The isspace function tests for any character that is a standard white space character or is one of an implementation-defined set of characters for which isalnum is false. The standard white space characters are the following: space (' '), form feed ('\f'), new_line ('\n'), carriage return ('\r'), horizontal tab ('\t'), and vertical tab ('\v'). In the "C" locale, isspace returns true only for standard white space characters.