Compares the characters in a wide-character string against a
    set of wide characters. The function returns the length of the
    initial substring that is comprised entirely of characters that
    are not in the set of wide characters.

    Format

      #include  <wchar.h>

      size_t wcscspn  (const wchar_t *wstr1, const wchar_t *wstr2);

1 - Arguments

 wstr1

    A pointer to a null-terminated wide-character string. If this is
    a null string, 0 is returned.

 wstr2

    A pointer to a null-terminated wide-character string that
    contains the set of wide characters for which the function will
    search.

2 - Description

    The wcscspn function scans the wide characters in the string
    pointed to by wstr1 until it encounters a character found in
    wstr2. The function returns the length of the initial segment of
    wstr1 that is formed by characters not found in wstr2.

3 - Return Value

    x                  The length of the segment.

4 - Example

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

        /* This test sets up 2 strings, buffer and w_string, and */
        /* then uses wcscspn() to calculate the maximum segment  */
        /* of w_string, which consists entirely of characters    */
        /* NOT 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, "jklmabcjklabcdehjklmno", STRING_SIZE)

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

        /* Using wcscspn - work out the largest string in w_string */
        /* which consists entirely of characters NOT from buffer   */

            result = wcscspn(w_string, buffer);
            printf("Longest segment NOT found in w_string is: %d", result);

        }

    Running the example program produces the following result:

    Longest segment NOT found in w_string is: 4