Q32274: Do Not Use DOS Interrupts to Terminate Compiled Programs

Article: Q32274
Product(s): See article
Version(s): 4.00 4.00b 4.50
Operating System(s): MS-DOS
Keyword(s): ENDUSER | B_BasicCom | mspl13_basic
Last Modified: 21-DEC-1989

The following information applies to QuickBASIC Versions 4.00, 4.00b
and 4.50, to Microsoft BASIC Compiler Versions 6.00 and 6.00b for
MS-DOS and MS OS/2, and to Microsoft BASIC PDS Version 7.00 for MS-DOS
and MS OS/2.

Some DOS interrupts should not be invoked from QuickBASIC programs.
For example, "Terminate With Return Code" (Interrupt 21H, function
4CH) can cause loss of the cursor the first time it is executed, then
a hard hang on a subsequent CALL.

QuickBASIC must control its own termination to correctly return to
DOS. Please use the END statement in BASIC rather than a DOS interrupt
to terminate a program.

The following is a code example:

'WARNING:
'Execution of the following code will result in unpredictable results,
'such as system lockup or loss of the DOS cursor in some instances.
DIM inarray%(7), outarray%(7)
inarray%(0) = &H4C00
CALL int86old(&H21, inarray%(), outarray%())
'The INT86OLD routine is located in QB.QLB and QB.LIB.

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