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-NAME
- pcreposix - POSIX API for Perl-compatible regular expres-
- sions.
-
-
-
-SYNOPSIS
- #include <pcreposix.h>
-
- int regcomp(regex_t *preg, const char *pattern,
- int cflags);
-
- int regexec(regex_t *preg, const char *string,
- size_t nmatch, regmatch_t pmatch[], int eflags);
-
- size_t regerror(int errcode, const regex_t *preg,
- char *errbuf, size_t errbuf_size);
-
- void regfree(regex_t *preg);
-
-
-
-DESCRIPTION
- This set of functions provides a POSIX-style API to the PCRE
- regular expression package. See the pcre 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 pcreposix.h header file, and on Unix systems the
- library itself is called pcreposix.a, so can be accessed by
- adding -lpcreposix to the command for linking an application
- which uses them. Because the POSIX functions call the native
- ones, it is also necessary to add -lpcre.
-
- As I am pretty ignorant about POSIX, these functions must be
- considered as experimental. I have implemented only those
- option bits that can be reasonably mapped to PCRE native
- options. Other POSIX options are not even defined. It may be
- that it is useful to define, but ignore, other options.
- Feedback from more knowledgeable folk may cause this kind of
- detail to change.
-
- 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, sub-
- ject to the setting of various PCRE options, as described
- below.
-
- The header for these functions is supplied as pcreposix.h to
- avoid any potential clash with other POSIX libraries. It
- can, of course, be renamed or aliased as regex.h, which is
- the "correct" name. It provides two structure types, regex_t
- for compiled internal forms, and regmatch_t for returning
- captured substrings. It also defines some constants whose
- names start with "REG_"; these are used for setting options
- and identifying error codes.
-
-
-
-COMPILING A PATTERN
- The function regcomp() 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 pattern. The preg
- argument is a pointer to a regex_t structure which is used
- as a base for storing information about the compiled expres-
- sion.
-
- The argument cflags 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.
-
- The yield of regcomp() is zero on success, and non-zero oth-
- erwise. The preg structure is filled in on success, and one
- member of the structure is publicized: re_nsub contains the
- number of capturing subpatterns in the regular expression.
- Various error codes are defined in the header file.
-
-
-
-MATCHING A PATTERN
- The function regexec() is called to match a pre-compiled
- pattern preg against a given string, which is terminated by
- a zero byte, subject to the options in eflags. 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 pmatch argument,
- which points to an array of nmatch structures of type
- regmatch_t, containing the members rm_so and rm_eo. 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 string 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.
-
-
-
-ERROR MESSAGES
- The regerror() function maps a non-zero errorcode from
- either regcomp or regexec to a printable message. If preg is
- not NULL, the error should have arisen from the use of that
- structure. A message terminated by a binary zero is placed
- in errbuf. The length of the message, including the zero, is
- limited to errbuf_size. The yield of the function is the
- size of buffer needed to hold the whole message.
-
-
-
-STORAGE
- Compiling a regular expression causes memory to be allocated
- and associated with the preg structure. The function reg-
- free() frees all such memory, after which preg may no longer
- be used as a compiled expression.
-
-
-
-AUTHOR
- Philip Hazel <ph10@cam.ac.uk>
- University Computing Service,
- New Museums Site,
- Cambridge CB2 3QG, England.
- Phone: +44 1223 334714
-
- Copyright (c) 1997-1999 University of Cambridge.