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 iscntrl()               Test for Control Character (Macro)

 #include   <ctype.h>

 int        iscntrl(c);
 int        c;                           Integer value to be tested

    iscntrl() is a macro that tests if 'c' is a control character; that
    is, if it is in the range 0 - 31 or 127 (0x00 - 0x1f or 0x7f).

    Returns:    True (nonzero) if the integer satisfies the test
                condition or false (zero) if it does not.  The result is
                undefined if 'c' is other than an ASCII character (c >
                127) or EOF.

      Notes:    iscntrl() is a macro.

                iscntrl() produces a defined result only where isascii()
                holds true or for the non-ASCII value EOF (defined in
                <stdio.h>).

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

    The following statements open a file and read in characters until a
    control character is read.

           #include <ctype.h>
           #include <stdio.h>              /* for fopen */

           FILE *stream;
           int ch;

           main()
           {
               if ((stream = fopen("input.dat","r+")) != NULL) {
                 .
                 .
               while (!iscntrl(ch = getc(stream)))
                      ;
             /* process ch */
                }
           }