Microsoft KB Archive/143082

= FIX: Wrong Pointer Value When Nested Classes Have Same Name =

Article ID: 143082

Article Last Modified on 7/5/2005

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APPLIES TO


 * Microsoft Visual C++ 2.0 Professional Edition
 * Microsoft Visual C++ 2.1
 * Microsoft Visual C++ 2.2
 * Microsoft Visual C++ 4.0 Standard Edition
 * Microsoft Visual C++ 4.1 Subscription
 * Microsoft Visual C++ 4.2 Enterprise Edition
 * Microsoft Visual C++ 4.2 Professional Edition
 * Microsoft Visual C++ 5.0 Enterprise Edition
 * Microsoft Visual C++ 5.0 Professional Edition

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This article was previously published under Q143082



SYMPTOMS
When a class is derived from multiple classes such that two or more of the base classes are nested classes of the same name, pointers to either of the nested base classes point to the same address. Consider a class D which is derived from both B1::Nested and B2::Nested. Given an object d, which is of type D, then (B1::Nested *)&d and (B2::Nested *)&d will both resolve to the same address. If either of the nested base class' names are changed to be unique, the behavior is normal.



RESOLUTION
This happens only when the nested classes have the same name. Change the names, for example "A::NestedA" and "B::NestedB".



STATUS
This bug was corrected in Microsoft Visual C++, version 6.0.



Sample Code to Reproduce Error
// Compile option needed: none

// File test.cpp

truct A {

struct Nested { virtual void A_Func = 0; };

};

truct B {

struct Nested { virtual void B_Func = 0; };

};

truct MyClass : public A::Nested, public B::Nested {

void A_Func { cout << "A_Func called" << endl; } void B_Func { cout << "B_Func called" << endl; } };

void main {

MyClass m;  cout << "(A::Nested*)&m = " << (void*)(A::Nested*)&m << endl; cout << "(B::Nested*)&m = " << (void*)(B::Nested*)&m << endl; ((A::Nested*)&m)->A_Func; ((B::Nested*)&m)->B_Func;

} In this example, the compiler confuses (A::Nested*) and (B::Nested*), so the same values are printed for both ((A::Nested*)&m) and ((B::Nested*)&m) when they should be different. This also causes the call to B_Func on the last line to call A_Func instead.

Keywords: kbbug kbfix kbvc600fix KB143082

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