FIX: Call to Member Function with Virtual Base Fails

The information in this article applies to:

• The Microsoft C/C++ Compiler (CL.EXE), included with:

      - Microsoft Visual C++ for Windows, version 1.0
  

SYMPTOMS

The use of the /Ob2, /Oe, and /Og optimization switches may cause calls to a member function of a class with a virtual base class to return incorrect values.

RESOLUTION

There are several workarounds to this problem:

1. Use the /Ob1 optimization instead of /Ob2

   -or-

2. Use the fast compiler option /f.

   -or-

3. Disable optimization by either removing the /Oe and /Og switches.

   -or-

4. Disable optimization locally using the optimize pragma:

         #pragma optimize("",off)
   

         void classname::classfunction()
         {
         }
   

         #pragma optimize("",on)
   

STATUS

Microsoft has confirmed this to be a problem in the Microsoft products listed above. This is not a problem in Visual C++, 32-bit Edition. This problem was corrected in Visual C++ version 1.5.

MORE INFORMATION

The sample code below can be used to illustrate this problem.

Sample Code

/* Compile options needed: /Ob2 /AC (or /AL or /AH)
*/

#include <stdio.h>
#include <stdlib.h>

 public:
   int a;
   int b;
   int z;
   int funcA(int);

int A::funcA(int i)

   return a + b + i;

class B : virtual public A {

 public:
   int c;
   int d;
   int z;
   int funcA(int);
   int funcB(int);

int B::funcA(int i)

   return a + c + i;

int B::funcB(int i)

   return c + d + i;

void main(void)

   A a; a.a = 1; a.b = 2;
   B b; b.a = 1; b.b = 2; b.c = 3; b.d = 4;

   if (a.funcA(1) != 4) printf("FAILED on line %d\n", __LINE__);

   \\ Error occurs on this line
   if (b.funcA(1) != 5) printf("FAILED on line %d\n", __LINE__);

   if (b.funcB(1) != 8) printf("FAILED on line %d\n", __LINE__);

   return 0;