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Q59399: BASIC 7.0 UEVENT Example Causes Subsequent Programs to Hang

Article: Q59399
Product(s): See article
Version(s): m7.00 7.10
Operating System(s): MS-DOS
Keyword(s): ENDUSER | SR# S900222-46 docerr buglist7.00 buglist7.10 | mspl13_basic
Last Modified: 20-SEP-1990

The sample program for trapping a user-defined event on Pages 310-312
of the "Microsoft BASIC 7.0: Programmer's Guide" for Microsoft BASIC
Professional Development System (PDS) versions 7.00 and 7.10 contains
a misprint, but even if corrected, this sample program may cause the
computer to hang after it is run.

Microsoft has confirmed this to be a problem in Microsoft BASIC
Professional Development System (PDS) versions 7.00 and 7.10. We are
researching this problem and will post new information here as it
becomes available.

Page 311 of "Microsoft BASIC 7.0: Programmer's Guide" contains a
misprint in the MASM programming example for trapping a user-defined
event. If the code is not corrected, an "A2009: Symbol not defined"
error will result when the code is assembled.

The last section of code for this example reads as follows:

    RestInt  proc  uses ds
       lds dx, cs:OldVector
       mov  x, 251CH          ; <== this line contains the misprint

To correct the code, make the following change:

    RestInt  proc  uses ds
       lds dx, cs:OldVector
       mov ax, 251CH          ; <== change "x" to "ax"

However, even when this misprint is corrected, if the BASIC program is
compiled so that it requires a run-time module or if the assembly code
is put into a Quick library, running the program may cause the
computer to hang. The problem does not occur if the BASIC program is
compiled with the BC /O option.

The following compiling and linking steps will reproduce the problem:

1. Assemble the MASM code as follows:

      MASM MASMPROG.ASM;

2. Compile the BASIC code so that it requires a run-time module (no
   /O) and enables event trapping (/V). If the program is compiled as
   a stand-alone program (with the /O option), the problem does not
   exist.

      BC BASPROG.BAS /V;

3. LINK the program using the BASIC PDS 7.00 or 7.10 linker, as
   follows:

      LINK BASPROG.OBJ + MASMPROG.OBJ;

4. Run the program.

5. The computer may hang instantly or may hang after attempting to run
   another program, such as QBX.EXE.

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