regcomp(3)
NAME
regcomp, regexec, regerror, regfree - POSIX regex func-
tions
SYNOPSIS
#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);
POSIX REGEX COMPILING
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-termi-
nated string and cflags, flags used to determine the type
of compilation.
All regular expression searching must be done via a com-
piled pattern buffer, thus regexec must always be supplied
with the address of a regcomp initialised pattern buffer.
cflags may be the bitwise-or of one or more of the follow-
ing:
REG_EXTENDED
Use POSIX Extended Regular Expression syntax when
interpreting regex. If not set, POSIX Basic Regu-
lar 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 new-
line.
A non-matching list ([^...]) not containing a new-
line matches a newline.
Match-beginning-of-line operator (^) matches the
empty string immediately after a newline, regard-
less 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
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 match-
ing 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 por-
tions 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
Unless REG_NOSUB was set for the compilation of the pat-
tern 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 struc-
ture 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 off-
set of the next largest substring match within the string.
The relative rm_eo element indicates the end offset of the
match.
POSIX ERROR REPORTING
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.
POSIX PATTERN BUFFER FREEING
Supplying regfree with a precompiled pattern buffer, preg
will free the memory allocated to the pattern buffer by
the compiling process, regcomp.
RETURN VALUE
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.
ERRORS
The following errors can be returned by regcomp:
REG_BADRPT
Invalid use of repetition operators such as using
`*' as the first character.
REG_BADBR
Invalid use of back reference operator.
REG_EBRACE
Un-matched brace interval operators.
REG_EBRACK
Un-matched bracket list operators.
REG_ERANGE
Invalid use of the range operator, eg. the ending
point of the range occurs prior to the starting
point.
REG_ECTYPE
Unknown character class name.
REG_EPAREN
Un-matched parenthesis group operators.
REG_ESUBREG
Invalid back reference to a subexpression.
REG_EEND
Non specific error.
REG_ESCAPE
Invalid escape sequence.
REG_BADPAT
Invalid use of pattern operators such as group or
list.
REG_ESIZE
Compiled regular expression requires a pattern
buffer larger than 64Kb.
REG_ESPACE
The regex routines ran out of memory.
CONFORMING TO
POSIX
SEE ALSO
regex(7) GNU regex manual