How can I create a polymorphic object on the stack?

Question

How do I allocate a polymorphic object on the stack? I\'m trying to do something similar to (trying to avoid heap allocation with new)?:

A* a = NULL;

switch         


        

Answer 1

A combination of a char array and placement new would work.

char buf[];
A *a = NULL;

switch (some_var)
{
case 1:
    a = new(buf) A;
    break;
case 2:
    a = new(buf) B;
    break;
default:
    a = new(buf) C;
    break;
}

// do stuff with a

a->~A(); // must call destructor explicitly