Question

I’m very new to C++ and I have a problem passing a vector of pointers to objects. Specifically the problem is the objects are a subclass of the class the method is in. I’m getting an error:

'Player' was not declared in this scope

Player is a subclass of Visual and in my file Visual.cpp I have the following function which is also declared in my header file.

bool Visual::DrawStatusInformation(Timer* timer, std::vector<Player*>* playerList) {
    // Draw Info
}

I have tried forward declaring class Player; in my header file but I get the error:

error: invalid use of incomplete type ‘struct Player’
error: forward declaration of ‘struct Player’

I think the problem is that my definitions are circular, Player extends Visual but Visual must know about Player in order to be able to deal with a vector of Player pointers.

My question is:

If it is possible, how can I use a subclass in a parameter of a superclass method?

Answer 1

Player extends Visual but Visual must know about Player in order to be able to deal with a vector of Player pointers.

By files:

• Player.h – include Visual.h & move implementations to implementation file
• Player.cpp – should be OK
• Visual.h – forward declare Player
• Visual.cpp – include Player.h

This just fixes the compilation error, but your design also seems faulty. If Player is derived from Visual, why does the method

Visual::DrawStatusInformation(Timer* timer, std::vector<Player*>* playerList)

exist? I’m sure you can replace it with

Visual::DrawStatusInformation(Timer* timer, std::vector<Visual*>* playerList)

and override it in Player. Also, why a vector* and not a vector&?