Q40888: RUN and execlp Between QB 4.00 and C Can Dump to DOS

Article: Q40888
Product(s): See article
Version(s): 4.00
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S890124-94 buglist4.00 fixlist4.00b fixlist4.50 | mspl13_basic
Last Modified: 17-FEB-1989

When transferring control back and forth between a Microsoft
QuickBASIC Version 4.00 compiled program (using the RUN statement) and
a Microsoft C program (using the execlp routine), the C program can
dump itself to MS-DOS. The following are the conditions necessary for
this behavior to occur:

1. The QuickBASIC program RUNs a C program with the RUN statement.

2. The Microsoft C program invokes the execlp routine to transfer
   control back to the QuickBASIC program.

3. The QuickBASIC program RUNs the C program again. At this point,
   the Microsoft C program aborts to MS-DOS.

The error only occurs when QuickBASIC is the starting program. If C
started the process, the transfer of control continues correctly back
and forth without aborting.

Microsoft has confirmed this to be a problem in Version 4.00. This
problem was corrected in Version 4.00b (and 4.50).

Below is the QuickBASIC example code, BEXAMPLE.BAS:

' Compile and LINK as follows:  BC /O BEXAMPLE;
'                               LINK BEXAMPLE;
CLS
PRINT "Inside the BASIC Program."
FOR i = 1 TO 1000: NEXT i          ' Do nothing loop to take up time
PRINT "Calling C."
FOR i = 1 TO 1000: NEXT i          ' Do nothing loop to take up time
RUN "CEXAMPLE"                     ' Calls the C Program
END

Below is the C example code, CEXAMPLE.C:

/*
   Compile and LINK as follows:  CL /lib/graphics CEXAMPLE.C
*/
#include <stdio.h>
#include <graph.h>
#include <process.h>
main()
{
_clearscreen(_GCLEARSCREEN);
printf("In The C Program.....Hit RETURN To Continue");
getchar();
_clearscreen(_GCLEARSCREEN);
execlp("BEXAMPLE.EXE",NULL);             /* Calls the QB Program */
}

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