So, there I am, sweating and trembling, looking at my IDE screen trying to understand why a nice delete instruction was crashing my program. It was very dark: I was calling delete upon a pointer to a base interface, hoping that it would destroy the derived class.
When that didn't happened and windows informed me that there was an error in MY PROGRAM, I couln't believe it. I started blaming windows, Microsoft and I almost committed the sacrilege of cursing Visual Studio. I expected that, if the correct destructor (the derived class' destructor) wasn't called, at least nothing would be done, since the derived class ( I'll present the classes shortly) had no real data, only two pointers to object. That didn't happen. C++ was trying to do something that he shouldn't, I can't even imagine what.
So I inserted a fake destructor in my base class, a virtual one, to make sure the right one was called. That's when things got confused in my mind: my compiler wouldn't let me make a pure virtual destructor, which meant that interfaces don't have destructors. But if that is true, when I kill an interface, why doesn't the right destructor is called?
Of course, I have a clue... the derived class is a template, and maybe that is interfering with the dynamic binding.
For demonstrative purposes only, here are simulacrums of my classes:
[source=C++]
class Interface
{
void SomeMethod();
//virutal ~Interface(){} // uncomment this!
};
template<class T>
class Implementation : public virtual Interface
{
typedef (void)(T::*pFun0Void)();
typedef (void)(T::*pFun1Void)(void*);
Implementation(T* obj, pFun0Void func)
{
object = obj;
funcPointer = func;
}
~Implementation()
{
object = NULL;
funcPointer = NULL;
}
union
{
pFun0Void a;
pFun1Void b;
} funcPointer;
T* object;
};
int main()
{
Interface* test
= Implementation<SomeClass>(new SomeClass, SomeClass::someMethod);
delete test; // Bug if the virtual destructor in Interface is commented.
return 0;
}
What makes me crazy, is that, although the solution was obvious, Interfaces shouldn't have destructors, so we can't properly delete a Interface?
[Edited by - HeavyStorm on March 16, 2006 1:01:33 PM]
