PCRE2 - Perl-compatible regular expressions (revised API) .rs #include <pcre2.h>

 int pcre2_callout_enumerate(const pcre2_code *code,  " int (*callback)(pcre2_callout_enumerate_block *, void *),"  " void *callout_data);" 

. .rs This function scans a compiled regular expression and calls the callback() function for each callout within the pattern. The yield of the function is zero for success and non-zero otherwise. The arguments are: code Points to the compiled pattern callback The callback function callout_data User data that is passed to the callback The callback() function is passed a pointer to a data block containing the following fields (not necessarily in this order): uint32_t version Block version number uint32_t callout_number Number for numbered callouts PCRE2_SIZE pattern_position Offset to next item in pattern PCRE2_SIZE next_item_length Length of next item in pattern PCRE2_SIZE callout_string_offset Offset to string within pattern PCRE2_SIZE callout_string_length Length of callout string PCRE2_SPTR callout_string Points to callout string or is NULL The second argument passed to the callback() function is the callout data that was passed to pcre2_callout_enumerate(). The callback() function must return zero for success. Any other value causes the pattern scan to stop, with the value being passed back as the result of pcre2_callout_enumerate().

There is a complete description of the PCRE2 native API in the HREF
pcre2api
page and a description of the POSIX API in the HREF
pcre2posix
page.