Microsoft KB Archive/168936

= FIX: Virtual Base Class Destructor Called More than Once =

Article ID: 168936

Article Last Modified on 7/5/2005

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APPLIES TO


 * Microsoft Visual C++ 5.0 Professional Edition
 * Microsoft Visual C++ 5.0 Enterprise Edition
 * Microsoft Visual C++ 4.2 Professional Edition
 * Microsoft Visual C++ 4.2 Enterprise Edition
 * Microsoft Visual C++ 4.1 Subscription
 * Microsoft Visual C++ 4.0 Standard Edition

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This article was previously published under Q168936



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:

132893 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.



Steps to Reproduce Behavior
//compiler options needed /GX

#include    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

Keywords: kbbug kbfix kbvc600fix kbcpponly kbcompiler KB168936

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