Question

I love declaring variables on the stack, especially when using the standard container. Each time you avoid a new, you avoid a potential memory leak.

I also like using polymorphism, ie class hierarchies with virtual functions. However, it seems these features are a bit incompatible: you can’t do:

std::vector<BaseType> vec;
vec.push_back(DerivedType())

or at least it seems you would lose the polymorphic nature of the object you push in.

So, is there any way to reconcile stack-based memory management and the use of virtual functions?

Answer 1

Well the obvious answer:

std::vector<BaseType*> vec;
DerivedType d;
vec.push_back(&d);

But probably not what you intended. d and vec better die at the same time; if vec outlives d you’ve got a bad pointer.

I think what you really want is something like Boost pointer containers:

boost::ptr_vector<BaseType> vec;
vec.push_back(new DerivedType());

So you don’t have to worry about leaks. The pointer containers were made specifically for the task of easing use and storage of polymorphic objects.