ossp-pkg/pcre/pcreposix.3
.TH PCRE 3
.SH NAME
pcreposix - POSIX API for Perl-compatible regular expressions.
.SH SYNOPSIS
.B #include <pcreposix.h>
.PP
.SM
.br
.B int regcomp(regex_t *\fIpreg\fR, const char *\fIpattern\fR,
.ti +5n
.B int \fIcflags\fR);
.PP
.br
.B int regexec(regex_t *\fIpreg\fR, const char *\fIstring\fR,
.ti +5n
.B size_t \fInmatch\fR, regmatch_t \fIpmatch\fR[], int \fIeflags\fR);
.PP
.br
.B size_t regerror(int \fIerrcode\fR, const regex_t *\fIpreg\fR,
.ti +5n
.B char *\fIerrbuf\fR, size_t \fIerrbuf_size\fR);
.PP
.br
.B void regfree(regex_t *\fIpreg\fR);
.SH DESCRIPTION
This set of functions provides a POSIX-style API to the PCRE regular expression
package. See the \fBpcre\fR documentation for a description of the native API,
which contains additional functionality.
The functions described here are just wrapper functions that ultimately call
the native API. Their prototypes are defined in the \fBpcreposix.h\fR header
file, and on Unix systems the library itself is called \fBpcreposix.a\fR, so
can be accessed by adding \fB-lpcreposix\fR to the command for linking an
application which uses them. Because the POSIX functions call the native ones,
it is also necessary to add \fR-lpcre\fR.
I have implemented only those option bits that can be reasonably mapped to PCRE
native options. In addition, the options REG_EXTENDED and REG_NOSUB are defined
with the value zero. They have no effect, but since programs that are written
to the POSIX interface often use them, this makes it easier to slot in PCRE as
a replacement library. Other POSIX options are not even defined.
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.
The header for these functions is supplied as \fBpcreposix.h\fR to avoid any
potential clash with other POSIX libraries. It can, of course, be renamed or
aliased as \fBregex.h\fR, which is the "correct" name. It provides two
structure types, \fIregex_t\fR for compiled internal forms, and
\fIregmatch_t\fR for returning captured substrings. It also defines some
constants whose names start with "REG_"; these are used for setting options and
identifying error codes.
.SH COMPILING A PATTERN
The function \fBregcomp()\fR 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 \fIpattern\fR. The \fIpreg\fR argument is a pointer
to a regex_t structure which is used as a base for storing information about
the compiled expression.
The argument \fIcflags\fR is either zero, or contains one or more of the bits
defined by the following macros:
REG_ICASE
The PCRE_CASELESS option is set when the expression is passed for compilation
to the native function.
REG_NEWLINE
The PCRE_MULTILINE option is set when the expression is passed for compilation
to the native function.
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
\fIsome\fR of the effects specified for REG_NEWLINE. It does not affect the way
newlines are matched by . (they aren't) or a negative class such as [^a] (they
are).
The yield of \fBregcomp()\fR is zero on success, and non-zero otherwise. The
\fIpreg\fR structure is filled in on success, and one member of the structure
is publicized: \fIre_nsub\fR contains the number of capturing subpatterns in
the regular expression. Various error codes are defined in the header file.
.SH MATCHING A PATTERN
The function \fBregexec()\fR is called to match a pre-compiled pattern
\fIpreg\fR against a given \fIstring\fR, which is terminated by a zero byte,
subject to the options in \fIeflags\fR. These can be:
REG_NOTBOL
The PCRE_NOTBOL option is set when calling the underlying PCRE matching
function.
REG_NOTEOL
The PCRE_NOTEOL option is set when calling the underlying PCRE matching
function.
The portion of the string that was matched, and also any captured substrings,
are returned via the \fIpmatch\fR argument, which points to an array of
\fInmatch\fR structures of type \fIregmatch_t\fR, containing the members
\fIrm_so\fR and \fIrm_eo\fR. 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 \fIstring\fR 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.
.SH ERROR MESSAGES
The \fBregerror()\fR function maps a non-zero errorcode from either
\fBregcomp\fR or \fBregexec\fR to a printable message. If \fIpreg\fR is not
NULL, the error should have arisen from the use of that structure. A message
terminated by a binary zero is placed in \fIerrbuf\fR. The length of the
message, including the zero, is limited to \fIerrbuf_size\fR. The yield of the
function is the size of buffer needed to hold the whole message.
.SH STORAGE
Compiling a regular expression causes memory to be allocated and associated
with the \fIpreg\fR structure. The function \fBregfree()\fR frees all such
memory, after which \fIpreg\fR may no longer be used as a compiled expression.
.SH AUTHOR
Philip Hazel <ph10@cam.ac.uk>
.br
University Computing Service,
.br
New Museums Site,
.br
Cambridge CB2 3QG, England.
.br
Phone: +44 1223 334714
Copyright (c) 1997-2000 University of Cambridge.
