pcre2_substring_copy_byname man page
PCRE2 — Perl-compatible regular expressions (revised API)
int pcre2_substring_copy_byname(pcre2_match_data *match_data, PCRE2_SPTR name, PCRE2_UCHAR *buffer, PCRE2_SIZE *bufflen);
This is a convenience function for extracting a captured substring, identified by name, into a given buffer. The arguments are:
match_data The match data block for the match
name Name of the required substring
buffer Buffer to receive the string
bufflen Length of buffer (code units)
The bufflen variable is updated to contain the length of the extracted string, excluding the trailing zero. The yield of the function is zero for success or one of the following error numbers:
PCRE2_ERROR_NOSUBSTRING there are no groups of that name
PCRE2_ERROR_UNAVAILBLE the ovector was too small for that group
PCRE2_ERROR_UNSET the group did not participate in the match
PCRE2_ERROR_NOMEMORY the buffer is not big enough
If there is more than one group with the given name, the first one that is set is returned. In this situation PCRE2_ERROR_UNSET means that no group with the given name was set.
There is a complete description of the PCRE2 native API in the pcre2api page and a description of the POSIX API in the pcre2posix page.