virtual class & template error

[Blessman11]

hi

how is a class pure virtual class with a template inherited?


Pure virtual class

template<class xUsers_states>
class CStates
{

	CStates(void);
	
public:
		
	//BEGIN STATE:
	//take message from previus state 
	//to see if transisation is possible
	// return 1 for success, 0 for fail
    virtual FAST_BOOL Enter(xUsers_states*)=0;
	
	//EXECUTE OUR STATE:
	//Now lets get things rolling
	virtual void Execute(xUsers_states*)=0;
	
	//EXITING STATE:
	//Pass message to our successor
	//return our address to let the successor know, 
	//this message affects the call of action of our successor
	virtual CStates<xUsers_states>* Exit(xUsers_states*)=0;
	
	//virtual destructors are needed for pure virtual classes
	//its children will handle differently
	virtual ~CStates(void);
};

Here: my attempt to inherite it, the issue here is that it refuses to achknowledge my "CGAME_MANAGER" even though I've inherited it in the template through "public CStates<CGAME_MANAGER>".

Whats my mistake?

class CStart_Menu :
	public CStates<CGAME_MANAGER>
{
private:
	CStart_Menu(void);

public:
	//BEGIN STATE:
	//take message from previus state 
	//to see if transisation is possible
	// return 1 for success, 0 for fail
    virtual FAST_BOOL Enter(CStates*);
	
	//EXECUTE OUR STATE:
	//Now lets get things rolling
	virtual void Execute(CGAME_MANAGER*);
	
	//EXITING STATE:
	//Pass message to our successor
	//return our address to let the successor know, 
	//this message affects the call of action of our successor
	virtual CStates* Exit(CStates*);

	//SINGLETON DECLARATION
	static CStart_Menu * Instance();
	
	virtual ~CStart_Menu(void);
};

[Computergeek01]

"CGAME_MANAGER" does not define a type, so you need a template declaration for it above your definition of "CStart_Menu". I'm glad to see a user in the beginner forums using objects, good work so far.

[eypros]

I think you have the same problem as here:
http://www.cplusplus.com/forum/general/51699/

Basically you need to explicitly tell the compiler a member function of base class exists. See the other post for possible options

[Disch]

In the future, it would really help if you posted the actual errors rather than your interpretation of what the error means.

You have 2 problems here:

1) Your Enter and Exit functions take a xUsers_states* as a parameter in the parent class, but a CState* in the child class (note this is wrong for 2 reasons: one is that they don't match, and two is that CState isn't a class -- it's a template -- so you can't have a pointer to it.)

One solution here would be to change CStart_Menu so that Enter and Exit both take CGAME_MANAGER* as a parameter.



2) CState's ctor is private, so CStart_Menu won't be able to access it (so you won't be able to derive from it). One solution is to make it protected instead of private.

[Blessman11]

CStart_Menu was going to be a singleton thats why its private

[Computergeek01]

Protected is the same as Private except that derived classes can inherit it.

[Blessman11]

Here are the errors:

But I now think I'm at the age where posting just errors may seem like code dumping, so I been trying to explain them instead. but here are the errors anyway

