Q58213: How to Empty (Flush) the Keyboard Buffer in BASIC

Article: Q58213
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900118-69 B_BasicCom | mspl13_basic
Last Modified: 7-FEB-1990

The two programs below show two different methods of emptying the
keyboard input buffer. The first program uses a DOS interrupt to clear
the buffer, while the second program uses the INKEY$ function.

This information applies to Microsoft QuickBASIC Versions 4.00, 4.00b,
and 4.50 for MS-DOS; to Microsoft BASIC Compiler Versions 6.00 and
6.00b for MS-DOS; and to Microsoft BASIC Professional Development
System (PDS) Version 7.00 for MS-DOS.

Code Example 1
--------------

The following program uses DOS interrupt 21 hex (33 decimal) with
function 0C hex (12 decimal), which flushes the input (type-ahead)
keyboard buffer. To run this program inside the QuickBASIC (QB.EXE)
environment, you must load the Quick library QB.QLB with the /L
option. To run this program inside the QuickBASIC Extended (QBX.EXE)
environment supplied with Microsoft BASIC PDS Version 7.00, load the
Quick library QBX.QLB with the /L option.

   'For BASIC PDS Version 7.00 you must instead use $INCLUDE: 'QBX.BI'
   REM $INCLUDE: 'qb.bi'
   DIM inregs AS regtype
   DIM outregs AS regtype
   inregs.ax = &HC00   ' 0C hex goes in AH, high byte of AX register
                       ' 00 goes in AL, the low byte of AX register
   CALL INTERRUPT(&H21, inregs, outregs)
   END

Code Example 2
--------------

The following program uses the INKEY$ function to read characters from
the keyboard buffer until no more are available. This program can also
be used under MS OS/2 protected mode when compiled with Microsoft
BASIC Compiler Versions 6.00 and 6.00b and Microsoft BASIC PDS Version
7.00.

   WHILE INKEY$ <> ""
   WEND

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