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 strspn()                Find First Substring

 #include   <string.h>                   Required for declarations only

 size_t     strspn(string1,string2);
 const char *string1;                    Searched string
 const char *string2;                    Character set

    strspn() tests whether the first substring (i.e., the substring
    beginning at the start of 'string1') in 'string1' consists entirely
    of characters from character set 'string2'.  (It does this by
    searching 'string1' for the first occurrence of a character that is
    not also in 'string2'.)

       Returns:     The index in 'string1' of the first character past
                    the substring that contains only characters from
                    'string2'. This is equal to the first character in
                    'string1' that is not among the characters in
                    'string2'.  Looking at it another way, the index
                    value is equal to the length of the substring of
                    'string1' that is made up of characters from
                    'string2'.

   -------------------------------- Example ---------------------------------

    The following statements check whether 'string' begins with a vowel.

           #include <string.h>

           int rslt;
           char *string = "imagination";
           char *charset = "aeiou";

           main()
           {
               if((rslt = strspn(string,charset)) > 0)
                  printf("string begins with a vowel\n");
           }