regcomp(3C) Standard C Library Functions regcomp(3C)NAME
regcomp, regexec, regerror, regfree - regular expression matching
SYNOPSIS
#include <sys/types.h>
#include <regex.h>
int regcomp(regex_t *restrict preg, const char *restrict pattern, int
cflags);
int regexec(const regex_t *restrict preg, const char *restrict string,
size_t nmatch, regmatch_t pmatch[restrict], int eflags);
size_t regerror(int errcode, const regex_t *restrict preg, char
*restrict errbuf, size_t errbuf_size);
void regfree(regex_t *preg);
DESCRIPTION
These functions interpret basic and extended regular expressions
(described on the regex(5) manual page).
The structure type regex_t contains at least the following member:
size_t re_nsub Number of parenthesised subexpressions.
The structure type regmatch_t contains at least the following members:
regoff_t rm_so Byte offset from start of string to start of
substring.
regoff_t rm_eo Byte offset from start of string of the first
character after the end of substring.
regcomp()
The regcomp() function will compile the regular expression contained in
the string pointed to by the pattern argument and place the results in
the structure pointed to by preg. The cflags argument is the bitwise
inclusive OR of zero or more of the following flags, which are defined
in the header <regex.h>:
REG_EXTENDED Use Extended Regular Expressions.
REG_ICASE Ignore case in match.
REG_NOSUB Report only success/fail in regexec().
REG_NEWLINE Change the handling of NEWLINE characters, as described
in the text.
The default regular expression type for pattern is a Basic Regular
Expression. The application can specify Extended Regular Expressions
using the REG_EXTENDED cflags flag.
If the REG_NOSUB flag was not set in cflags, then regcomp() will set
re_nsub to the number of parenthesised subexpressions (delimited by
\(\) in basic regular expressions or () in extended regular expres‐
sions) found in pattern.
regexec()
The regexec() function compares the null-terminated string specified by
string with the compiled regular expression preg initialized by a pre‐
vious call to regcomp(). The eflags argument is the bitwise inclusive
OR of zero or more of the following flags, which are defined in the
header <regex.h>:
REG_NOTBOL The first character of the string pointed to by string
is not the beginning of the line. Therefore, the cir‐
cumflex character (^), when taken as a special charac‐
ter, will not match the beginning of string.
REG_NOTEOL The last character of the string pointed to by string
is not the end of the line. Therefore, the dollar sign
($), when taken as a special character, will not match
the end of string.
If nmatch is zero or REG_NOSUB was set in the cflags argument to reg‐
comp(), then regexec() will ignore the pmatch argument. Otherwise, the
pmatch argument must point to an array with at least nmatch elements,
and regexec() will fill in the elements of that array with offsets of
the substrings of string that correspond to the parenthesised subex‐
pressions of pattern: pmatch[i].rm_so will be the byte offset of the
beginning and pmatch[i].rm_eo will be one greater than the byte offset
of the end of substring i. (Subexpression i begins at the ith matched
open parenthesis, counting from 1.) Offsets in pmatch[0] identify the
substring that corresponds to the entire regular expression. Unused
elements of pmatch up to pmatch[nmatch−1] will be filled with −1. If
there are more than nmatch subexpressions in pattern (pattern itself
counts as a subexpression), then regexec() will still do the match, but
will record only the first nmatch substrings.
When matching a basic or extended regular expression, any given paren‐
thesised subexpression of pattern might participate in the match of
several different substrings of string, or it might not match any sub‐
string even though the pattern as a whole did match. The following
rules are used to determine which substrings to report in pmatch when
matching regular expressions:
1. If subexpression i in a regular expression is not contained
within another subexpression, and it participated in the match
several times, then the byte offsets in pmatch[i] will delimit
the last such match.
2. If subexpression i is not contained within another subexpres‐
sion, and it did not participate in an otherwise successful
match, the byte offsets in pmatch[i] will be −1. A subexpres‐
sion does not participate in the match when:
* or \{\} appears immediately after the subexpression in a
basic regular expression, or *, ?, or {} appears immediately
after the subexpression in an extended regular expression, and
the subexpression did not match (matched zero times)
or
| is used in an extended regular expression to select this
subexpression or another, and the other subexpression matched.
3. If subexpression i is contained within another subexpression
j, and i is not contained within any other subexpression that
is contained within j, and a match of subexpression j is
reported in pmatch[j], then the match or non-match of subex‐
pression i reported in pmatch[i] will be as described in 1.
and 2. above, but within the substring reported in pmatch[j]
rather than the whole string.
4. If subexpression i is contained in subexpression j, and the
byte offsets in pmatch[j] are −1, then the pointers in
pmatch[i] also will be −1.
5. If subexpression i matched a zero-length string, then both
byte offsets in pmatch[i] will be the byte offset of the char‐
acter or NULL terminator immediately following the zero-length
string.
If, when regexec() is called, the locale is different from when the
regular expression was compiled, the result is undefined.
If REG_NEWLINE is not set in cflags, then a NEWLINE character in pat‐
tern or string will be treated as an ordinary character. If REG_NEWLINE
is set, then newline will be treated as an ordinary character except as
follows:
1. A NEWLINE character in string will not be matched by a period
outside a bracket expression or by any form of a non-matching
list.
