations can cause them to be
skipped if the pattern is never actually used. The start-up optimizations are
in effect a pre-scan of the subject that takes place before the pattern is run.
The PCRE_NO_START_OPTIMIZE option disables the start-up optimizations, possibly causing performance to suffer, but ensuring that in cases where the result is "no match", the callouts do occur, and that items such as (*COMMIT) and (*MARK) are considered at every possible starting position in the subject string. If PCRE_NO_START_OPTIMIZE is set at compile time, it cannot be unset at matching time. The use of PCRE_NO_START_OPTIMIZE at matching time (that is, passing it to pcre_exec()) disables JIT execution; in this situation, matching is always done using interpretively.
Setting PCRE_NO_START_OPTIMIZE can change the outcome of a matching operation.
Consider the pattern
(*COMMIT)ABC
When this is compiled, PCRE records the fact that a match must start with the
character "A". Suppose the subject string is "DEFABC". The start-up
optimization scans along the subject, finds "A" and runs the first match
attempt from there. The (*COMMIT) item means that the pattern must match the
current starting position, which in this case, it does. However, if the same
match is run with PCRE_NO_START_OPTIMIZE set, the initial scan along the
subject string does not happen. The first match attempt is run starting from
"D" and when this fails, (*COMMIT) prevents any further matches being tried, so
the overall result is "no match". If the pattern is studied, more start-up
optimizations may be used. For example, a minimum length for the subject may be
recorded. Consider the pattern
(*MARK:A)(X|Y)
The minimum length for a match is one character. If the subject is "ABC", there
will be attempts to match "ABC", "BC", "C", and then finally an empty string.
If the pattern is studied, the final attempt does not take place, because PCRE
knows that the subject is too short, and so the (*MARK) is never encountered.
In this case, studying the pattern does not affect the overall match result,
which is still "no match", but it does affect the auxiliary information that is
returned.
PCRE_NO_UTF8_CHECK
When PCRE_UTF8 is set at compile time, the validity of the subject as a UTF-8
string is automatically checked when pcre_exec() is subsequently called.
The entire string is checked before any other processing takes place. The value
of startoffset is also checked to ensure that it points to the start of a
UTF-8 character. There is a discussion about the
HTML <a href="pcreunicode.html#utf8strings">
</a>
validity of UTF-8 strings
in the
HREF
pcreunicode
page. If an invalid sequence of bytes is found, pcre_exec() returns the
error PCRE_ERROR_BADUTF8 or, if PCRE_PARTIAL_HARD is set and the problem is a
truncated character at the end of the subject, PCRE_ERROR_SHORTUTF8. In both
cases, information about the precise nature of the error may also be returned
(see the descriptions of these errors in the section entitled Error return
values from pcre_exec()
HTML <a href="#errorlist">
</a>
below).
If startoffset contains a value that does not point to the start of a
UTF-8 character (or to the end of the subject), PCRE_ERROR_BADUTF8_OFFSET is
returned.
If you already know that your subject is valid, and you want to skip these checks for performance reasons, you can set the PCRE_NO_UTF8_CHECK option when calling pcre_exec(). You might want to do this for the second and subsequent calls to pcre_exec() if you are making repeated calls to find all the matches in a single subject string. However, you should be sure that the value of startoffset points to the start of a character (or the end of the subject). When PCRE_NO_UTF8_CHECK is set, the effect of passing an invalid string as a subject or an invalid value of startoffset is undefined. Your program may crash or loop. PCRE_PARTIAL_HARD PCRE_PARTIAL_SOFT These options turn on the partial matching feature. For backwards compatibility, PCRE_PARTIAL is a synonym for PCRE_PARTIAL_SOFT. A partial match occurs if the end of the subject string is reached successfully, but there are not enough subject characters to complete the match. If this happens when PCRE_PARTIAL_SOFT (but not PCRE_PARTIAL_HARD) is set, matching continues by testing any remaining alternatives. Only if no complete match can be found is PCRE_ERROR_PARTIAL returned instead of PCRE_ERROR_NOMATCH. In other words, PCRE_PARTIAL_SOFT says that the caller is prepared to handle a partial match, but only if no complete match can be found.
If PCRE_PARTIAL_HARD is set, it overrides PCRE_PARTIAL_SOFT. In this case, if a partial match is found, pcre_exec() immediately returns PCRE_ERROR_PARTIAL, without considering any other alternatives. In other words, when PCRE_PARTIAL_HARD is set, a partial match is considered to be more important that an alternative complete match.
