BUG: The "this" Pointer Is Incorrect in Destructor of Base Class

• Microsoft Visual C++, 32-bit Editions, versions 5.0, 6.0

SYMPTOMS

The "this" pointer is incorrectly set up in the destructor of a base class. This problem occurs when the array delete is called and there is a class that inherits from two base classes that have virtual functions and the second base class has a virtual destructor.

RESOLUTION

One workaround is to make the base classes virtual base classes. Another option is to use something other than array new and array delete to allocate and deallocate the memory. For example, declare the array statically.

STATUS

Microsoft has confirmed this to be a bug in the Microsoft products listed at the beginning of this article.

MORE INFORMATION

The following is example code:

   #include <iostream>
       using namespace std;
       class A {
       public:
          A(){}
          ~A(){}
          virtual void A1() {}
       };

       class B {
       public:
          B();
          virtual ~B();
          int marker;
       };

       B::B() {
          marker = 10;
          cout << "In constructor, this is " << this << endl;
       }

       B::~B() {
          cout << "In destructor, this is " << this << endl;
          if ( this->marker != 10)
             cout << "Data has been corrupted" << endl;
       }

       class C: public A, public B
       // class C: public A, virtual public B // Workaround
       {public:
          C(){}
          ~C(){}
       };

       int main() {
          C * pC;
          pC = new C[2];
          delete [] pC;
               return 0 ;
       }

   /* Sample Program Output */ 
   In constructor, this is 00460DA8
   In constructor, this is 00460DB4
   In destructor, this is 00460DB0
   Data has been corrupted
   In destructor, this is 00460DA4
   Data has been corrupted 

Additional query words:

Keywords : kbtool kbCompiler kbVC500bug kbVC600bug
Version : winnt:5.0,6.0
Platform : winnt
Issue type : kbbug