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-
-This page is part of the PCRE HTML documentation. It was generated automatically
-from the original man page. If there is any nonsense in it, please consult the
-man page, in case the conversion went wrong.
-
-#include <pcreposix.h>
-
-int regcomp(regex_t *preg, const char *pattern,
- int cflags);
-
-This set of functions provides a POSIX-style API for the PCRE regular
-expression 8-bit library. See the
-pcreapi
-documentation for a description of PCRE's native API, which contains much
-additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit
-and 32-bit library.
-
-The functions described here are just wrapper functions that ultimately call
-the PCRE native API. Their prototypes are defined in the pcreposix.h
-header file, and on Unix systems the library itself is called
-pcreposix.a, so can be accessed by adding -lpcreposix to the
-command for linking an application that uses them. Because the POSIX functions
-call the native ones, it is also necessary to add -lpcre.
-
-I have implemented only those POSIX option bits that can be reasonably mapped
-to PCRE native options. In addition, the option REG_EXTENDED is defined with
-the value zero. This has no effect, but since programs that are written to the
-POSIX interface often use it, this makes it easier to slot in PCRE as a
-replacement library. Other POSIX options are not even defined.
-
-There are also some other options that are not defined by POSIX. These have
-been added at the request of users who want to make use of certain
-PCRE-specific features via the POSIX calling interface.
-
-When PCRE is called via these functions, it is only the API that is POSIX-like
-in style. The syntax and semantics of the regular expressions themselves are
-still those of Perl, subject to the setting of various PCRE options, as
-described below. "POSIX-like in style" means that the API approximates to the
-POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
-domains it is probably even less compatible.
-
-The header for these functions is supplied as pcreposix.h to avoid any
-potential clash with other POSIX libraries. It can, of course, be renamed or
-aliased as regex.h, which is the "correct" name. It provides two
-structure types, regex_t for compiled internal forms, and
-regmatch_t for returning captured substrings. It also defines some
-constants whose names start with "REG_"; these are used for setting options and
-identifying error codes.
-
-The function regcomp() is called to compile a pattern into an
-internal form. The pattern is a C string terminated by a binary zero, and
-is passed in the argument pattern. The preg argument is a pointer
-to a regex_t structure that is used as a base for storing information
-about the compiled regular expression.
-
-The argument cflags is either zero, or contains one or more of the bits
-defined by the following macros:
-pcreposix man page
-
-
-
-
SYNOPSIS
-
-
-int regexec(regex_t *preg, const char *string,
- size_t nmatch, regmatch_t pmatch[], int eflags);
- size_t regerror(int errcode, const regex_t *preg,
- char *errbuf, size_t errbuf_size);
-
-
-void regfree(regex_t *preg);
-
DESCRIPTION
-
COMPILING A PATTERN
-
- REG_DOTALL
-
-The PCRE_DOTALL option is set when the regular expression is passed for
-compilation to the native function. Note that REG_DOTALL is not part of the
-POSIX standard.
-
- REG_ICASE
-
-The PCRE_CASELESS option is set when the regular expression is passed for
-compilation to the native function.
-
- REG_NEWLINE
-
-The PCRE_MULTILINE option is set when the regular expression is passed for
-compilation to the native function. Note that this does not mimic the
-defined POSIX behaviour for REG_NEWLINE (see the following section).
-
- REG_NOSUB
-
-The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
-for compilation to the native function. In addition, when a pattern that is
-compiled with this flag is passed to regexec() for matching, the
-nmatch and pmatch arguments are ignored, and no captured strings
-are returned.
-
- REG_UCP
-
-The PCRE_UCP option is set when the regular expression is passed for
-compilation to the native function. This causes PCRE to use Unicode properties
-when matchine \d, \w, etc., instead of just recognizing ASCII values. Note
-that REG_UTF8 is not part of the POSIX standard.
-
- REG_UNGREEDY
-
-The PCRE_UNGREEDY option is set when the regular expression is passed for
-compilation to the native function. Note that REG_UNGREEDY is not part of the
-POSIX standard.
-
- REG_UTF8
-
-The PCRE_UTF8 option is set when the regular expression is passed for
-compilation to the native function. This causes the pattern itself and all data
-strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
-is not part of the POSIX standard.
