#include <pcre.h>
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 yield 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 API in the pcreapi page.