In both cases, the portion of the string that was inspected when the partial
match was found is set as the first matching string. There is a more detailed
discussion of partial and multi-segment matching, with examples, in the
HREF
pcrepartial
documentation.
.
.
If startoffset is negative or greater than the length of the subject, pcre_exec() returns PCRE_ERROR_BADOFFSET. When the starting offset is zero, the search for a match starts at the beginning of the subject, and this is by far the most common case. In UTF-8 or UTF-16 mode, the offset must point to the start of a character, or the end of the subject (in UTF-32 mode, one data unit equals one character, so all offsets are valid). Unlike the pattern string, the subject may contain binary zeroes.
A non-zero starting offset is useful when searching for another match in the same subject by calling pcre_exec() again after a previous success. Setting startoffset differs from just passing over a shortened string and setting PCRE_NOTBOL in the case of a pattern that begins with any kind of lookbehind. For example, consider the pattern \eBiss\eB which finds occurrences of "iss" in the middle of words. (\eB matches only if the current position in the subject is not a word boundary.) When applied to the string "Mississipi" the first call to pcre_exec() finds the first occurrence. If pcre_exec() is called again with just the remainder of the subject, namely "issipi", it does not match, because \eB is always false at the start of the subject, which is deemed to be a word boundary. However, if pcre_exec() is passed the entire string again, but with startoffset set to 4, it finds the second occurrence of "iss" because it is able to look behind the starting point to discover that it is preceded by a letter.
Finding all the matches in a subject is tricky when the pattern can match an
empty string. It is possible to emulate Perl's /g behaviour by first trying the
match again at the same offset, with the PCRE_NOTEMPTY_ATSTART and
PCRE_ANCHORED options, and then if that fails, advancing the starting offset
and trying an ordinary match again. There is some code that demonstrates how to
do this in the
HREF
pcredemo
sample program. In the most general case, you have to check to see if the
newline convention recognizes CRLF as a newline, and if so, and the current
character is CR followed by LF, advance the starting offset by two characters
instead of one.
If a non-zero starting offset is passed when the pattern is anchored, one attempt to match at the given offset is made. This can only succeed if the pattern does not require the match to be at the start of the subject. . .
Captured substrings are returned to the caller via a vector of integers whose address is passed in ovector. The number of elements in the vector is passed in ovecsize, which must be a non-negative number. Note: this argument is NOT the size of ovector in bytes.
The first two-thirds of the vector is used to pass back captured substrings, each substring using a pair of integers. The remaining third of the vector is used as workspace by pcre_exec() while matching capturing subpatterns, and is not available for passing back information. The number passed in ovecsize should always be a multiple of three. If it is not, it is rounded down.
When a match is successful, information about captured substrings is returned in pairs of integers, starting at the beginning of ovector, and continuing up to two-thirds of its length at the most. The first element of each pair is set to the offset of the first character in a substring, and the second is set to the offset of the first character after the end of a substring. These values are always data unit offsets, even in UTF mode. They are byte offsets in the 8-bit library, 16-bit data item offsets in the 16-bit library, and 32-bit data item offsets in the 32-bit library. Note: they are not character counts.
The first pair of integers, ovector[0] and ovector[1], identify the portion of the subject string matched by the entire pattern. The next pair is used for the first capturing subpattern, and so on. The value returned by pcre_exec() is one more than the highest numbered pair that has been set. For example, if two substrings have been captured, the returned value is 3. If there are no capturing subpatterns, the return value from a successful match is 1, indicating that just the first pair of offsets has been set.
If a capturing subpattern is matched repeatedly, it is the last portion of the string that it matched that is returned.
If the vector is too small to hold all the captured substring offsets, it is used as far as possible (up to two-thirds of its length), and the function returns a value of zero. If neither the actual string matched nor any captured substrings are of interest, pcre_exec() may be called with ovector passed as NULL and ovecsize as zero. However, if the pattern contains back references and the ovector is not big enough to remember the related substrings, PCRE has to get additional memory for use during matching. Thus it is usually advisable to supply an ovector of reasonable size.
