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Synopsis

#include <sys/types.h>#include <regex.h>int regcomp(regex_t *preg, const char
*regex, int cflags);int regexec(const 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

POSIX regex compiling

regcomp() is supplied with preg, a pointer to a pattern buffer storage area; regex, a pointer to the null-terminated string and cflags, flags used to determine the type of compilation.

All regular expression searching must be done via a compiled pattern buffer, thus regexec() must always be supplied with the address of a regcomp() initialized pattern buffer.

cflags may be the bitwise-or of one or more of the following:

REG_EXTENDED

Use POSIX Extended Regular Expression syntax when interpreting regex. If not set, POSIX Basic Regular Expression syntax is used.

REG_ICASE

Do not differentiate case. Subsequent regexec() searches using this pattern buffer will be case insensitive.

REG_NOSUB

Do not report position of matches. The nmatch and pmatch arguments to regexec() are ignored if the pattern buffer supplied was compiled with this flag set.

REG_NEWLINE

Match-any-character operators don’t match a newline.

A nonmatching list ([^...]) not containing a newline does not match a newline.

Match-beginning-of-line operator (^) matches the empty string immediately after a newline, regardless of whether eflags, the execution flags of regexec(), contains REG_NOTBOL.

Match-end-of-line operator ($) matches the empty string immediately before a newline, regardless of whether eflags contains REG_NOTEOL.

POSIX regex matching

REG_NOTBOL

The match-beginning-of-line operator always fails to match (but see the compilation flag REG_NEWLINE above). This flag may be used when different portions of a string are passed to regexec() and the beginning of the string should not be interpreted as the beginning of the line.

REG_NOTEOL

The match-end-of-line operator always fails to match (but see the compilation flag REG_NEWLINE above).

Byte offsets

The regmatch_t structure which is the type of pmatch is defined in <regex.h>.

typedef struct {
    regoff_t rm_so;
    regoff_t rm_eo;
} regmatch_t;

Each rm_so element that is not -1 indicates the start offset of the next largest substring match within the string. The relative rm_eo element indicates the end offset of the match, which is the offset of the first character after the matching text.

POSIX error reporting

regerror() is passed the error code, errcode, the pattern buffer, preg, a pointer to a character string buffer, errbuf, and the size of the string buffer, errbuf_size. It returns the size of the errbuf required to contain the null-terminated error message string. If both errbuf and errbuf_size are nonzero, errbuf is filled in with the first errbuf_size - 1 characters of the error message and a terminating null byte (aq\0aq).

POSIX pattern buffer freeing

Return Value

regexec() returns zero for a successful match or REG_NOMATCH for failure.

Errors

REG_BADBR

Invalid use of back reference operator.

REG_BADPAT

Invalid use of pattern operators such as group or list.

REG_BADRPT

Invalid use of repetition operators such as using aq*aq as the first character.

REG_EBRACE

Un-matched brace interval operators.

REG_EBRACK

Un-matched bracket list operators.

REG_ECOLLATE

Invalid collating element.

REG_ECTYPE

Unknown character class name.

REG_EEND

Nonspecific error. This is not defined by POSIX.2.

REG_EESCAPE

Trailing backslash.

REG_EPAREN

Un-matched parenthesis group operators.

REG_ERANGE

Invalid use of the range operator; for example, the ending point of the range occurs prior to the starting point.

REG_ESIZE

Compiled regular expression requires a pattern buffer larger than 64Kb. This is not defined by POSIX.2.

REG_ESPACE

The regex routines ran out of memory.

REG_ESUBREG

Invalid back reference to a subexpression.

Conforming to

See Also

Colophon

Table of Contents

• Name
• Synopsis
• Description
• POSIX regex compiling
• POSIX regex matching
• Byte offsets
• POSIX error reporting
• POSIX pattern buffer freeing
• Return Value
• Errors
• Conforming to
• See Also
• Colophon