Example

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

       /* This test sets up 2 strings, buffer and w_string. It */
       /* then uses wcsspn() to calculate the maximum segment  */
       /* of w_string that consists entirely of characters     */
       /* from buffer.                                         */

       #define BUFF_SIZE 20
       #define STRING_SIZE 50

       main()
       {
           wchar_t buffer[BUFF_SIZE];
           wchar_t w_string[STRING_SIZE];
           size_t result;

           /* Initialize the buffer */

           if (mbstowcs(buffer, "abcdefg", BUFF_SIZE) == (size_t)-1) {

               perror("mbstowcs");
               exit(EXIT_FAILURE);
           }

           /* Initialize the string */

           if (mbstowcs(w_
string, "abcedjklmabcjklabcdehjkl", STRING_SIZE)

               == (size_t)-1) {

               perror("mbstowcs");
               exit(EXIT_FAILURE);
           }

       /* Using wcsspn - work out the largest string in w_string */
       /* that consists entirely of characters from buffer       */

           result = wcsspn(w_string, buffer);
           printf("Longest segment found in w_
string is: %d", result);

       }

   Running the example program produces the following result:

   Longest segment found in w_string is: 5