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3 <title>pcreposix specification</title>
5 <body bgcolor="#FFFFFF" text="#00005A" link="#0066FF" alink="#3399FF" vlink="#2222BB">
6 <h1>pcreposix man page</h1>
8 Return to the <a href="index.html">PCRE index page</a>.
11 This page is part of the PCRE HTML documentation. It was generated automatically
12 from the original man page. If there is any nonsense in it, please consult the
13 man page, in case the conversion went wrong.
16 <li><a name="TOC1" href="#SEC1">SYNOPSIS</a>
17 <li><a name="TOC2" href="#SEC2">DESCRIPTION</a>
18 <li><a name="TOC3" href="#SEC3">COMPILING A PATTERN</a>
19 <li><a name="TOC4" href="#SEC4">MATCHING NEWLINE CHARACTERS</a>
20 <li><a name="TOC5" href="#SEC5">MATCHING A PATTERN</a>
21 <li><a name="TOC6" href="#SEC6">ERROR MESSAGES</a>
22 <li><a name="TOC7" href="#SEC7">MEMORY USAGE</a>
23 <li><a name="TOC8" href="#SEC8">AUTHOR</a>
24 <li><a name="TOC9" href="#SEC9">REVISION</a>
26 <br><a name="SEC1" href="#TOC1">SYNOPSIS</a><br>
28 <b>#include <pcreposix.h></b>
31 <b>int regcomp(regex_t *<i>preg</i>, const char *<i>pattern</i>,</b>
32 <b> int <i>cflags</i>);</b>
35 <b>int regexec(regex_t *<i>preg</i>, const char *<i>string</i>,</b>
36 <b> size_t <i>nmatch</i>, regmatch_t <i>pmatch</i>, int <i>eflags</i>);</b>
37 <b> size_t regerror(int <i>errcode</i>, const regex_t *<i>preg</i>,</b>
38 <b> char *<i>errbuf</i>, size_t <i>errbuf_size</i>);</b>
41 <b>void regfree(regex_t *<i>preg</i>);</b>
43 <br><a name="SEC2" href="#TOC1">DESCRIPTION</a><br>
45 This set of functions provides a POSIX-style API for the PCRE regular
46 expression 8-bit library. See the
47 <a href="pcreapi.html"><b>pcreapi</b></a>
48 documentation for a description of PCRE's native API, which contains much
49 additional functionality. There is no POSIX-style wrapper for PCRE's 16-bit
50 and 32-bit library.
53 The functions described here are just wrapper functions that ultimately call
54 the PCRE native API. Their prototypes are defined in the <b>pcreposix.h</b>
55 header file, and on Unix systems the library itself is called
56 <b>pcreposix.a</b>, so can be accessed by adding <b>-lpcreposix</b> to the
57 command for linking an application that uses them. Because the POSIX functions
58 call the native ones, it is also necessary to add <b>-lpcre</b>.
61 I have implemented only those POSIX option bits that can be reasonably mapped
62 to PCRE native options. In addition, the option REG_EXTENDED is defined with
63 the value zero. This has no effect, but since programs that are written to the
64 POSIX interface often use it, this makes it easier to slot in PCRE as a
65 replacement library. Other POSIX options are not even defined.
68 There are also some other options that are not defined by POSIX. These have
69 been added at the request of users who want to make use of certain
70 PCRE-specific features via the POSIX calling interface.
73 When PCRE is called via these functions, it is only the API that is POSIX-like
74 in style. The syntax and semantics of the regular expressions themselves are
75 still those of Perl, subject to the setting of various PCRE options, as
76 described below. "POSIX-like in style" means that the API approximates to the
77 POSIX definition; it is not fully POSIX-compatible, and in multi-byte encoding
78 domains it is probably even less compatible.
81 The header for these functions is supplied as <b>pcreposix.h</b> to avoid any
82 potential clash with other POSIX libraries. It can, of course, be renamed or
83 aliased as <b>regex.h</b>, which is the "correct" name. It provides two
84 structure types, <i>regex_t</i> for compiled internal forms, and
85 <i>regmatch_t</i> for returning captured substrings. It also defines some
86 constants whose names start with "REG_"; these are used for setting options and
87 identifying error codes.
