Linker errors with static abstract class...

[Shamino]

Hello, I'm trying to do this:

#include "stdafx.h"
#include "Menu_State.h"
#include "Play_State.h"
#include "IO.H"

void Menu_State::handle_events(State_Manager * state_manager)
{
	result = IO::instance().get_input();
	
	switch(result)
	{	
	case 1: // play blackjack
		state_manager->change_state(Play_State::Instance());
/*
		if(players.size() == 0)
		{
			initialize_players(2);
		}
		pot = new Pot;
		deck = new Deck;
		deck->shuffle_deck();
		players[0].draw(*(deck), 2);
		players[1].draw(*(deck), 1);
		return 3;
	case 2: // quit game
		return 4;
	default:// invalid entry
		std::cout << "Please enter 1 or 2.\n";
		return 0;
*/
	}
}

I've bolded the error producing line. It's a function that returns a static instance of the Play_State class, it is a singleton.

#ifndef PLAY_STATE_H
#define PLAY_STATE_H
#include "Gamestate.h"

class Play_State : public Gamestate
{
public:
	void init();
	void cleanup();

	void handle_events(State_Manager * state_manager);
	void update();
	void print();

	static Play_State * Instance() 
	{
		return &play_instance;
	}

protected:
	Play_State() {};
private:

	static Play_State play_instance; 
};
#endif

I've done something similar to this before and never got a linker error, although I've never done this with a derived class before...

Here is the Gamestate abstract class:

#ifndef GAMESTATE_H
#define GAMESTATE_H
#include "State_Manager.h"
class State_Manager;
class Gamestate
{
public:

	virtual void init() = 0;
	virtual void cleanup() = 0;

	virtual void update(State_Manager * state_manager) = 0;
	virtual void print(State_Manager * state_manager) = 0;
	virtual void handle_events(State_Manager * state_manager) = 0;

	void change_state(State_Manager * state_manager, Gamestate * state);

  protected: Gamestate() { }
};
#endif

I'm getting error messages when trying to grab an instance of the Play_State.

------ Build started: Project: Blackjack, Configuration: Debug Win32 ------
Compiling...
Menu_State.cpp
Generating Code...
Skipping... (no relevant changes detected)
Play_State.cpp
Linking...
Menu_State.obj : error LNK2001: unresolved external symbol "private: static class Play_State Play_State::play_instance" (?play_instance@Play_State@@0V1@A)
C:\Documents and Settings\jcoleman\Desktop\Blackjack\Debug\Blackjack.exe : fatal error LNK1120: 1 unresolved externals
Build log was saved at "file://c:\Documents and Settings\jcoleman\Desktop\Blackjack\Blackjack\Debug\BuildLog.htm"
Blackjack - 2 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

Any ideas as to why this is happening?

[Elysia]

Add
play_instance Play_State::Play_State;
To your class source file.
In case you haven't done so.

[Shamino]

Which class source file are you referring to?

play_instance is what Play_State::Instance() should return....

I can't initialize play_instance because it only exists privately in Play_State, Instance() should return play_instance...

[Elysia]

Wait, let's try that again.
Play_State Play_State::play_instance;
Add to Play_State class source file.

[Shamino]

Sorry if I seem inept, but I've never seen these sorts of link errors before:

------ Build started: Project: Blackjack, Configuration: Debug Win32 ------
Compiling...
Play_State.cpp
Linking...
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::init(void)" (?init@Play_State@@UAEXXZ)
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::cleanup(void)" (?cleanup@Play_State@@UAEXXZ)
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::update(class State_Manager *)" (?update@Play_State@@UAEXPAVState_Manager@@@Z)
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::print(class State_Manager *)" (?print@Play_State@@UAEXPAVState_Manager@@@Z)
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::handle_events(class State_Manager *)" (?handle_events@Play_State@@UAEXPAVState_Manager@@@Z)
C:\Documents and Settings\jcoleman\Desktop\Blackjack\Debug\Blackjack.exe : fatal error LNK1120: 5 unresolved externals
Build log was saved at "file://c:\Documents and Settings\jcoleman\Desktop\Blackjack\Blackjack\Debug\BuildLog.htm"
Blackjack - 6 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

That is what happens when I add that line of close to the Play_State source file...

What are you trying to accomplish with that line of code?

[Elysia]

Static members of a class must be defined within the source file or you'll get linking errors.
You can also try a rebuild. Technically, it should work.

[Shamino]

So are the 5 linker errors I currently have coming from my other gamestate classes not looking like the one we just changed? I've rebuilt the project and it still does not compile, I'm trying in VS2005 express.

[Elysia]

Dang.
A good question would be - why do you need a static variable of its own type in the class?
Now, another one for you: are you actually defining all those functions, init, handle_events is your Play_State source file?
Is there a
void Play_State::init()
there?

[cpjust]

I think the new errors you're getting are because you don't have those functions defined (only declared). Add function bodies for them in your .cpp file.

[Shamino]

I manage to acquire 5 more linker errors every time I do this to one of my gamestate classes, now I have this:

------ Build started: Project: Blackjack, Configuration: Debug Win32 ------
Compiling...
Menu_State.cpp
Linking...
Menu_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Menu_State::init(void)" (?init@Menu_State@@UAEXXZ)
Menu_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Menu_State::cleanup(void)" (?cleanup@Menu_State@@UAEXXZ)
Menu_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Menu_State::update(class State_Manager *)" (?update@Menu_State@@UAEXPAVState_Manager@@@Z)
Menu_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Menu_State::print(class State_Manager *)" (?print@Menu_State@@UAEXPAVState_Manager@@@Z)
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::init(void)" (?init@Play_State@@UAEXXZ)
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::cleanup(void)" (?cleanup@Play_State@@UAEXXZ)
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::update(class State_Manager *)" (?update@Play_State@@UAEXPAVState_Manager@@@Z)
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::print(class State_Manager *)" (?print@Play_State@@UAEXPAVState_Manager@@@Z)
Play_State.obj : error LNK2001: unresolved external symbol "public: virtual void __thiscall Play_State::handle_events(class State_Manager *)" (?handle_events@Play_State@@UAEXPAVState_Manager@@@Z)
C:\Documents and Settings\jcoleman\Desktop\Blackjack\Debug\Blackjack.exe : fatal error LNK1120: 9 unresolved externals
Build log was saved at "file://c:\Documents and Settings\jcoleman\Desktop\Blackjack\Blackjack\Debug\BuildLog.htm"
Blackjack - 10 error(s), 0 warning(s)
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

[Cactus_Hugger]

It looks like you only have the declarations for those functions... did you actually code the functions that the linker is complaining about? And are you certain they're being compiled/linked?

[Shamino]

I think the new errors you're getting are because you don't have those functions defined (only declared). Add function bodies for them in your .cpp file.

Good eye, let me see if I can clear up some errors this way..

[Elysia]

Actually, make life easier for us and show the source files you have now.

I think the new errors you're getting are because you don't have those functions defined (only declared). Add function bodies for them in your .cpp file.

I have a feeling it's that too

I believe you're confused about inheritance a little, Shamino?

[Shamino]

I guess this is what happens naturally when you dont complete your code bahaha

That solved the problem cpjust, thanks alot!

It was just a matter of not realizing the compiler would complain if I didn't add the implementations into the source files..
I thought it would automatically assume an empty function body :d

[Elysia]

Yeah well, you can see that the linker complains about missing symbols.
unresolved external symbol "public: virtual void __thiscall Menu_State::init(void)"
Pretty much reads: "Unable to find the function virtual void Menu_State::init()".
But yes, cpjust beat me to it by just a hair :/