BUG: Screen Corruption Can Occur with _setvideomode()

The information in this article applies to:

• Microsoft CodeView for MS-DOS, versions 4.0, 4.01, and 4.1

SYMPTOMS

When the CodeView video mode is set to be the same as the current MS-DOS video mode, calls to _setvideomode(_DEFAULTMODE) can cause screen corruption.

RESOLUTION

To work around the problem, start CodeView in a different mode than the one MS-DOS is using.

STATUS

Microsoft has confirmed this to be a bug with CodeView for MS-DOS. We are researching this problem and will post new information in the Microsoft Knowledge Base as it becomes available.

MORE INFORMATION

The sample code below demonstrates the problem. Build a debug version and follow these steps:

1. Install the ANSI.SYS driver. If ANSI.SYS is not already installed, you have to reboot your computer to install it. To install ANSI.SYS, add the following line to your CONFIG.SYS file:

         DEVICE=C:\DOS\ANSI.SYS
   

2. Enter "mode co80, 50" at the MS-DOS prompt.

3. Enter "CV /50 VIDEO" to debug the VIDEO.EXE file in CodeView.

4. Type "t3" in the CodeView command window.

NOTE: Reissuing the mode command with different mode values at the MS-DOS prompt restores the screen.

In step 2 above, using "CV /43 video" or "CV /25 video" (without the quotes) prevents this problem from occurring.

Sample Code

/* Compile options needed: Zi /Od
*/

/* VIDEO.C */

   #include <graph.h>

   void main(void)
   {
    _setvideomode(_DEFAULTMODE);
   }