Example

       #include <locale.h>
       #include <wchar.h>
       #include <stdio.h>
       #include <stdlib.h>
       #include <string.h>
       #include <ctype.h>

       /* This test will set up the "upper" character class using      */
       /* wctype() and then verify whether the characters 'a' and 'A'  */
       /* are members of this class                                    */

       #include <stdlib.h>

       main()
       {

           wchar_t w_char1,
                   w_char2;
           wctype_t ret_val;

           char *char1 = "a";
           char *char2 = "A";

           ret_val = wctype("upper");

           /* Convert char1 to wide-character format - w_char1 */

           if (mbtowc(&w_char1, char1, 1) == -1) {
              perror("mbtowc");
               exit(EXIT_FAILURE);
           }

           if (iswctype((wint_t) w_char1, ret_val))
               printf("[%C] is a member of the character class upper\n",
                       w_char1);
           else
            printf("[%C] is not a member of the character class upper\n",
                     w_char1);

           /* Convert char2 to wide-character format - w_char2 */

           if (mbtowc(&w_char2, char2, 1) == -1) {
               perror("mbtowc");
               exit(EXIT_FAILURE);
           }

           if (iswctype((wint_t) w_char2, ret_val))
               printf("[%C] is a member of the character class upper\n",
                       w_char2);
           else
            printf("[%C] is not a member of the character class upper\n",
                       w_char2);
       }

     Running the example program produces the following result:

       [a] is not a member of the character class upper
       [A] is a member of the character class upper