Q45563: setbuf() Doesn’t Control MS-DOS Buffer or Keyboard Buffer

Article: Q45563
Product(s): Microsoft C Compiler
Version(s): winnt:
Operating System(s): 
Keyword(s): kb16bitonly
Last Modified: 22-JUL-2001

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

The following example demonstrates the difference between using getchar() and
getch().

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");
  }

Additional query words: kbinf 1.00 1.50 5.10 6.00 6.00a 6.00ax 7.00

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Keywords          : kb16bitonly 
Technology        : kbVCsearch kbAudDeveloper kbCRT
Version           : winnt:

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