From 844c971d8aeb2693bc01739963f5da675b989d03 Mon Sep 17 00:00:00 2001
From: Kirill Volinsky
+Return to the PCRE index page.
+
+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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