FIX: Debugger Cannot Watch Function Returning struct or union (177937)


The information in this article applies to:

  • The Integrated Debugger, when used with:
    • Microsoft Visual C++, 32-bit Enterprise Edition 5.0
    • Microsoft Visual C++, 32-bit Enterprise Edition 6.0
    • Microsoft Visual C++, 32-bit Professional Edition 5.0
    • Microsoft Visual C++, 32-bit Professional Edition 6.0
    • Microsoft Visual C++, 32-bit Learning Edition 6.0
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.
Modification Type:MajorLast Reviewed:12/2/2003
Keywords:kbBug kbDebug kbfix kbide kbNoUpdate KB177937
©2003 Microsoft Corporation. All rights reserved.