2. A circumflex (^) in pattern, when used to specify expression
anchoring will match the zero-length string immediately after
a newline in string, regardless of the setting of REG_NOTBOL.
3. A dollar-sign ($) in pattern, when used to specify expression
anchoring, will match the zero-length string immediately
before a newline in string, regardless of the setting of
REG_NOTEOL.
regfree()
The regfree() function frees any memory allocated by regcomp() associ‐
ated with preg.
The following constants are defined as error return values:
REG_NOMATCH The regexec() function failed to match.
REG_BADPAT Invalid regular expression.
REG_ECOLLATE Invalid collating element referenced.
REG_ECTYPE Invalid character class type referenced.
REG_EESCAPE Trailing \ in pattern.
REG_ESUBREG Number in \digit invalid or in error.
REG_EBRACK [] imbalance.
REG_ENOSYS The function is not supported.
REG_EPAREN \(\) or () imbalance.
REG_EBRACE \{ \} imbalance.
REG_BADBR Content of \{ \} invalid: not a number, number too
large, more than two numbers, first larger than second.
REG_ERANGE Invalid endpoint in range expression.
REG_ESPACE Out of memory.
REG_BADRPT ?, * or + not preceded by valid regular expression.
regerror()
The regerror() function provides a mapping from error codes returned by
regcomp() and regexec() to unspecified printable strings. It generates
a string corresponding to the value of the errcode argument, which must
be the last non-zero value returned by regcomp() or regexec() with the
given value of preg. If errcode is not such a value, an error message
indicating that the error code is invalid is returned.
If preg is a NULL pointer, but errcode is a value returned by a previ‐
ous call to regexec() or regcomp(), the regerror() still generates an
error string corresponding to the value of errcode.
If the errbuf_size argument is not zero, regerror() will place the gen‐
erated string into the buffer of size errbuf_size bytes pointed to by
errbuf. If the string (including the terminating NULL) cannot fit in
the buffer, regerror() will truncate the string and null-terminate the
result.
If errbuf_size is zero, regerror() ignores the errbuf argument, and
returns the size of the buffer needed to hold the generated string.
If the preg argument to regexec() or regfree() is not a compiled regu‐
lar expression returned by regcomp(), the result is undefined. A preg
is no longer treated as a compiled regular expression after it is given
to regfree().
See regex(5) for BRE (Basic Regular Expression) Anchoring.
RETURN VALUES
On successful completion, the regcomp() function returns 0. Otherwise,
it returns an integer value indicating an error as described in
<regex.h>, and the content of preg is undefined.
On successful completion, the regexec() function returns 0. Otherwise
it returns REG_NOMATCH to indicate no match, or REG_ENOSYS to indicate
that the function is not supported.
Upon successful completion, the regerror() function returns the number
of bytes needed to hold the entire generated string. Otherwise, it
returns 0 to indicate that the function is not implemented.
The regfree() function returns no value.
ERRORS
No errors are defined.
USAGE
An application could use:
regerror(code,preg,(char *)NULL,(size_t)0)
to find out how big a buffer is needed for the generated string, malloc
a buffer to hold the string, and then call regerror() again to get the
string (see malloc(3C)). Alternately, it could allocate a fixed, static
buffer that is big enough to hold most strings, and then use malloc()
to allocate a larger buffer if it finds that this is too small.
EXAMPLES
Example 1: Example to match string against the extended regular expres‐
sion in pattern.
#include <regex.h>
/*
* Match string against the extended regular expression in
* pattern, treating errors as no match.
*
* return 1 for match, 0 for no match
*/
int
match(const char *string, char *pattern)
{
int status;
regex_t re;
if (regcomp(&re, pattern, REG_EXTENDED|REG_NOSUB) != 0) {
return(0); /* report error */
}
status = regexec(&re, string, (size_t) 0, NULL, 0);
regfree(&re);
if (status != 0) {
return(0); /* report error */
}
return(1);
}
The following demonstrates how the REG_NOTBOL flag could be used with
regexec() to find all substrings in a line that match a pattern sup‐
plied by a user. (For simplicity of the example, very little error
checking is done.)
(void) regcomp (&re, pattern, 0);
/* this call to regexec() finds the first match on the line */
error = regexec (&re, &buffer[0], 1, &pm, 0);
while (error == 0) { /* while matches found */
/* substring found between pm.rm_so and pm.rm_eo */
/* This call to regexec() finds the next match */
error = regexec (&re, buffer + pm.rm_eo, 1, &pm, REG_NOTBOL);
}
ATTRIBUTES
See attributes(5) for descriptions of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
├─────────────────────────────┼─────────────────────────────┤
│CSI │Enabled │
├─────────────────────────────┼─────────────────────────────┤
│Interface Stability │Standard │
├─────────────────────────────┼─────────────────────────────┤
│MT-Level │MT-Safe with exceptions │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOfnmatch(3C), glob(3C), malloc(3C), setlocale(3C), attributes(5), stan‐
dards(5), regex(5)NOTES
The regcomp() function can be used safely in a multithreaded applica‐
tion as long as setlocale(3C) is not being called to change the locale.
SunOS 5.10 1 Nov 2003 regcomp(3C)
