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
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 .
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
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)
"BYTE OFFSETS" 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 .
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.
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_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.
