BUG: this Pointer Expands Incorrectly for Multiple Inheritance

The information in this article applies to:

• Microsoft CodeView for MS-DOS, version 4.1
• Microsoft CodeView for Windows, version 4.1
• The integrated debugger included with:

        - Microsoft Visual C++ for Windows, versions 1.0, 1.5, 1.51, and 1.52
  

SYMPTOMS

Expanding the "this" pointer of a class with multiple inheritance displays incorrect information.

CAUSE

The class type is derived from more than one classes.

STATUS

Microsoft has confirmed this to be a problem in Microsoft CodeView version 4.1 for MS-DOS and Windows and in the Visual Workbench Debugger that ships with Visual C++ for Windows, version 1.0.

The problem does not occur with the Visual Workbench Debugger that ships with Visual C++ 32-bit Edition or with CodeView for Win32s version 4.25.

MORE INFORMATION

When you debug the sample code below, expanding the this pointer of the class collection in a Watch window displays the following:

-this = 0x45CA:0x09A2

  -base1 = {...}
    -base1 = CXX0030: Error: expression cannot be evaluated
      +base1 = CXX0030: Error: expression cannot be evaluated
      +base2 = CXX0030: Error: expression cannot be evaluated
       c = CXX0030: Error: expression cannot be evaluated
    -base2 = CXX0030: Error: expression cannot be evaluated
      +base1 = CXX0030: Error: expression cannot be evaluated
      +base2 = CXX0030: Error: expression cannot be evaluated
       c = CXX0030: Error: expression cannot be evaluated
     c = CXX0030: Error: expression cannot be evaluated
  -base2 = {...}
    +base1 = CXX0030: Error: expression cannot be evaluated
    +base2 = CXX0030: Error: expression cannot be evaluated
     c = CXX0030: Error: expression cannot be evaluated
   c = 12870

Sample Code

/*
 * Compiler options needed: /Zi /Od
 */

   public:
   int a;

class base2{

   public:
   int b;

class collection:public base1,public base2 {

   public:
   int c;
   void sub();

void collection::sub()

   a=100;  // Set a breakpoint here and watch this pointer.
   b=200;
   c=300;

void main()

   collection k;
   k.sub();