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<html> |
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<head> |
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<title>pcreposix specification</title> |
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<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB"> |
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<h1>pcreposix man page</h1> |
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<p> |
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Return to the <a href="index.html">PCRE index page</a>. |
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</p> |
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<p> |
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This page is part of the PCRE HTML documentation. It was generated automatically |
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from the original man page. If there is any nonsense in it, please consult the |
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man page, in case the conversion went wrong. |
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<br> |
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<ul> |
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<li><a name="TOC1" href="#SEC1">SYNOPSIS OF POSIX API</a> |
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<li><a name="TOC2" href="#SEC2">DESCRIPTION</a> |
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<li><a name="TOC3" href="#SEC3">COMPILING A PATTERN</a> |
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<li><a name="TOC4" href="#SEC4">MATCHING NEWLINE CHARACTERS</a> |
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<li><a name="TOC5" href="#SEC5">MATCHING A PATTERN</a> |
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<li><a name="TOC6" href="#SEC6">ERROR MESSAGES</a> |
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<li><a name="TOC7" href="#SEC7">MEMORY USAGE</a> |
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<li><a name="TOC8" href="#SEC8">AUTHOR</a> |
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</ul> |
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<br><a name="SEC1" href="#TOC1">SYNOPSIS OF POSIX API</a><br> |
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<P> |
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<b>#include <pcreposix.h></b> |
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</P> |
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<P> |
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<b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b> |
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<b>int <i>cflags</i>);</b> |
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</P> |
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<P> |
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<b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b> |
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<b>size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>[], int <i>eflags</i>);</b> |
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</P> |
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<P> |
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<b>size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b> |
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<b>char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b> |
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</P> |
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<P> |
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<b>void regfree(regex_t *<i>preg</i>);</b> |
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</P> |
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<br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br> |
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<P> |
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This set of functions provides a POSIX-style API to the PCRE regular expression |
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package. See the |
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<a href="pcreapi.html"><b>pcreapi</b></a> |
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documentation for a description of PCRE's native API, which contains much |
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additional functionality. |
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</P> |
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<P> |
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The functions described here are just wrapper functions that ultimately call |
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the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b> |
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header file, and on Unix systems the library itself is called |
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<b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the |
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command for linking an application that uses them. Because the POSIX functions |
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call the native ones, it is also necessary to add <b>-lpcre</b>. |
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</P> |
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<P> |
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I have implemented only those option bits that can be reasonably mapped to PCRE |
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native options. In addition, the option REG_EXTENDED is defined with the value |
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zero. This has no effect, but since programs that are written to the POSIX |
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interface often use it, this makes it easier to slot in PCRE as a replacement |
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library. Other POSIX options are not even defined. |
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</P> |
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<P> |
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When PCRE is called via these functions, it is only the API that is POSIX-like |
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in style. The syntax and semantics of the regular expressions themselves are |
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still those of Perl, subject to the setting of various PCRE options, as |
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described below. "POSIX-like in style" means that the API approximates to the |
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POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding |
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domains it is probably even less compatible. |
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</P> |
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<P> |
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The header for these functions is supplied as <b>pcreposix.h</b> to avoid any |
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potential clash with other POSIX libraries. It can, of course, be renamed or |
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aliased as <b>regex.h</b>, which is the "correct" name. It provides two |
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structure types, <i>regex_t</i> for compiled internal forms, and |
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<i>regmatch_t</i> for returning captured substrings. It also defines some |
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constants whose names start with "REG_"; these are used for setting options and |
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identifying error codes. |
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</P> |
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<P> |
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</P> |
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<br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br> |
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<P> |
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The function <b>regcomp()</b> is called to compile a pattern into an |
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internal form. The pattern is a C string terminated by a binary zero, and |
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is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer |
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to a <b>regex_t</b> structure that is used as a base for storing information |
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about the compiled regular expression. |
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</P> |
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<P> |
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The argument <i>cflags</i> is either zero, or contains one or more of the bits |
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defined by the following macros: |
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<pre> |
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REG_DOTALL |
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</pre> |
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The PCRE_DOTALL option is set when the regular expression is passed for |
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compilation to the native function. Note that REG_DOTALL is not part of the |
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POSIX standard. |
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<pre> |
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REG_ICASE |
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</pre> |
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The PCRE_CASELESS option is set when the regular expression is passed for |
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compilation to the native function. |
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<pre> |
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REG_NEWLINE |
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</pre> |
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The PCRE_MULTILINE option is set when the regular expression is passed for |
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compilation to the native function. Note that this does <i>not</i> mimic the |
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defined POSIX behaviour for REG_NEWLINE (see the following section). |
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<pre> |
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REG_NOSUB |
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</pre> |
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The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed |
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for compilation to the native function. In addition, when a pattern that is |
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compiled with this flag is passed to <b>regexec()</b> for matching, the |
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<i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings |
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are returned. |
