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 expressions) found in  pattern.

   regexec()
       The  regexec()  function compares the null-terminated string specified by string with the compiled regular expression preg initialized by a
       previous 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 circumflex charac-
		       ter (^), when taken as a special character, 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 regcomp(), 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 subexpressions 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 parenthesised subexpression of pattern might participate in the match of
       several different substrings of string, or it might not match any substring 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 subexpression, and it did not participate in an otherwise successful match, the
		byte offsets in pmatch[i] will be -1. A subexpression 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 con-
		tained	within j, and a match of subexpression j is reported in pmatch[j], then the match or non-match of subexpression 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 character 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 pattern 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 new-
		line 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() associated 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 gener-
       ates 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 previous 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 generated 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 regular 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  indi-
       cate 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 expression 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 ALSO

       fnmatch(3C), glob(3C), malloc(3C), setlocale(3C), attributes(5), standards(5), regex(5)

NOTES

       The regcomp() function can be used safely in a multithreaded application as long as setlocale(3C) is not being called to change the locale.

SunOS 5.10							    1 Nov 2003							       regcomp(3C)