class has no constructor forward declaration - c++

Question

I'm trying to create a state engine in my game for the different screens. id start screen, maybe a file chooser in the future, overworld map, menu screen, etc. But when I forward declare the class it says there are no constructors.
GameState.h:
#pragma once
class GameState
{
public:
virtual ~GameState() {}
virtual void Update() {}
virtual void HandleEvents() {}
virtual void Draw(Graphics& gfx) {}
GameState* getCurrentState()
{
return currentState;
}
void ChangeState(GameState* state)
{
currentState = state;
}
protected:
SDL_Renderer* renderer;
GameState* currentState;
};
GameStates.h
#pragma once
#include "GameState.h"
#include "Texture.h"
#include "Keyboard.h"
class TitleGameState;
class IntroGameState : public GameState
{
public:
IntroGameState(SDL_Renderer* renderer, KeyboardClient& kbd)
:
kbd(kbd)
{
background = new Texture("red.png", renderer);
this->renderer = renderer;
}
~IntroGameState() {}
void HandleEvents()
{
while (!kbd.KeyEmpty())
{
KeyEvent e = kbd.ReadKey();
switch (e.GetCode())
{
case SDLK_RETURN:
if (e.IsPress())
{
currentState = new TitleGameState(renderer, kbd);
}
break;
}
}
}
void Logic() {}
void Draw(Graphics& gfx)
{
background->Draw(0, 0, gfx);
}
private:
Texture* background;
KeyboardClient& kbd;
};
class TitleGameState : public GameState
{
public:
TitleGameState(SDL_Renderer* renderer, KeyboardClient& kbd)
:
kbd(kbd)
{
background = new Texture("blue.png", renderer);
}
~TitleGameState() {}
void HandleEvents()
{
while (!kbd.KeyEmpty())
{
KeyEvent e = kbd.ReadKey();
switch (e.GetCode())
{
case SDLK_RETURN:
if (e.IsPress())
{
printf("OK");
}
break;
}
}
}
void Logic() {}
void Draw(Graphics&gfx)
{
background->Draw(0, 0, gfx);
}
private:
Texture* background;
KeyboardClient& kbd;
};
I define the class right afterwards, and I know I can just move it above IntroGameState, however when I implement the menu game state, it will go back and forth between the menu state and the overworld state. How can I get around this?
Compiler Error:
error C2514: 'TitleGameState' : class has no constructors
File: gamestates.h
Line: 28
Line 28 is this line of code:
currentState = new TitleGameState(renderer, kbd);

Answer 1

The error on the line currentState = new TitleGameState(renderer, kbd); is because the compiler has yet to see the constructor for the class. It doesn't know how to compile this code.
If you forward declare the class class TitleGameState; all you can declare is pretty much a pointer TitleGameState*.
To compile the code you have, you need to define the class before using. Note: defining the class does not mean defining all the methods as well. A class definition consists of the method and member declarations.
class TitleGameState : public GameState
{
public:
TitleGameState(SDL_Renderer*, KeyboardClient&);
~TitleGameState();
void HandleEvents();
// ...
};
class IntroGameState : public GameState
{
// ...
}
After the definition of the classes, you can then define the member functions;
/*inline*/ void TitleGameState::HandleEvents()
// inline is needed if the method is defined in a header file
// to help avoid linker errors
{
// ...
}