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<pre> |
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REG_UTF8 |
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</pre> |
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The PCRE_UTF8 option is set when the regular expression is passed for |
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compilation to the native function. This causes the pattern itself and all data |
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strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8 |
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is not part of the POSIX standard. |
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</P> |
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<P> |
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In the absence of these flags, no options are passed to the native function. |
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This means the the regex is compiled with PCRE default semantics. In |
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particular, the way it handles newline characters in the subject string is the |
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Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only |
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<i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way |
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newlines are matched by . (they aren't) or by a negative class such as [^a] |
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(they are). |
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</P> |
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<P> |
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The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The |
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<i>preg</i> structure is filled in on success, and one member of the structure |
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is public: <i>re_nsub</i> contains the number of capturing subpatterns in |
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the regular expression. Various error codes are defined in the header file. |
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</P> |
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<br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br> |
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<P> |
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This area is not simple, because POSIX and Perl take different views of things. |
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It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never |
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intended to be a POSIX engine. The following table lists the different |
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possibilities for matching newline characters in PCRE: |
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<pre> |
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Default Change with |
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. matches newline no PCRE_DOTALL |
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newline matches [^a] yes not changeable |
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$ matches \n at end yes PCRE_DOLLARENDONLY |
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$ matches \n in middle no PCRE_MULTILINE |
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^ matches \n in middle no PCRE_MULTILINE |
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</pre> |
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This is the equivalent table for POSIX: |
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<pre> |
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Default Change with |
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. matches newline yes REG_NEWLINE |
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newline matches [^a] yes REG_NEWLINE |
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$ matches \n at end no REG_NEWLINE |
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$ matches \n in middle no REG_NEWLINE |
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^ matches \n in middle no REG_NEWLINE |
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</pre> |
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PCRE's behaviour is the same as Perl's, except that there is no equivalent for |
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PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop |
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newline from matching [^a]. |
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</P> |
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<P> |
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The default POSIX newline handling can be obtained by setting PCRE_DOTALL and |
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PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the |
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REG_NEWLINE action. |
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</P> |
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<br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br> |
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<P> |
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The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i> |
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against a given <i>string</i>, which is terminated by a zero byte, subject to |
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the options in <i>eflags</i>. These can be: |
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<pre> |
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REG_NOTBOL |
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</pre> |
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The PCRE_NOTBOL option is set when calling the underlying PCRE matching |
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function. |
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<pre> |
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REG_NOTEOL |
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</pre> |
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The PCRE_NOTEOL option is set when calling the underlying PCRE matching |
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function. |
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</P> |
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<P> |
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If the pattern was compiled with the REG_NOSUB flag, no data about any matched |
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strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of |
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<b>regexec()</b> are ignored. |
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</P> |
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<P> |
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Otherwise,the portion of the string that was matched, and also any captured |
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substrings, are returned via the <i>pmatch</i> argument, which points to an |
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array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the |
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members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first |
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character of each substring and the offset to the first character after the end |
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of each substring, respectively. The 0th element of the vector relates to the |
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entire portion of <i>string</i> that was matched; subsequent elements relate to |
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the capturing subpatterns of the regular expression. Unused entries in the |
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array have both structure members set to -1. |
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</P> |
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<P> |
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A successful match yields a zero return; various error codes are defined in the |
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header file, of which REG_NOMATCH is the "expected" failure code. |
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</P> |
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<br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br> |
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<P> |
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The <b>regerror()</b> function maps a non-zero errorcode from either |
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<b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not |
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NULL, the error should have arisen from the use of that structure. A message |
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terminated by a binary zero is placed in <i>errbuf</i>. The length of the |
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message, including the zero, is limited to <i>errbuf_size</i>. The yield of the |
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function is the size of buffer needed to hold the whole message. |
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</P> |
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<br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br> |
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<P> |
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Compiling a regular expression causes memory to be allocated and associated |
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with the <i>preg</i> structure. The function <b>regfree()</b> frees all such |
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memory, after which <i>preg</i> may no longer be used as a compiled expression. |
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</P> |
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<br><a name="SEC8" href="#TOC1">AUTHOR</a><br> |
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<P> |
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Philip Hazel |
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<br> |
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University Computing Service, |
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<br> |
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Cambridge CB2 3QH, England. |
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</P> |
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<P> |
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Last updated: 16 January 2006 |
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<br> |
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Copyright © 1997-2006 University of Cambridge. |
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<p> |
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Return to the <a href="index.html">PCRE index page</a>. |
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</p> |
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