There are some cases where zero is returned (indicating vector overflow) when in fact the vector is exactly the right size for the final match. For example, consider the pattern (a)(?:(b)c|bd) If a vector of 6 elements (allowing for only 1 captured substring) is given with subject string "abd", pcre_exec() will try to set the second captured string, thereby recording a vector overflow, before failing to match "c" and backing up to try the second alternative. The zero return, however, does correctly indicate that the maximum number of slots (namely 2) have been filled. In similar cases where there is temporary overflow, but the final number of used slots is actually less than the maximum, a non-zero value is returned.
The pcre_fullinfo() function can be used to find out how many capturing subpatterns there are in a compiled pattern. The smallest size for ovector that will allow for n captured substrings, in addition to the offsets of the substring matched by the whole pattern, is (n+1)*3.
It is possible for capturing subpattern number n+1 to match some part of the subject when subpattern n has not been used at all. For example, if the string "abc" is matched against the pattern (a|(z))(bc) the return from the function is 4, and subpatterns 1 and 3 are matched, but 2 is not. When this happens, both values in the offset pairs corresponding to unused subpatterns are set to -1.
Offset values that correspond to unused subpatterns at the end of the expression are also set to -1. For example, if the string "abc" is matched against the pattern (abc)(x(yz)?)? subpatterns 2 and 3 are not matched. The return from the function is 2, because the highest used capturing subpattern number is 1, and the offsets for for the second and third capturing subpatterns (assuming the vector is large enough, of course) are set to -1.
Note: Elements in the first two-thirds of ovector that do not correspond to capturing parentheses in the pattern are never changed. That is, if a pattern contains n capturing parentheses, no more than ovector[0] to ovector[2n+1] are set by pcre_exec(). The other elements (in the first two-thirds) retain whatever values they previously had.
Some convenience functions are provided for extracting the captured substrings
as separate strings. These are described below.
.
.
HTML <a name="errorlist"></a>
This error is also given if pcre_stack_malloc() fails in
pcre_exec(). This can happen only when PCRE has been compiled with
--disable-stack-for-recursion.
PCRE_ERROR_NOSUBSTRING (-7)
This error is used by the pcre_copy_substring(),
pcre_get_substring(), and pcre_get_substring_list() functions (see
below). It is never returned by pcre_exec().
PCRE_ERROR_MATCHLIMIT (-8)
The backtracking limit, as specified by the match_limit field in a
pcre_extra structure (or defaulted) was reached. See the description
above.
PCRE_ERROR_CALLOUT (-9)
This error is never generated by pcre_exec() itself. It is provided for
use by callout functions that want to yield a distinctive error code. See the
HREF
pcrecallout
documentation for details.
PCRE_ERROR_BADUTF8 (-10)
A string that contains an invalid UTF-8 byte sequence was passed as a subject,
and the PCRE_NO_UTF8_CHECK option was not set. If the size of the output vector
(ovecsize) is at least 2, the byte offset to the start of the the invalid
UTF-8 character is placed in the first element, and a reason code is placed in
the second element. The reason codes are listed in the
HTML <a href="#badutf8reasons">
</a>
following section.
For backward compatibility, if PCRE_PARTIAL_HARD is set and the problem is a
truncated UTF-8 character at the end of the subject (reason codes 1 to 5),
PCRE_ERROR_SHORTUTF8 is returned instead of PCRE_ERROR_BADUTF8.
PCRE_ERROR_BADUTF8_OFFSET (-11)
The UTF-8 byte sequence that was passed as a subject was checked and found to
be valid (the PCRE_NO_UTF8_CHECK option was not set), but the value of
startoffset did not point to the beginning of a UTF-8 character or the
end of the subject.
PCRE_ERROR_PARTIAL (-12)
The subject string did not match, but it did match partially. See the
HREF
pcrepartial
documentation for details of partial matching.
PCRE_ERROR_BADPARTIAL (-13)
This code is no longer in use. It was formerly returned when the PCRE_PARTIAL
option was used with a compiled pattern containing items that were not
supported for partial matching. From release 8.00 onwards, there are no
restrictions on partial matching.
PCRE_ERROR_INTERNAL (-14)
An unexpected internal error has occurred. This error could be caused by a bug
in PCRE or by overwriting of the compiled pattern.
PCRE_ERROR_BADCOUNT (-15)
This error is given if the value of the ovecsize argument is negative.
PCRE_ERROR_RECURSIONLIMIT (-21)
The internal recursion limit, as specified by the match_limit_recursion
field in a pcre_extra structure (or defaulted) was reached. See the
description above.
