Container covariance in C++

Question

I know that C++ doesn\'t support covariance for containers elements, as in Java or C#. So the following code probably is undefined behavior:

#include 

        

Answer 1

The general problem with covariance in containers is the following:

Let's say your cast would work and be legal (it isn't but let's assume it is for the following example):

#include 
struct A {};
struct B : A { public: int Method(int x, int z); };
struct C : A { public: bool Method(char y); };
std::vector test;
std::vector* foo = reinterpret_cast*>(&test);
foo->push_back(new C);
test[0]->Method(7, 99); // What should happen here???

So you have also reinterpret-casted a C* to a B*...

Actually I don't know how .NET and Java manage this (I think they throw an exception when trying to insert a C).