-
-In the absence of these flags, no options are passed to the native function. -This means the the regex is compiled with PCRE default semantics. In -particular, the way it handles newline characters in the subject string is the -Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only -some of the effects specified for REG_NEWLINE. It does not affect the way -newlines are matched by . (they are not) or by a negative class such as [^a] -(they are). -
--The yield of regcomp() is zero on success, and non-zero otherwise. The -preg structure is filled in on success, and one member of the structure -is public: re_nsub contains the number of capturing subpatterns in -the regular expression. Various error codes are defined in the header file. -
--NOTE: If the yield of regcomp() is non-zero, you must not attempt to -use the contents of the preg structure. If, for example, you pass it to -regexec(), the result is undefined and your program is likely to crash. -
--This area is not simple, because POSIX and Perl take different views of things. -It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never -intended to be a POSIX engine. The following table lists the different -possibilities for matching newline characters in PCRE: -
- Default Change with - - . matches newline no PCRE_DOTALL - newline matches [^a] yes not changeable - $ matches \n at end yes PCRE_DOLLARENDONLY - $ matches \n in middle no PCRE_MULTILINE - ^ matches \n in middle no PCRE_MULTILINE --This is the equivalent table for POSIX: -
- Default Change with - - . matches newline yes REG_NEWLINE - newline matches [^a] yes REG_NEWLINE - $ matches \n at end no REG_NEWLINE - $ matches \n in middle no REG_NEWLINE - ^ matches \n in middle no REG_NEWLINE --PCRE's behaviour is the same as Perl's, except that there is no equivalent for -PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop -newline from matching [^a]. - -
-The default POSIX newline handling can be obtained by setting PCRE_DOTALL and -PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the -REG_NEWLINE action. -
--The function regexec() is called to match a compiled pattern preg -against a given string, which is by default terminated by a zero byte -(but see REG_STARTEND below), subject to the options in eflags. These can -be: -
- REG_NOTBOL --The PCRE_NOTBOL option is set when calling the underlying PCRE matching -function. -
- REG_NOTEMPTY --The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching -function. Note that REG_NOTEMPTY is not part of the POSIX standard. However, -setting this option can give more POSIX-like behaviour in some situations. -
- REG_NOTEOL --The PCRE_NOTEOL option is set when calling the underlying PCRE matching -function. -
- REG_STARTEND --The string is considered to start at string + pmatch[0].rm_so and -to have a terminating NUL located at string + pmatch[0].rm_eo -(there need not actually be a NUL at that location), regardless of the value of -nmatch. This is a BSD extension, compatible with but not specified by -IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software -intended to be portable to other systems. Note that a non-zero rm_so does -not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not -how it is matched. - -
-If the pattern was compiled with the REG_NOSUB flag, no data about any matched -strings is returned. The nmatch and pmatch arguments of -regexec() are ignored. -
--If the value of nmatch is zero, or if the value pmatch is NULL, -no data about any matched strings is returned. -
--Otherwise,the portion of the string that was matched, and also any captured -substrings, are returned via the pmatch argument, which points to an -array of nmatch structures of type regmatch_t, containing the -members rm_so and rm_eo. These contain the offset to the first -character of each substring and the offset to the first character after the end -of each substring, respectively. The 0th element of the vector relates to the -entire portion of string that was matched; subsequent elements relate to -the capturing subpatterns of the regular expression. Unused entries in the -array have both structure members set to -1. -
--A successful match yields a zero return; various error codes are defined in the -header file, of which REG_NOMATCH is the "expected" failure code. -
--The regerror() function maps a non-zero errorcode from either -regcomp() or regexec() to a printable message. If preg is not -NULL, the error should have arisen from the use of that structure. A message -terminated by a binary zero is placed in errbuf. The length of the -message, including the zero, is limited to errbuf_size. The yield of the -function is the size of buffer needed to hold the whole message. -
--Compiling a regular expression causes memory to be allocated and associated -with the preg structure. The function regfree() frees all such -memory, after which preg may no longer be used as a compiled expression. -
-
-Philip Hazel
-
-University Computing Service
-
-Cambridge CB2 3QH, England.
-
-
-Last updated: 09 January 2012
-
-Copyright © 1997-2012 University of Cambridge.
-
-
-Return to the PCRE index page. -
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