PCRE_ERROR_BADNEWLINE (-23)
An invalid combination of PCRE_NEWLINE_xxx options was given.
PCRE_ERROR_BADOFFSET (-24)
The value of startoffset was negative or greater than the length of the
subject, that is, the value in length.
PCRE_ERROR_SHORTUTF8 (-25)
This error is returned instead of PCRE_ERROR_BADUTF8 when the subject string
ends with a truncated UTF-8 character and the PCRE_PARTIAL_HARD option is set.
Information about the failure is returned as for PCRE_ERROR_BADUTF8. It is in
fact sufficient to detect this case, but this special error code for
PCRE_PARTIAL_HARD precedes the implementation of returned information; it is
retained for backwards compatibility.
PCRE_ERROR_RECURSELOOP (-26)
This error is returned when pcre_exec() detects a recursion loop within
the pattern. Specifically, it means that either the whole pattern or a
subpattern has been called recursively for the second time at the same position
in the subject string. Some simple patterns that might do this are detected and
faulted at compile time, but more complicated cases, in particular mutual
recursions between two different subpatterns, cannot be detected until run
time.
PCRE_ERROR_JIT_STACKLIMIT (-27)
This error is returned when a pattern that was successfully studied using a
JIT compile option is being matched, but the memory available for the
just-in-time processing stack is not large enough. See the
HREF
pcrejit
documentation for more details.
PCRE_ERROR_BADMODE (-28)
This error is given if a pattern that was compiled by the 8-bit library is
passed to a 16-bit or 32-bit library function, or vice versa.
PCRE_ERROR_BADENDIANNESS (-29)
This error is given if a pattern that was compiled and saved is reloaded on a
host with different endianness. The utility function
pcre_pattern_to_host_byte_order() can be used to convert such a pattern
so that it runs on the new host.
PCRE_ERROR_JIT_BADOPTION
This error is returned when a pattern that was successfully studied using a JIT
compile option is being matched, but the matching mode (partial or complete
match) does not correspond to any JIT compilation mode. When the JIT fast path
function is used, this error may be also given for invalid options. See the
HREF
pcrejit
documentation for more details.
PCRE_ERROR_BADLENGTH (-32)
This error is given if pcre_exec() is called with a negative value for
the length argument.
Error numbers -16 to -20, -22, and 30 are not used by pcre_exec().
.
.
HTML <a name="badutf8reasons"></a>
pcre16
and HREF
pcre32
pages.
When pcre_exec() returns either PCRE_ERROR_BADUTF8 or PCRE_ERROR_SHORTUTF8, and the size of the output vector (ovecsize) is at least 2, the offset of the start of the invalid UTF-8 character is placed in the first output vector element (ovector[0]) and a reason code is placed in the second element (ovector[1]). The reason codes are given names in the pcre.h header file: PCRE_UTF8_ERR1 PCRE_UTF8_ERR2 PCRE_UTF8_ERR3 PCRE_UTF8_ERR4 PCRE_UTF8_ERR5 The string ends with a truncated UTF-8 character; the code specifies how many bytes are missing (1 to 5). Although RFC 3629 restricts UTF-8 characters to be no longer than 4 bytes, the encoding scheme (originally defined by RFC 2279) allows for up to 6 bytes, and this is checked first; hence the possibility of 4 or 5 missing bytes. PCRE_UTF8_ERR6 PCRE_UTF8_ERR7 PCRE_UTF8_ERR8 PCRE_UTF8_ERR9 PCRE_UTF8_ERR10 The two most significant bits of the 2nd, 3rd, 4th, 5th, or 6th byte of the character do not have the binary value 0b10 (that is, either the most significant bit is 0, or the next bit is 1). PCRE_UTF8_ERR11 PCRE_UTF8_ERR12 A character that is valid by the RFC 2279 rules is either 5 or 6 bytes long; these code points are excluded by RFC 3629. PCRE_UTF8_ERR13 A 4-byte character has a value greater than 0x10fff; these code points are excluded by RFC 3629. PCRE_UTF8_ERR14 A 3-byte character has a value in the range 0xd800 to 0xdfff; this range of code points are reserved by RFC 3629 for use with UTF-16, and so are excluded from UTF-8. PCRE_UTF8_ERR15 PCRE_UTF8_ERR16 PCRE_UTF8_ERR17 PCRE_UTF8_ERR18 PCRE_UTF8_ERR19 A 2-, 3-, 4-, 5-, or 6-byte character is "overlong", that is, it codes for a value that can be represented by fewer bytes, which is invalid. For example, the two bytes 0xc0, 0xae give the value 0x2e, whose correct coding uses just one byte. PCRE_UTF8_ERR20 The two most significant bits of the first byte of a character have the binary value 0b10 (that is, the most significant bit is 1 and the second is 0). Such a byte can only validly occur as the second or subsequent byte of a multi-byte character. PCRE_UTF8_ERR21 The first byte of a character has the value 0xfe or 0xff. These values can never occur in a valid UTF-8 string. PCRE_UTF8_ERR22 This error code was formerly used when the presence of a so-called "non-character" caused an error. Unicode corrigendum #9 makes it clear that such characters should not cause a string to be rejected, and so this code is no longer in use and is never returned. . .
