CODEWITHSUNDEEP
c++staticlinker-errors
PSilo
PSilo

Reputation: 39

Static pointer to class linker error

I've been busting my head for some time now trying to figure out a solution. I want to inherit from a class with a static pointer but I geterror LNK2001: unresolved external symbol "protected: static class cGame * cEvent::mGame" (?mGame@cEvent@@1PAVcGame@@A)

Optimaly I would just initialize my class cEvent once and then dont pass pointers in the inherited classes.

#ifndef EVENT_H
#define EVENT_H

#include "game.h"


class cEvent
{
protected:
    static cGame* mGame;
public:
    cEvent(){;}
    virtual void doEvent(){;}
};

class cEventExitButton: public cEvent
{
private:
public:
    cEventExitButton(cGame *g){mGame = g;}
    void doEvent(){mGame->getWindow()->close();}
};

#endif

Upvotes: 1

Views: 2906

Answers (3)

JaredC
JaredC

Reputation: 5310

You have only declared mGame in the header file:

static cGame* mGame;

This tells the compiler that mGame exists and what its type is, but doesn't actually create space for mGame to exist. For this, you need to define it in a cpp file:

cGame* cEvent::mGame = [some intial value];

Now the linker has a location for mGame and anyone referencing it can point to that location. The linker can't do this with the header since multiple files may include the header. We only want a single location for mGame though, so it needs to go in a cpp file.

Upvotes: 1

NPE
NPE

Reputation: 500873

You have to define mGame in a .cpp file:

cGame* cEvent::mGame = ...;

(replace the ... as appropriate.)

Upvotes: 0

Sarfaraz Nawaz
Sarfaraz Nawaz

Reputation: 361702

You need to define the static member outside the class:

##include "game.h"

//do this .cpp file

cGame* cEvent::mGame = nullptr;

//or initialize it as : cGame* cEvent::mGame = create object!

Note that the static member in the class is only declaration, that is not definition.

Upvotes: 5

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