setbuf() Doesn't Control MS-DOS Buffer or Keyboard Buffer

MS-DOS                      | WINDOWS

The information in this article applies to:

• The C Run-time (CRT), included with:

      - Microsoft C for MS-DOS, versions 5.1, 6.0, 6.0a, and 6.0ax
      - Microsoft C for OS/2, versions 5.1, 6.0, and 6.0a
      - Microsoft C/C++ for MS-DOS, version 7.0
      - Microsoft Visual C++ for Windows, versions 1.0 and 1.5
  

SUMMARY

The getchar() function will wait for a carriage return even if setbuf() is used to unbuffer stdin.

MORE INFORMATION

The function setbuf() affects a stream file buffer, such as stdin, but has no effect on the keyboard or MS-DOS device buffers. The stream I/O function getchar() can read a character from the keyboard buffer only when the keyboard buffer is flushed by either being filled, by a carriage return, or by an interrupt 0x21, function 0xC call.

To read normal characters directly from the keyboard, you can use the console I/O function getch(). To read control codes such as ALT+Q (echo subsequent output to printer) or ALT+R (pause output), you can use the _bios_keybrd() function. For more information on this function, query on the following word in the Microsoft Knowledge Base:

   _bios_keybrd()

Sample Code

/* Compile options needed: none
*/

#include <stdio.h>
#include <conio.h>

void main (void)

   setbuf (stdin, NULL);        /* cause stdin to be unbuffered */
   if (getchar () != EOF )
      printf ("getchar() still waits for return key\n");
   if (getch () != EOF )
      printf ("getch() does not wait for return key\n");