int pcre_copy_substring(const char *subject, int *ovector, " int stringcount, int stringnumber, char *buffer," " int buffersize);" int pcre_get_substring(const char *subject, int *ovector, " int stringcount, int stringnumber," " const char **stringptr);" int pcre_get_substring_list(const char *subject, " int *ovector, int stringcount, const char ***listptr);"
Captured substrings can be accessed directly by using the offsets returned by pcre_exec() in ovector. For convenience, the functions pcre_copy_substring(), pcre_get_substring(), and pcre_get_substring_list() are provided for extracting captured substrings as new, separate, zero-terminated strings. These functions identify substrings by number. The next section describes functions for extracting named substrings.
A substring that contains a binary zero is correctly extracted and has a further zero added on the end, but the result is not, of course, a C string. However, you can process such a string by referring to the length that is returned by pcre_copy_substring() and pcre_get_substring(). Unfortunately, the interface to pcre_get_substring_list() is not adequate for handling strings containing binary zeros, because the end of the final string is not independently indicated.
The first three arguments are the same for all three of these functions: subject is the subject string that has just been successfully matched, ovector is a pointer to the vector of integer offsets that was passed to pcre_exec(), and stringcount is the number of substrings that were captured by the match, including the substring that matched the entire regular expression. This is the value returned by pcre_exec() if it is greater than zero. If pcre_exec() returned zero, indicating that it ran out of space in ovector, the value passed as stringcount should be the number of elements in the vector divided by three.
The functions pcre_copy_substring() and pcre_get_substring() extract a single substring, whose number is given as stringnumber. A value of zero extracts the substring that matched the entire pattern, whereas higher values extract the captured substrings. For pcre_copy_substring(), the string is placed in buffer, whose length is given by buffersize, while for pcre_get_substring() a new block of memory is obtained via pcre_malloc, and its address is returned via stringptr. The yield of the function is the length of the string, not including the terminating zero, or one of these error codes: PCRE_ERROR_NOMEMORY (-6) The buffer was too small for pcre_copy_substring(), or the attempt to get memory failed for pcre_get_substring(). PCRE_ERROR_NOSUBSTRING (-7) There is no substring whose number is stringnumber.
The pcre_get_substring_list() function extracts all available substrings and builds a list of pointers to them. All this is done in a single block of memory that is obtained via pcre_malloc. The address of the memory block is returned via listptr, which is also the start of the list of string pointers. The end of the list is marked by a NULL pointer. The yield of the function is zero if all went well, or the error code PCRE_ERROR_NOMEMORY (-6) if the attempt to get the memory block failed.
When any of these functions encounter a substring that is unset, which can happen when capturing subpattern number n+1 matches some part of the subject, but subpattern n has not been used at all, they return an empty string. This can be distinguished from a genuine zero-length substring by inspecting the appropriate offset in ovector, which is negative for unset substrings.
The two convenience functions pcre_free_substring() and pcre_free_substring_list() can be used to free the memory returned by a previous call of pcre_get_substring() or pcre_get_substring_list(), respectively. They do nothing more than call the function pointed to by pcre_free, which of course could be called directly from a C program. However, PCRE is used in some situations where it is linked via a special interface to another programming language that cannot use pcre_free directly; it is for these cases that the functions are provided. . .
int pcre_get_stringnumber(const pcre *code, " const char *name);" int pcre_copy_named_substring(const pcre *code, " const char *subject, int *ovector," " int stringcount, const char *stringname," " char *buffer, int buffersize);" int pcre_get_named_substring(const pcre *code, " const char *subject, int *ovector," " int stringcount, const char *stringname," " const char **stringptr);"
To extract a substring by name, you first have to find associated number. For example, for this pattern (a+)b(?<xxx>\ed+)... the number of the subpattern called "xxx" is 2. If the name is known to be unique (PCRE_DUPNAMES was not set), you can find the number from the name by calling pcre_get_stringnumber(). The first argument is the compiled pattern, and the second is the name. The yield of the function is the subpattern number, or PCRE_ERROR_NOSUBSTRING (-7) if there is no subpattern of that name.
