Thanks! I tried using it but the compiler fails to recognize this function. Is it present in the stdlib?

Is the usage like,
check_flag = find_first_not_of(abc) ;
//where to I give the string...

If your input is "abc". What would be the logic to accept the strings, bca,acb,bac,cab,cba,abc (ie. the same string with chars placed in any order)
and reject all other input strings like aab, cdb,...