scan_xlonglong man page
scan_xlonglong — parse an unsigned long long integer in hexadecimal ASCII representation
size_t scan_xlonglong(const char *src,unsigned long long* dest);
scan_xlonglong parses an unsigned long long integer in hexadecimal ASCII representation from src and writes the result into dest. It returns the number of bytes read from src.
scan_xlonglong understands both upper and lower case letters.
scan_xlonglong does not expect or understand a "0x" prefix.