1>------ Build started: Project: Game state machine, Configuration: Debug Win32 ------
1>Build started 10/10/2011 14:59:59.
1>InitializeBuildStatus:
1>  Touching "Debug\Game state machine.unsuccessfulbuild".
1>ClCompile:
1>  game_main.cpp
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(11): error C2065: 'CGAME_MANAGER' : undeclared identifier
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(12): error C2955: 'CStates' : use of class template requires template argument list
1>          g:\year2\game software engineering gameng\mazuma engine\game state machine\states.h(22) : see declaration of 'CStates'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(21): error C2061: syntax error : identifier 'CGAME_MANAGER'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(25): error C2061: syntax error : identifier 'CGAME_MANAGER'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(31): error C2061: syntax error : identifier 'CGAME_MANAGER'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(37): warning C4511: 'CStart_Menu' : copy constructor could not be generated
1>          g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(10) : see declaration of 'CStart_Menu'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(37): warning C4512: 'CStart_Menu' : assignment operator could not be generated
1>          g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(10) : see declaration of 'CStart_Menu'
1>  GAME_MANAGER.cpp
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(11): error C2065: 'CGAME_MANAGER' : undeclared identifier
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(12): error C2955: 'CStates' : use of class template requires template argument list
1>          g:\year2\game software engineering gameng\mazuma engine\game state machine\states.h(22) : see declaration of 'CStates'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(21): error C2061: syntax error : identifier 'CGAME_MANAGER'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(25): error C2061: syntax error : identifier 'CGAME_MANAGER'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(31): error C2061: syntax error : identifier 'CGAME_MANAGER'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(37): warning C4511: 'CStart_Menu' : copy constructor could not be generated
1>          g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(10) : see declaration of 'CStart_Menu'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(37): warning C4512: 'CStart_Menu' : assignment operator could not be generated
1>          g:\year2\game software engineering gameng\mazuma engine\game state machine\start_menu.h(10) : see declaration of 'CStart_Menu'
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\game_manager.cpp(9): error C2664: 'CStateMachine<qXType_state>::SetCurrentState' : cannot convert parameter 1 from 'CStart_Menu *' to 'CStates<xUsers_states> *'
1>          with
1>          [
1>              qXType_state=CGAME_MANAGER
1>          ]
1>          and
1>          [
1>              xUsers_states=CGAME_MANAGER
1>          ]
1>          Types pointed to are unrelated; conversion requires reinterpret_cast, C-style cast or function-style cast
1>  Start_Menu.cpp
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\statemachine.h(46): error C2664: 'CStateMachine<qXType_state>::State_Active' : cannot convert parameter 1 from 'CStates<xUsers_states> *' to 'CStates<xUsers_states> &'
1>          with
1>          [
1>              qXType_state=CGAME_MANAGER
1>          ]
1>          and
1>          [
1>              xUsers_states=CGAME_MANAGER
1>          ]
1>          and
1>          [
1>              xUsers_states=CGAME_MANAGER
1>          ]
1>          g:\year2\game software engineering gameng\mazuma engine\game state machine\statemachine.h(44) : while compiling class template member function 'unsigned char CStateMachine<qXType_state>::ChangingState(CStates<xUsers_states> *)'
1>          with
1>          [
1>              qXType_state=CGAME_MANAGER,
1>              xUsers_states=CGAME_MANAGER
1>          ]
1>          g:\year2\game software engineering gameng\mazuma engine\game state machine\game_manager.h(41) : see reference to class template instantiation 'CStateMachine<qXType_state>' being compiled
1>          with
1>          [
1>              qXType_state=CGAME_MANAGER
1>          ]
1>g:\year2\game software engineering gameng\mazuma engine\game state machine\statemachine.h(51): error C3867: 'CStates<xUsers_states>::Exit': function call missing argument list; use '&CStates<xUsers_states>::Exit' to create a pointer to member
1>          with
1>          [
1>              xUsers_states=CGAME_MANAGER
1>          ]
1>  Generating Code...
1>
1>Build FAILED.
1>
1>Time Elapsed 00:00:01.29
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

[Disch]

So yeah... in addition to the above 2 problems, CGAME_MANAGER isn't defined. You need to forward declare it:

class CGAME_MANAGER;

template<class xUsers_states>
class CStates
{
  //... 

You also have errors in unposted code....

error C2664: 'CStateMachine<qXType_state>::State_Active' : cannot convert parameter 1 from 'CStates<xUsers_states> *' to 'CStates<xUsers_states> & 

This one seems pretty self explanitory. You're passing a pointer to a function that takes a reference.

[Blessman11]

thanks Disch, those errors where fixed, but now I've got the using class issue:

basically, it seems to accept the declaration in the headerfile, but I can't redeclare these pure I cant redeclare them in the .cpp file or even tell them that I need them to be virtual.

extern class CGAME_MANAGER; 

class CStart_Menu :
	public CStates<CGAME_MANAGER>
{
private:
	CStart_Menu(void);

public:
	//BEGIN STATE:
	//take message from previus state 
	//to see if transisation is possible
	// return 1 for success, 0 for fail
	using CStates<CGAME_MANAGER>::Enter(CGAME_MANAGER*);


	//EXECUTE OUR STATE:
	//Now lets get things rolling
	using CStates<CGAME_MANAGER>::Execute(CGAME_MANAGER*);
	
	//EXITING STATE:
	//Pass message to our successor
	//return our address to let the successor know, 
	//this message affects the call of action of our successor
	using CStates<CGAME_MANAGER>::Exit(CGAME_MANAGER*);

	//SINGLETON DECLARATION
	static CStart_Menu * Instance();
	
	virtual ~CStart_Menu(void);
};

#define stSTART_MENU CStart_Menu::Instance() 

this section is the problem

//eturn 1 for success, 0 for fail
       using CStates<CGAME_MANAGER>::Enter(CGAME_MANAGER* qp_laststate)
	{
		//Test if there is a transisation
		//from the previous state
		qp_laststate->Use_StateMachine()->CurrentState();
		/* 
		if ((qp_laststate->Use_StateMachine()->CurrentState())== (extern)knownstate)
		if(!(execute trasition()))//returns true if transition complete
		{return 0}//else carry on with transition
		else if (try known transition number 2)
		.....
		
		
		
		else
		//ADD ANIMATION:

		*/
		//LISTEN FOR BUTTONS (skip option here)

		
		//transition complete
		return 1;
	}
	

[Disch]

I'm not sure I understand your question.

And why did you put extern and using everywhere? By putting those usings there, it's like you deleted the function prototypes.

Get rid of that riff-raff. You don't need it.

[Blessman11]

I meant to say how could I define the following virtual function in a .cpp file
using CStates<CGAME_MANAGER>::Exit(CGAME_MANAGER*);