Microsoft KB Archive/177937

Knowledge Base

FIX: Debugger Cannot Watch Function Returning struct or union

Article ID: 177937

Article Last Modified on 12/2/2003

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APPLIES TO

• The Integrated Debugger, when used with:
  • Microsoft Visual C++ 5.0 Enterprise Edition
  • Microsoft Visual C++ 6.0 Enterprise Edition
  • Microsoft Visual C++ 5.0 Professional Edition
  • Microsoft Visual C++ 6.0 Professional Edition
  • Microsoft Visual C++ 6.0 Standard Edition

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This article was previously published under Q177937

SYMPTOMS

Adding a function call in the Developer Studio debugger Watch window may result in the following message if the function returns a struct or union with a field width greater than 4 bytes:

Error: cannot display value

RESOLUTION

There is no workaround for this problem.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

This problem was corrected in Microsoft Visual C++ .NET.

MORE INFORMATION

The following procedure reproduces this problem:

1. Create a new console application project and add the following file to the project:

         /* File: TEST.CPP */ 
   
          struct _XX
              {
              char   m1;
              char   m2;
              char   m3;
              char   m4;
              } XX;
   
          struct _XX fun()
          {
              return XX;
          }
   
          int main()
          {
              fun();
              return 0;
          }
                           

2. Build the project.
3. Click Build|Start Debug|Step Into on the Developer Studio menu.
4. Goto the Watch window by selecting View|Debug Windows|Watch.
5. Add the following watch expression in the "Name" column: fun()

Results: You will see the message "Error: cannot display value" in the "Value" column.

Keywords: kbbug kbfix kbnoupdate kbide kbdebug KB177937

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