PRB: Debugger Cannot Watch Global Constants in C++ Programs (115347)

The information in this article applies to:

Microsoft Visual Workbench for Windows, when used with:
- Microsoft Visual C++ 1.0
- Microsoft Visual C++, 32-bit Learning Edition 4.0
- Microsoft Visual C++, 32-bit Enterprise Edition 5.0
- Microsoft Visual C++, 32-bit Professional Edition 2.1
- Microsoft Visual C++, 32-bit Professional Edition 4.0
- Microsoft Visual C++, 32-bit Professional Edition 5.0
- Microsoft CodeView for MS-DOS 4.0
- Microsoft CodeView for MS-DOS 4.01
- Microsoft CodeView for MS-DOS 4.1
- Microsoft CodeView for Windows 4.0
- Microsoft CodeView for Windows 4.01
- Microsoft CodeView for Windows 4.1

This article was previously published under Q115347

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."

However, when global constants are used in a C++ program, they cannot be watched in a local or watch window with CodeView or the Integrated (IDE) Debugger in Visual C++.

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

Attempting to watch A using the Visual C++ for Windows version 1.0 or the Visual C++ 32-bit Edition version 1.0 or 2.1 IDE Debugger yields a dialog box with the following text:

Cannot watch 'A'.

Attempting to watch A using the Visual C++ 32-bit Edition version 4.0 IDE Debugger produces the following in the Watch window:

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

Sample Code

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

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

Modification Type:	Minor	Last Reviewed:	8/16/2005
Keywords:	kbBug kbDebug kbide kbprb KB115347