Knowledge Base

FIX: Debugger Cannot Watch Function Returning struct or union

Article ID: 177937

Article Last Modified on 12/2/2003

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

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:

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;
       }

Build the project.
Click Build|Start Debug|Step Into on the Developer Studio menu.
Goto the Watch window by selecting View|Debug Windows|Watch.
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