Originální popis anglicky:
regcomp, regexec, regerror, regfree - POSIX regex functions
Návod, kniha: Linux Programmer's Manual
#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);
regcomp is used to compile a regular expression into a form that is
suitable for subsequent
regexec searches.
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
- Support for substring addressing of matches is not
required. The nmatch and pmatch parameters 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 non-matching 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.
regexec is used to match a null-terminated string against the precompiled
pattern buffer,
preg.
nmatch and
pmatch are used to
provide information regarding the location of any matches.
eflags may
be the bitwise-
or of one or both of
REG_NOTBOL and
REG_NOTEOL which cause changes in matching behaviour described below.
- 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)
Unless
REG_NOSUB was set for the compilation of the pattern buffer, it is
possible to obtain substring match addressing information.
pmatch must
be dimensioned to have at least
nmatch elements. These are filled in by
regexec with substring match addresses. Any unused structure elements
will contain the value -1.
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.
regerror is used to turn the error codes that can be returned by both
regcomp and
regexec into error message strings.
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 non-zero,
errbuf is
filled in with the first
errbuf_size - 1 characters of the error
message and a terminating null.
Supplying
regfree with a precompiled pattern buffer,
preg will
free the memory allocated to the pattern buffer by the compiling process,
regcomp.
regcomp returns zero for a successful compilation or an error code for
failure.
regexec returns zero for a successful match or
REG_NOMATCH for
failure.
The following errors can be returned by
regcomp:
- 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
`*' 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
- Non specific 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, eg. 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.
POSIX.2
regex(7), GNU regex manual
