Is this an error in "More Effective C++" in Item28?
- by particle128
I encountered a question when I was reading the item28 in More Effective C++ .In this item, the author shows to us that we can use member template in SmartPtr such that the SmartPtr<Cassette> can be converted to SmartPtr<MusicProduct>.
The following code is not the same as in the book,but has the same effect.
#include <iostream>
class Base{};
class Derived:public Base{};
template<typename T>
class smart{
public:
smart(T* ptr):ptr(ptr){}
template<typename U>
operator smart<U>()
{
return smart<U>(ptr);
}
~smart(){delete ptr;}
private:
T* ptr;
};
void test(const smart<Base>& ) {}
int main()
{
smart<Derived> sd(new Derived);
test(sd);
return 0;
}
It indeed can be compiled without compilation error. But when I ran the executable file, I got a core dump. I think that's because the member function of the conversion operator makes a temporary smart, which has a pointer to the same ptr in sd (its type is smart<Derived>). So the delete directive operates twice. What's more, after calling test, we can never use sd any more, since ptr in sd has already been delete.
Now my questions are :
Is my thought right? Or my code is not the same as the original code in the book?
If my thought is right, is there any method to do this?
Thanks very much for your help.
