advance() — Pattern match given a compiled regular expression

Standards

Standards / Extensions	C or C++	Dependencies
XPG4 XPG4.2	both

Format

#define _XOPEN_SOURCE
#include <regexp.h>

int advance(const char *string, const char *expbuf);

extern char *loc2, *locs;

General description

Restriction: This function is not supported in AMODE 64.

The advance() function attempts to match an input string of characters with the compiled regular expression which was obtained by an earlier call to compile().

The first parameter string is a pointer to a string of characters to be checked for a match.

expbuf is the pointer to the regular expression which was previously obtained by a call to compile().

The external variable loc2 will point to the next character in string after the last character that matched the regular expression.

The external variable locs can be optionally set to point to some point in the input regular expression string to cause the advance() function to exit its back up loop.

Note: The external variables cirf, sed, and nbra are reserved.

During the pattern matching operation, when advance() encounters a * or \{\} sequence in the regular expression, it will advance its pointer to the string to be matched as far as possible and will recursively call itself trying to match the rest of the string to the rest of the regular expression. As long as there is no match, advance() will back up along the string until it finds a match or reaches the point in the string that initially matched the * or \{\}. It is sometime desirable to stop this backing up before the initial point in the string is reached. If the external character pointer locs is equal to the point in the string at some time during the back up process, advance() will break out of the loop that backs up and will return 0 (a failure indication).

Notes:

The application must provide the proper serialization for the compile(), step(), and advance() functions if they are run under a multithreaded environment.
The compile(), step(), and advance() functions are provided for historical reasons. These functions were part of the Legacy Feature in Single UNIX Specification, Version 2. They have been withdrawn and are not supported as part of Single UNIX Specification, Version 3. New applications should use the newer functions fnmatch(), glob(), regcomp() and regexec(), which provide full internationalized regular expression functionality compatible with IEEE Std 1003.1-2001.

Returned value

If the initial substring of string matches the regular expression in expbuf, advance() returns nonzero.

If there is no match, advance() returns 0.

If there is a match, advance() sets an external character pointer, loc2, as a side effect. The variable loc2 points to the next character in string after the last character that matched the regular expression.