/[pcre]/code/trunk/doc/pcreposix.3
ViewVC logotype

Contents of /code/trunk/doc/pcreposix.3

Parent Directory Parent Directory | Revision Log Revision Log


Revision 49 - (show annotations) (download)
Sat Feb 24 21:39:33 2007 UTC (7 years, 7 months ago) by nigel
File size: 5888 byte(s)
Load pcre-3.3 into code/trunk.

1 .TH PCRE 3
2 .SH NAME
3 pcreposix - POSIX API for Perl-compatible regular expressions.
4 .SH SYNOPSIS
5 .B #include <pcreposix.h>
6 .PP
7 .SM
8 .br
9 .B int regcomp(regex_t *\fIpreg\fR, const char *\fIpattern\fR,
10 .ti +5n
11 .B int \fIcflags\fR);
12 .PP
13 .br
14 .B int regexec(regex_t *\fIpreg\fR, const char *\fIstring\fR,
15 .ti +5n
16 .B size_t \fInmatch\fR, regmatch_t \fIpmatch\fR[], int \fIeflags\fR);
17 .PP
18 .br
19 .B size_t regerror(int \fIerrcode\fR, const regex_t *\fIpreg\fR,
20 .ti +5n
21 .B char *\fIerrbuf\fR, size_t \fIerrbuf_size\fR);
22 .PP
23 .br
24 .B void regfree(regex_t *\fIpreg\fR);
25
26
27 .SH DESCRIPTION
28 This set of functions provides a POSIX-style API to the PCRE regular expression
29 package. See the \fBpcre\fR documentation for a description of the native API,
30 which contains additional functionality.
31
32 The functions described here are just wrapper functions that ultimately call
33 the native API. Their prototypes are defined in the \fBpcreposix.h\fR header
34 file, and on Unix systems the library itself is called \fBpcreposix.a\fR, so
35 can be accessed by adding \fB-lpcreposix\fR to the command for linking an
36 application which uses them. Because the POSIX functions call the native ones,
37 it is also necessary to add \fR-lpcre\fR.
38
39 I have implemented only those option bits that can be reasonably mapped to PCRE
40 native options. In addition, the options REG_EXTENDED and REG_NOSUB are defined
41 with the value zero. They have no effect, but since programs that are written
42 to the POSIX interface often use them, this makes it easier to slot in PCRE as
43 a replacement library. Other POSIX options are not even defined.
44
45 When PCRE is called via these functions, it is only the API that is POSIX-like
46 in style. The syntax and semantics of the regular expressions themselves are
47 still those of Perl, subject to the setting of various PCRE options, as
48 described below.
49
50 The header for these functions is supplied as \fBpcreposix.h\fR to avoid any
51 potential clash with other POSIX libraries. It can, of course, be renamed or
52 aliased as \fBregex.h\fR, which is the "correct" name. It provides two
53 structure types, \fIregex_t\fR for compiled internal forms, and
54 \fIregmatch_t\fR for returning captured substrings. It also defines some
55 constants whose names start with "REG_"; these are used for setting options and
56 identifying error codes.
57
58
59 .SH COMPILING A PATTERN
60
61 The function \fBregcomp()\fR is called to compile a pattern into an
62 internal form. The pattern is a C string terminated by a binary zero, and
63 is passed in the argument \fIpattern\fR. The \fIpreg\fR argument is a pointer
64 to a regex_t structure which is used as a base for storing information about
65 the compiled expression.
66
67 The argument \fIcflags\fR is either zero, or contains one or more of the bits
68 defined by the following macros:
69
70 REG_ICASE
71
72 The PCRE_CASELESS option is set when the expression is passed for compilation
73 to the native function.
74
75 REG_NEWLINE
76
77 The PCRE_MULTILINE option is set when the expression is passed for compilation
78 to the native function.
79
80 In the absence of these flags, no options are passed to the native function.
81 This means the the regex is compiled with PCRE default semantics. In
82 particular, the way it handles newline characters in the subject string is the
83 Perl way, not the POSIX way. Note that setting PCRE_MULTILINE has only
84 \fIsome\fR of the effects specified for REG_NEWLINE. It does not affect the way
85 newlines are matched by . (they aren't) or a negative class such as [^a] (they
86 are).
87
88 The yield of \fBregcomp()\fR is zero on success, and non-zero otherwise. The
89 \fIpreg\fR structure is filled in on success, and one member of the structure
90 is publicized: \fIre_nsub\fR contains the number of capturing subpatterns in
91 the regular expression. Various error codes are defined in the header file.
92
93
94 .SH MATCHING A PATTERN
95 The function \fBregexec()\fR is called to match a pre-compiled pattern
96 \fIpreg\fR against a given \fIstring\fR, which is terminated by a zero byte,
97 subject to the options in \fIeflags\fR. These can be:
98
99 REG_NOTBOL
100
101 The PCRE_NOTBOL option is set when calling the underlying PCRE matching
102 function.
103
104 REG_NOTEOL
105
106 The PCRE_NOTEOL option is set when calling the underlying PCRE matching
107 function.
108
109 The portion of the string that was matched, and also any captured substrings,
110 are returned via the \fIpmatch\fR argument, which points to an array of
111 \fInmatch\fR structures of type \fIregmatch_t\fR, containing the members
112 \fIrm_so\fR and \fIrm_eo\fR. These contain the offset to the first character of
113 each substring and the offset to the first character after the end of each
114 substring, respectively. The 0th element of the vector relates to the entire
115 portion of \fIstring\fR that was matched; subsequent elements relate to the
116 capturing subpatterns of the regular expression. Unused entries in the array
117 have both structure members set to -1.
118
119 A successful match yields a zero return; various error codes are defined in the
120 header file, of which REG_NOMATCH is the "expected" failure code.
121
122
123 .SH ERROR MESSAGES
124 The \fBregerror()\fR function maps a non-zero errorcode from either
125 \fBregcomp\fR or \fBregexec\fR to a printable message. If \fIpreg\fR is not
126 NULL, the error should have arisen from the use of that structure. A message
127 terminated by a binary zero is placed in \fIerrbuf\fR. The length of the
128 message, including the zero, is limited to \fIerrbuf_size\fR. The yield of the
129 function is the size of buffer needed to hold the whole message.
130
131
132 .SH STORAGE
133 Compiling a regular expression causes memory to be allocated and associated
134 with the \fIpreg\fR structure. The function \fBregfree()\fR frees all such
135 memory, after which \fIpreg\fR may no longer be used as a compiled expression.
136
137
138 .SH AUTHOR
139 Philip Hazel <ph10@cam.ac.uk>
140 .br
141 University Computing Service,
142 .br
143 New Museums Site,
144 .br
145 Cambridge CB2 3QG, England.
146 .br
147 Phone: +44 1223 334714
148
149 Copyright (c) 1997-2000 University of Cambridge.

webmaster@exim.org
ViewVC Help
Powered by ViewVC 1.1.12