Given the number, you can extract the substring directly, or use one of the functions described in the previous section. For convenience, there are also two functions that do the whole job.
Most of the arguments of pcre_copy_named_substring() and pcre_get_named_substring() are the same as those for the similarly named functions that extract by number. As these are described in the previous section, they are not re-described here. There are just two differences:
First, instead of a substring number, a substring name is given. Second, there is an extra argument, given at the start, which is a pointer to the compiled pattern. This is needed in order to gain access to the name-to-number translation table.
These functions call pcre_get_stringnumber(), and if it succeeds, they then call pcre_copy_substring() or pcre_get_substring(), as appropriate. NOTE: If PCRE_DUPNAMES is set and there are duplicate names, the behaviour may not be what you want (see the next section).
Warning: If the pattern uses the (?| feature to set up multiple
subpatterns with the same number, as described in the
HTML <a href="pcrepattern.html#dupsubpatternnumber">
</a>
section on duplicate subpattern numbers
in the
HREF
pcrepattern
page, you cannot use names to distinguish the different subpatterns, because
names are not included in the compiled code. The matching process uses only
numbers. For this reason, the use of different names for subpatterns of the
same number causes an error at compile time.
.
.
int pcre_get_stringtable_entries(const pcre *code, " const char *name, char **first, char **last);"
When a pattern is compiled with the PCRE_DUPNAMES option, names for subpatterns are not required to be unique. (Duplicate names are always allowed for subpatterns with the same number, created by using the (?| feature. Indeed, if such subpatterns are named, they are required to use the same names.)
Normally, patterns with duplicate names are such that in any one match, only
one of the named subpatterns participates. An example is shown in the
HREF
pcrepattern
documentation.
When duplicates are present, pcre_copy_named_substring() and pcre_get_named_substring() return the first substring corresponding to the given name that is set. If none are set, PCRE_ERROR_NOSUBSTRING (-7) is returned; no data is returned. The pcre_get_stringnumber() function returns one of the numbers that are associated with the name, but it is not defined which it is.
If you want to get full details of all captured substrings for a given name,
you must use the pcre_get_stringtable_entries() function. The first
argument is the compiled pattern, and the second is the name. The third and
fourth are pointers to variables which are updated by the function. After it
has run, they point to the first and last entries in the name-to-number table
for the given name. The function itself returns the length of each entry, or
PCRE_ERROR_NOSUBSTRING (-7) if there are none. The format of the table is
described above in the section entitled Information about a pattern
HTML <a href="#infoaboutpattern">
</a>
above.
Given all the relevant entries for the name, you can extract each of their
numbers, and hence the captured data, if any.
.
.
pcrecallout
documentation.
What you have to do is to insert a callout right at the end of the pattern. When your callout function is called, extract and save the current matched substring. Then return 1, which forces pcre_exec() to backtrack and try other alternatives. Ultimately, when it runs out of matches, pcre_exec() will yield PCRE_ERROR_NOMATCH. . .
pcrestack
documentation. The estimate that is output by pcretest when called with the -m and -C options is obtained by calling pcre_exec with the values NULL, NULL, NULL, -999, and -999 for its first five arguments.
Normally, if its first argument is NULL, pcre_exec() immediately returns the negative error code PCRE_ERROR_NULL, but with this special combination of arguments, it returns instead a negative number whose absolute value is the approximate stack frame size in bytes. (A negative number is used so that it is clear that no match has happened.) The value is approximate because in some cases, recursive calls to pcre_exec() occur when there are one or two additional variables on the stack.
If PCRE has been compiled to use the heap instead of the stack for recursion,
the value returned is the size of each block that is obtained from the heap.
.
.
