game::baseEntity * playerPointer = new game::playerEntity();
game::playerEntity * player = playerPointer;

where playerEntity is a subclass of baseEntity.
What I want is two pointers to the same playerEntity, one as a baseEntity pointer and the other as a playerEntity pointer. The former will be used to put it in with the rest of the objects in the collision detection code, and the latter will be used to interact with the playerEntity directly.
The above code does not compile, saying "error: invalid conversion from 'game::baseEntity*' to 'game::playerEntity*'"
How would I do what I want?

Thanks in advance.

You have defined playerPointer as type baseEntity.

You can't go backwards like that without an explicit cast.

J-Gamer's suggestion isn't fitted to what you want to do. You'll have to cast every time you want to work with playerPointer.

Just keep your code as it was and take care of that cast right there.

Read his OP. He wants have a handle to playerPointer so he can interact with it directly for some reason.

Exactly. So I don't see why you would do it that way.

If you need a handle to a child class so that you can call explicitly defined methods in that class, then the type for the handle should be the type of the child, not the parent.

public Car : Vehicle { ... }

Car myCar = new Car(); //correct
Vehicle myCar = new Car(); //incorrect

It's worded backwards in the OP

You technically don't need to define a game::baseEntity * at all if you're just storing it in a container next. You could just store it.

std::vector<game::baseEntity *> objects;

game::playerEntity * player = new game::playerEntity();

objects.push_back(player);

You may want to still create the base pointer first if you do anything else with it as a base before storing it.

I don't know what you're talking about.^[1]