### 3.4 `iscntrl`—control character predicate

Synopsis

         #include <ctype.h>
         int iscntrl(int c);

Description
`iscntrl` is a macro which classifies ASCII integer values by table lookup. It is a predicate returning non-zero for control characters, and 0 for other characters. It is defined only when `isascii`(c) is true or c is EOF.

You can use a compiled subroutine instead of the macro definition by undefining the macro using ``#undef iscntrl`'.

Returns
`iscntrl` returns non-zero if c is a delete character or ordinary control character (`0x7F` or `0x00`–`0x1F`).

Portability
`iscntrl` is ANSI C.

No supporting OS subroutines are required.