Question

I am working on my c++ assignment and I try to use polymorphism in my program. in my program i want to store the pointer of some objects in a pointer vector right after they are constructed:

entities.push_back(&Invader4());
entities.push_back(&Invader3());
entities.push_back(&Invader2());
entities.push_back(&Invader1());
entities.push_back(&Invader0());

class Invader inherit class Entity, but when I try to access the element in entities, an accesss violation occurs. do i have to declare another Invader type vector to store these objects first?

Answer 1

You’re taking the address of a temporary, which is illegal (undefined behavior to be exact). Just dynamically allocate the memory:

entities.push_back(new Invader4());
entities.push_back(new Invader3());
entities.push_back(new Invader2());
entities.push_back(new Invader1());
entities.push_back(new Invader0());

don’t forget to delete the memory in the vector when you’re done.

Also, take a look into smart pointers, might be more appropriate here.

Edit: by deleting, I mean

for (int i = 0 ; i < entities.size() ; i++ )
    delete entities[i];

when you’re done with the vector.