Returns the length of the prefix of a string that consists
    entirely of characters not in a specified set of characters.

    Format

      #include  <string.h>

      size_t strcspn  (const char *str, const char *charset);

1 - Arguments

 str

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

 charset

    A pointer to a character string containing the set of characters.

2 - Description

    This function scans the characters in the string, stops when it
    encounters a character found in charset, and returns the length
    of the string's initial segment formed by characters not found in
    charset.

    If none of the characters match in the character strings pointed
    to by str and charset, strcspn returns the length of string.

3 - Return Value

    x                  The length of the segment.