Tests for a hexadecimal-digit character, including the digits 0-9 and the letters a to f (or A to F), in the local multibyte code set.
#include <ctype.h> int Lisxdigit ( const char *c);
(IN) Points to the character to be tested.
Returns a nonzero value when the argument is a hexadecimal digit. Otherwise, it returns zero.
The Lisxdigit function is a double-byte interface.