DOCUMENT:Q168936  04-MAY-2001  [visualc]
TITLE   :FIX: Virtual Base Class Destructor Called More than Once
PRODUCT :Microsoft C Compiler
PROD/VER:winnt:4.0,4.1,4.2,5.0
OPER/SYS:
KEYWORDS:kbtool kbCompiler kbCPPonly kbVC kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600fix

======================================================================
-------------------------------------------------------------------------------
The information in this article applies to:

 - The C/C++ Compiler (CL.EXE), used with:
    - Microsoft Visual C++, 32-bit Editions, versions 4.0, 4.1 
    - Microsoft Visual C++, 32-bit Enterprise Edition, version 4.2 
    - Microsoft Visual C++, 32-bit Professional Edition, version 4.2 
    - Microsoft Visual C++, 32-bit Enterprise Edition, version 5.0 
    - Microsoft Visual C++, 32-bit Professional Edition, version 5.0 
-------------------------------------------------------------------------------

SYMPTOMS
========

If an exception is thrown from the constructor of a class that is derived from a
virtual base class, the destructor for the virtual base class is called more
than once. This doesn't happen if the exception is thrown from any other member
function.

RESOLUTION
==========

There is no workaround. Avoid throwing exceptions from the constructor.

For additional information about the two-phased construction, please see the
following article in the Microsoft Knowledge Base:

   Q132893 PRB: Exceptions Thrown During Construction Can Orphan Memory

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 Visual C++ version 6.0
for Windows.

MORE INFORMATION
================

Steps to Reproduce Behavior
---------------------------

      //compiler options needed  /GX

       #include <iostream.h>
       class A
       {
         public:
               A() { cout << "In A-ctor" << endl;}
               ~A(){ cout << "In A-dtor" << endl;}
       };

       class B1 : public  virtual   A
       {
         public:
                 B1() { cout << "In B1-ctor" << endl;}
               ~B1(){ cout << "In B1-dtor" << endl;}
       };

       class B2 : public  virtual  A
       {
         public:
                 B2() { cout << "In B2-ctor" << endl;}
               ~B2(){ cout << "In B2-dtor" << endl;}
       };

       class C : public B1 ,public B2
       {
         public:
             C(){
            cout << "In C-ctor...throw Exception" << endl;
            throw int(1); //incorrect destructor calls...
                }

             ~C(){ cout << "In C-dtor" << endl;}
       };

       void main()
       {
         try
          {
            C c;

          }
         catch (int ex)
          {
            cout << "Caught Exception #" << ex << endl;
            }
       }

The program output is:

   In A-ctor
   In B1-ctor
   In B2-ctor
   In C-ctor...throw Exception
   In B2-dtor
   In A-dtor
   In B1-dtor
   In A-dtor
   In A-dtor
   Caught Exception #1

The expected output is:

   In A-ctor
   In B1-ctor
   In B2-ctor
   In C-ctor...throw Exception
   In B2-dtor
   In B1-dtor
   In A-dtor
   Caught Exception #1

Additional query words:

======================================================================
Keywords          : kbtool kbCompiler kbCPPonly kbVC kbVC400bug kbVC410bug kbVC420bug kbVC500bug kbVC600fix 
Technology        : kbVCsearch kbAudDeveloper kbCVCComp
Version           : winnt:4.0,4.1,4.2,5.0
Issue type        : kbbug
Solution Type     : kbfix

=============================================================================

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Copyright Microsoft Corporation 2001.