HTML <a name="dfamatch"></a>
int pcre_dfa_exec(const pcre *code, "const pcre_extra *extra," " const char *subject, int length, int startoffset," " int options, int *ovector, int ovecsize," " int *workspace, int wscount);"
The function pcre_dfa_exec() is called to match a subject string against
a compiled pattern, using a matching algorithm that scans the subject string
just once, and does not backtrack. This has different characteristics to the
normal algorithm, and is not compatible with Perl. Some of the features of PCRE
patterns are not supported. Nevertheless, there are times when this kind of
matching can be useful. For a discussion of the two matching algorithms, and a
list of features that pcre_dfa_exec() does not support, see the
HREF
pcrematching
documentation.
The arguments for the pcre_dfa_exec() function are the same as for pcre_exec(), plus two extras. The ovector argument is used in a different way, and this is described below. The other common arguments are used in the same way as for pcre_exec(), so their description is not repeated here.
The two additional arguments provide workspace for the function. The workspace vector should contain at least 20 elements. It is used for keeping track of multiple paths through the pattern tree. More workspace will be needed for patterns and subjects where there are a lot of potential matches.
Here is an example of a simple call to pcre_dfa_exec(): int rc; int ovector[10]; int wspace[20]; rc = pcre_dfa_exec( re, /* result of pcre_compile() */ NULL, /* we didn't study the pattern */ "some string", /* the subject string */ 11, /* the length of the subject string */ 0, /* start at offset 0 in the subject */ 0, /* default options */ ovector, /* vector of integers for substring information */ 10, /* number of elements (NOT size in bytes) */ wspace, /* working space vector */ 20); /* number of elements (NOT size in bytes) */ .
pcrepartial
documentation. PCRE_DFA_SHORTEST Setting the PCRE_DFA_SHORTEST option causes the matching algorithm to stop as soon as it has found one match. Because of the way the alternative algorithm works, this is necessarily the shortest possible match at the first possible matching point in the subject string. PCRE_DFA_RESTART When pcre_dfa_exec() returns a partial match, it is possible to call it again, with additional subject characters, and have it continue with the same match. The PCRE_DFA_RESTART option requests this action; when it is set, the workspace and wscount options must reference the same vector as before because data about the match so far is left in them after a partial match. There is more discussion of this facility in the HREF
pcrepartial
documentation. . .
The strings are returned in reverse order of length; that is, the longest matching string is given first. If there were too many matches to fit into ovector, the yield of the function is zero, and the vector is filled with the longest matches. Unlike pcre_exec(), pcre_dfa_exec() can use the entire ovector for returning matched strings.
NOTE: PCRE's "auto-possessification" optimization usually applies to character repeats at the end of a pattern (as well as internally). For example, the pattern "a\ed+" is compiled as if it were "a\ed++" because there is no point even considering the possibility of backtracking into the repeated digits. For DFA matching, this means that only one possible match is found. If you really do want multiple matches in such cases, either use an ungreedy repeat ("a\ed+?") or set the PCRE_NO_AUTO_POSSESS option when compiling. . .
</a>
above.
There are in addition the following errors that are specific to pcre_dfa_exec(): PCRE_ERROR_DFA_UITEM (-16) This return is given if pcre_dfa_exec() encounters an item in the pattern that it does not support, for instance, the use of \eC or a back reference. PCRE_ERROR_DFA_UCOND (-17) This return is given if pcre_dfa_exec() encounters a condition item that uses a back reference for the condition, or a test for recursion in a specific group. These are not supported. PCRE_ERROR_DFA_UMLIMIT (-18) This return is given if pcre_dfa_exec() is called with an extra block that contains a setting of the match_limit or match_limit_recursion fields. This is not supported (these fields are meaningless for DFA matching). PCRE_ERROR_DFA_WSSIZE (-19) This return is given if pcre_dfa_exec() runs out of space in the workspace vector. PCRE_ERROR_DFA_RECURSE (-20) When a recursive subpattern is processed, the matching function calls itself recursively, using private vectors for ovector and workspace. This error is given if the output vector is not large enough. This should be extremely rare, as a vector of size 1000 is used. PCRE_ERROR_DFA_BADRESTART (-30) When pcre_dfa_exec() is called with the PCRE_DFA_RESTART option, some plausibility checks are made on the contents of the workspace, which should contain data about the previous partial match. If any of these checks fail, this error is given. . .
Philip Hazel University Computing Service Cambridge CB2 3QH, England.. .
Last updated: 09 February 2014 Copyright (c) 1997-2014 University of Cambridge.
