Q177937: FIX: Debugger Cannot Watch Function Returning struct or union

Article: Q177937
Product(s): Microsoft C Compiler
Version(s): 5.0,5.0sp1,5.0sp2,6.0
Operating System(s): 
Keyword(s): kbDebug kbide kbVC500bug kbVC600bug kbNoUpdate
Last Modified: 10-FEB-2002

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The information in this article applies to:

- The Integrated Debugger, used with:
   - Microsoft Visual C++, 32-bit Enterprise Edition, versions 5.0, 5.0sp1, 5.0sp2, 6.0 
   - Microsoft Visual C++, 32-bit Professional Edition, versions 5.0, 5.0sp1, 5.0sp2, 6.0 
   - Microsoft Visual C++, 32-bit Learning Edition, version 6.0 
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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.

Additional query words:

======================================================================
Keywords          : kbDebug kbide kbVC500bug kbVC600bug kbNoUpdate 
Technology        : kbVCsearch kbAudDeveloper kbIntegratedDebugger
Version           : :5.0,5.0sp1,5.0sp2,6.0
Issue type        : kbbug
Solution Type     : kbfix

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