PCRE - Perl-compatible regular expressions
int pcre_get_substring(const char *subject, int *ovector, int stringcount, int stringnumber, const char **stringptr);
This is a convenience function for extracting a captured substring. The arguments are:
subject Subject that has been successfully matched
ovector Offset vector that pcre_exec() used
stringcount Value returned by pcre_exec()
stringnumber Number of the required substring
stringptr Where to put the string pointer
The memory in which the substring is placed is obtained by calling pcre_malloc(). The yield of the function is the length of the substring, PCRE_ERROR_NOMEMORY if sufficient memory could not be obtained, or PCRE_ERROR_NOSUBSTRING if the string number is invalid.
There is a complete description of the PCRE native API in the pcreapi page and a description of the POSIX API in the pcreposix page.