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<html>
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<head>
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<title>pcreposix specification</title>
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</head>
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<body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
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This HTML document has been generated automatically from the original man page.
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If there is any nonsense in it, please consult the man page, in case the
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conversion went wrong.<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">STORAGE</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 the native API, which contains additional
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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 which uses them. Because the POSIX functions
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call the native ones, it is also necessary to add \fR-lpcre\fR.
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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 options REG_EXTENDED and REG_NOSUB are defined
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with the value zero. They have no effect, but since programs that are written
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to the POSIX interface often use them, this makes it easier to slot in PCRE as
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a replacement 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.
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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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<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 regex_t structure which is used as a base for storing information about
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the compiled 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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</P>
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<P>
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<pre>
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REG_ICASE
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</PRE>
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</P>
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<P>
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The PCRE_CASELESS option is set when the expression is passed for compilation
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to the native function.
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</P>
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<P>
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<pre>
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REG_NEWLINE
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</PRE>
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</P>
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<P>
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The PCRE_MULTILINE option is set when the expression is passed for compilation
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to the native function. Note that this does <i>not</i> mimic the defined POSIX
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behaviour for REG_NEWLINE (see the following section).
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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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</P>
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<P>
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<pre>
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Default Change with
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</PRE>
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</P>
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<P>
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<pre>
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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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</P>
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<P>
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This is the equivalent table for POSIX:
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</P>
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<P>
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<pre>
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Default Change with
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</PRE>
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</P>
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<P>
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<pre>
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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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</P>
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<P>
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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_DOLLARENDONLY 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_DOLLARENDONLY, 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 pre-compiled pattern
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<i>preg</i> against a given <i>string</i>, which is terminated by a zero byte,
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subject to the options in <i>eflags</i>. These can be:
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</P>
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<P>
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<pre>
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REG_NOTBOL
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</PRE>
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</P>
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<P>
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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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</P>
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<P>
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<pre>
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REG_NOTEOL
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</PRE>
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</P>
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<P>
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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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The portion of the string that was matched, and also any captured substrings,
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are returned via the <i>pmatch</i> argument, which points to an array of
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<i>nmatch</i> structures of type <i>regmatch_t</i>, containing the members
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<i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first character of
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each substring and the offset to the first character after the end of each
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substring, respectively. The 0th element of the vector relates to the entire
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portion of <i>string</i> that was matched; subsequent elements relate to the
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capturing subpatterns of the regular expression. Unused entries in the array
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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">STORAGE</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 <ph10@cam.ac.uk>
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<br>
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University Computing Service,
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<br>
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Cambridge CB2 3QG, England.
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</P>
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<P>
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Last updated: 03 February 2003
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<br>
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Copyright © 1997-2003 University of Cambridge.
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