Technical Reference: Base Operating System and Extensions, Volume 2

regcomp Subroutine

Purpose

Compiles a specified basic or extended regular expression into an executable string.

Library

Standard C Library (libc. a)

Syntax

#include <regex.h>

int regcomp ( Preg, Pattern, CFlags) const char *Preg; const char *Pattern; int CFlags;

Description

The regcomp subroutine compiles the basic or extended regular expression specified by the Pattern parameter and places the output in the structure pointed to by the Preg parameter.

Parameters

Preg	Specifies the structure to receive the compiled output of the regcomp subroutine.
Pattern	Contains the basic or extended regular expression to be compiled by the regcomp subroutine. The default regular expression type for the Pattern parameter is a basic regular expression. An application can specify extended regular expressions with the REG_EXTENDED flag.
CFlags	Contains the bitwise inclusive OR of 0 or more flags for the regcomp subroutine. These flags are defined in the regex.h file: REG_EXTENDED Uses extended regular expressions. REG_ICASE Ignores case in match. REG_NOSUB Reports only success or failure in the regexec subroutine. If this flag is not set, the regcomp subroutine sets the re_nsub structure to the number of parenthetic expressions found in the Pattern parameter. REG_NEWLINE Prohibits . (period) and nonmatching bracket expression from matching a new-line character. The `^` (circumflex) and $ (dollar sign) will match the zero-length string immediately following or preceding a new-line character.

Return Values

If successful, the regcomp subroutine returns a value of 0. Otherwise, it returns another value indicating the type of failure, and the content of the Preg parameter is undefined.

Error Codes

The following macro names for error codes may be written to the errno global variable under error conditions:

REG_BADPAT	Indicates a basic or extended regular expression that is not valid.
REG_ECOLLATE	Indicates a collating element referenced that is not valid.
REG_ECTYPE	Indicates a character class-type reference that is not valid.
REG_EESCAPE	Indicates a trailing `\` in pattern.
REG_ESUBREG	Indicates a number in `\digit` is not valid or in error.
REG_EBRACK	Indicates a `[]` imbalance.
REG_EPAREN	Indicates a `` or `()` imbalance.
REG_EBRACE	Indicates a `\{\}` imbalance.
REG_BADBR	Indicates the content of `\{\}` is unusable: not a number, number too large, more than two numbers, or first number larger than second.
REG_ERANGE	Indicates an unusable end point in range expression.
REG_ESPACE	Indicates out of memory.
REG_BADRPT	Indicates a ? (question mark), * (asterisk), or + (plus sign) not preceded by valid basic or extended regular expression.

If the regcomp subroutine detects an illegal basic or extended regular expression, it can return either the REG_BADPAT error code or another that more precisely describes the error.

Examples

The following example illustrates how to match a string (specified in the string parameter) against an extended regular expression (specified in the Pattern parameter):

#include <sys/types.h>
#include <regex.h>
int
match(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);
}

In the preceding example, errors are treated as no match. When there is no match or error, the calling process can get details by calling the regerror subroutine.

Related Information

The regerror (regerror Subroutine) subroutine, regexec (regexec Subroutine) subroutine, regfree (regfree Subroutine) subroutine.

Subroutines Overview and Understanding Internationalized Regular Expression Subroutines in AIX 5L Version 5.2 General Programming Concepts: Writing and Debugging Programs.