These macros return a value other than 0 if the value of argument c matches the respective description (i.e., if the result is true). If the result is false, 0 is returned.
This function is a macro that checks whether a given character is an ASCII code (0x00 to 0x7F). This macro is defined for all integer values. A compiled subroutine can be used instead of the macro definition, which is invalidated by using "#undef isascii".