PRB: Debugger Cannot Watch Global Constants in C++ Programs

• The Visual Workbench Integrated Debugger included with: - Microsoft Visual C++ for Windows, version 1.0 - Microsoft Visual C++ 32-bit Edition, versions 1.0, 2.1, 4.0, 5.0
• Microsoft CodeView for MS-DOS, versions 4.0, 4.01, 4.1
• Microsoft CodeView for Windows, versions 4.0, 4.01, 4.1

SYMPTOMS

On page 17 in chapter 2 of the C++ Tutorial included in Microsoft C/C++, version 7.0 and Visual C++, version 1.0, it states:

   "Constants declared with const have an advantage over those defined by
   #define in that they are accessible to a symbolic debugger, making
   debugging easier."

RESOLUTION

The above behavior is by design in the products listed above. In these versions, with the exception of CodeView 4.25 for Win32S, only local constants are accessible to CodeView and the Visual C++ IDE debugger.

CAUSE

In Microsoft C++, storage of global constants is optimized for the purpose of saving space, therefore no debug information is generated.

MORE INFORMATION

When debugging the following C++ sample program with CodeView, attempting to watch the global const a yields the following error:

     A = CXX0030: Error: expression cannot be evaluated

     Cannot watch 'A'.

     A = CXX0017: Error: symbol "A" not found

Sample Code

   /* Compile options needed: /Zi /Od
   */

   const int A=100;
   void main()
   {
      int dummy=0;
      dummy++;
   }

Keywords          : CvwIss WBDebug
Version           : MS-DOS:4.0,4.01,4.1;WINDOWS:1.0,4.0,4.01,4.1;WINDOWS  NT:1.0,2.1,4.0,5.0
Platform          : MS-DOS NT WINDOWS
Issue type        : kbprb