PCRE - Perl-compatible regular expressions
pcre_extra *pcre_study(const pcre *code, int options, const char **errptr);
This function studies a compiled pattern, to see if additional information can be extracted that might speed up matching. Its arguments are:
code A compiled regular expression
options Options for pcre_study()
errptr Where to put an error message
If the function succeeds, it returns a value that can be passed to pcre_exec() via its extra argument.
If the function returns NULL, either it could not find any additional information, or there was an error. You can tell the difference by looking at the error value. It is NULL in first case.
There are currently no options defined; the value of the second argument should always be zero.
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.