89 <br><a name="SEC3" href="#TOC1">COMPILING A PATTERN</a><br>
91 The function <b>regcomp()</b> is called to compile a pattern into an
92 internal form. The pattern is a C string terminated by a binary zero, and
93 is passed in the argument <i>pattern</i>. The <i>preg</i> argument is a pointer
94 to a <b>regex_t</b> structure that is used as a base for storing information
95 about the compiled regular expression.
98 The argument <i>cflags</i> is either zero, or contains one or more of the bits
99 defined by the following macros:
103 The PCRE_DOTALL option is set when the regular expression is passed for
104 compilation to the native function. Note that REG_DOTALL is not part of the
105 POSIX standard.
109 The PCRE_CASELESS option is set when the regular expression is passed for
110 compilation to the native function.
114 The PCRE_MULTILINE option is set when the regular expression is passed for
115 compilation to the native function. Note that this does <i>not</i> mimic the
116 defined POSIX behaviour for REG_NEWLINE (see the following section).
120 The PCRE_NO_AUTO_CAPTURE option is set when the regular expression is passed
121 for compilation to the native function. In addition, when a pattern that is
122 compiled with this flag is passed to <b>regexec()</b> for matching, the
123 <i>nmatch</i> and <i>pmatch</i> arguments are ignored, and no captured strings
124 are returned.
128 The PCRE_UCP option is set when the regular expression is passed for
129 compilation to the native function. This causes PCRE to use Unicode properties
130 when matchine \d, \w, etc., instead of just recognizing ASCII values. Note
131 that REG_UTF8 is not part of the POSIX standard.
135 The PCRE_UNGREEDY option is set when the regular expression is passed for
136 compilation to the native function. Note that REG_UNGREEDY is not part of the
137 POSIX standard.
141 The PCRE_UTF8 option is set when the regular expression is passed for
142 compilation to the native function. This causes the pattern itself and all data
143 strings used for matching it to be treated as UTF-8 strings. Note that REG_UTF8
144 is not part of the POSIX standard.
147 In the absence of these flags, no options are passed to the native function.
148 This means the the regex is compiled with PCRE default semantics. In
149 particular, the way it handles newline characters in the subject string is the
150 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
151 <i>some</i> of the effects specified for REG_NEWLINE. It does not affect the way
152 newlines are matched by . (they are not) or by a negative class such as [^a]
153 (they are).
156 The yield of <b>regcomp()</b> is zero on success, and non-zero otherwise. The
157 <i>preg</i> structure is filled in on success, and one member of the structure
158 is public: <i>re_nsub</i> contains the number of capturing subpatterns in
159 the regular expression. Various error codes are defined in the header file.
162 NOTE: If the yield of <b>regcomp()</b> is non-zero, you must not attempt to
163 use the contents of the <i>preg</i> structure. If, for example, you pass it to
164 <b>regexec()</b>, the result is undefined and your program is likely to crash.
166 <br><a name="SEC4" href="#TOC1">MATCHING NEWLINE CHARACTERS</a><br>
168 This area is not simple, because POSIX and Perl take different views of things.
169 It is not possible to get PCRE to obey POSIX semantics, but then PCRE was never
170 intended to be a POSIX engine. The following table lists the different
171 possibilities for matching newline characters in PCRE:
173 Default Change with
175 . matches newline no PCRE_DOTALL
176 newline matches [^a] yes not changeable
177 $ matches \n at end yes PCRE_DOLLARENDONLY
178 $ matches \n in middle no PCRE_MULTILINE
179 ^ matches \n in middle no PCRE_MULTILINE
181 This is the equivalent table for POSIX:
183 Default Change with
185 . matches newline yes REG_NEWLINE
186 newline matches [^a] yes REG_NEWLINE
187 $ matches \n at end no REG_NEWLINE
188 $ matches \n in middle no REG_NEWLINE
189 ^ matches \n in middle no REG_NEWLINE
191 PCRE's behaviour is the same as Perl's, except that there is no equivalent for
192 PCRE_DOLLAR_ENDONLY in Perl. In both PCRE and Perl, there is no way to stop
193 newline from matching [^a].
