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regcomp, regexec, regerror, regfree - POSIX
regex functions
#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_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_ECOLLATE
- Invalid collating
element.
- REG_EPAREN
- Un-matched parenthesis group operators.
- REG_ESUBREG
- Invalid
back reference to a subexpression.
- REG_EEND
- Non specific error. This is
not defined by POSIX.2.
- REG_EESCAPE
- Trailing backslash.
- REG_BADPAT
- Invalid
use of pattern operators such as group or list.
- 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.
POSIX.2
regex(7)
, GNU regex manual
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