pcre_study man page
PCRE — Perl-compatible regular expressions
pcre_extra *pcre_study(const pcre *code, int options, const char **errptr); pcre16_extra *pcre16_study(const pcre16 *code, int options, const char **errptr); pcre32_extra *pcre32_study(const pcre32 *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[16|32]_study()
errptr Where to put an error message
If the function succeeds, it returns a value that can be passed to pcre[16|32]_exec() or pcre[16|32]_dfa_exec() via their extra arguments.
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.
The only option is PCRE_STUDY_JIT_COMPILE. It requests just-in-time compilation if possible. If PCRE has been compiled without JIT support, this option is ignored. See the pcrejit page for further details.
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.