196 The default POSIX newline handling can be obtained by setting PCRE_DOTALL and
197 PCRE_DOLLAR_ENDONLY, but there is no way to make PCRE behave exactly as for the
198 REG_NEWLINE action.
200 <br><a name="SEC5" href="#TOC1">MATCHING A PATTERN</a><br>
202 The function <b>regexec()</b> is called to match a compiled pattern <i>preg</i>
203 against a given <i>string</i>, which is by default terminated by a zero byte
204 (but see REG_STARTEND below), subject to the options in <i>eflags</i>. These can
209 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
214 The PCRE_NOTEMPTY option is set when calling the underlying PCRE matching
215 function. Note that REG_NOTEMPTY is not part of the POSIX standard. However,
216 setting this option can give more POSIX-like behaviour in some situations.
220 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
225 The string is considered to start at <i>string</i> + <i>pmatch.rm_so</i> and
226 to have a terminating NUL located at <i>string</i> + <i>pmatch.rm_eo</i>
227 (there need not actually be a NUL at that location), regardless of the value of
228 <i>nmatch</i>. This is a BSD extension, compatible with but not specified by
229 IEEE Standard 1003.2 (POSIX.2), and should be used with caution in software
230 intended to be portable to other systems. Note that a non-zero <i>rm_so</i> does
231 not imply REG_NOTBOL; REG_STARTEND affects only the location of the string, not
232 how it is matched.
235 If the pattern was compiled with the REG_NOSUB flag, no data about any matched
236 strings is returned. The <i>nmatch</i> and <i>pmatch</i> arguments of
237 <b>regexec()</b> are ignored.
240 If the value of <i>nmatch</i> is zero, or if the value <i>pmatch</i> is NULL,
241 no data about any matched strings is returned.
244 Otherwise,the portion of the string that was matched, and also any captured
245 substrings, are returned via the <i>pmatch</i> argument, which points to an
246 array of <i>nmatch</i> structures of type <i>regmatch_t</i>, containing the
247 members <i>rm_so</i> and <i>rm_eo</i>. These contain the offset to the first
248 character of each substring and the offset to the first character after the end
249 of each substring, respectively. The 0th element of the vector relates to the
250 entire portion of <i>string</i> that was matched; subsequent elements relate to
251 the capturing subpatterns of the regular expression. Unused entries in the
252 array have both structure members set to -1.
255 A successful match yields a zero return; various error codes are defined in the
256 header file, of which REG_NOMATCH is the "expected" failure code.
258 <br><a name="SEC6" href="#TOC1">ERROR MESSAGES</a><br>
260 The <b>regerror()</b> function maps a non-zero errorcode from either
261 <b>regcomp()</b> or <b>regexec()</b> to a printable message. If <i>preg</i> is not
262 NULL, the error should have arisen from the use of that structure. A message
263 terminated by a binary zero is placed in <i>errbuf</i>. The length of the
264 message, including the zero, is limited to <i>errbuf_size</i>. The yield of the
265 function is the size of buffer needed to hold the whole message.
267 <br><a name="SEC7" href="#TOC1">MEMORY USAGE</a><br>
269 Compiling a regular expression causes memory to be allocated and associated
270 with the <i>preg</i> structure. The function <b>regfree()</b> frees all such
271 memory, after which <i>preg</i> may no longer be used as a compiled expression.
273 <br><a name="SEC8" href="#TOC1">AUTHOR</a><br>
275 Philip Hazel
277 University Computing Service
279 Cambridge CB2 3QH, England.
282 <br><a name="SEC9" href="#TOC1">REVISION</a><br>
284 Last updated: 09 January 2012
286 Copyright © 1997-2012 University of Cambridge.
289 Return to the <a href="index.html">PCRE index page</a>.