ID Number: Q43993
5.10 6.00 6.00a 6.00ax 7.00 | 5.10 6.00 6.00a
MS-DOS | OS/2
Summary:
To flush the BIOS keyboard typeahead buffer, the MS-DOS Interrupt 21
Function 0CH may be used. This function clears the keyboard typeahead
buffer and then invokes a reading function specified in the AL register.
The AL register can be 0x01, 0x06, 0x07, 0x08, or 0x0A to specify a
valid reading function. If you do not intend to read after flushing
the buffer, you may specify an invalid number in AL.
Another method of flushing the BIOS buffer is to call the console I/O
function getch() until the function kbhit() becomes false. This method
is demonstrated in the program below and has the advantage of being
usable under OS/2 as well as MS-DOS.
More Information:
The buffer implemented by the C run-time functions for the stream
"stdin" is different from the BIOS keyboard typeahead buffer. To clear
the buffer for stdin, use the function fflush(). However, this method
will not flush the BIOS buffer. To be totally flushed, you must both
flush the BIOS buffer as described above AND call fflush for stdin.
The following sample program is an example:
Sample Code
-----------
/* Compile options needed: none
*/
#include <stdio.h>
#include <time.h>
#include <conio.h>
#include <dos.h>
void main (void)
{
time_t start, work ;
char str [50] ;
puts ("type for getchar(). Go to stdin's buffer.") ;
// user can type more than one character and an Enter.
getchar () ;
puts ("Type fast, 5 seconds. Go to BIOS buffer.") ;
// user can type anything including multiple Enters.
time (&start) ;
work = start ;
while ( (work - start) < 5 ) time (&work) ;
bdos (0xC, 0, 0) ; // clear BIOS keyboard buffer
// Alternative method:
// while (kbhit()) getch();
fflush (stdin) ; // clear stdin's buffer
puts ("Should be waiting again.") ;
gets (str) ;
puts (str) ;
}
Additional reference words: 5.10 6.00 6.00a 6.00ax 7.00