6 replies to this topic

[sacredheart]

Hi there,
I am trying to tackle a (probably fundamentally easy :) problem.

How do I fetch data from one function in class1 to another in class2?

I have my declarations.h file in which I declare my stuff:

class Player {

private:

	int PosY;

	int PosX;


public:

	Player() {

		PosY = 8;

		PosX = 13;

	};


	int GetCoords(int i);

	Player* player;


};


class DrawMap {

private:


public:

	DrawMap() {

	};

	

	int showMap();

	DrawMap* myMap;


};

In my functions.cpp file I include the declarations.h file, and define my class functions:

#include "declarations.h"


int Player::GetCoords(int i) {

	if(i == 1) {

		return PosX;

	} else {

		return PosY;

	}

}


int DrawMap::showMap() {

	int PosX = player->GetCoords(1); <-- This is wrong, but why and how?

	return 0;

}

The compiler says

error: ‘player’ was not declared in this scope

which I totally understand. DrawMap:: doesn't know what player is. But how do I get it to know that? Shouldn't Player* player be public and accessible?

TIA,
A

[WingedPanther]

DrawMap doesn't have any data about player, either as a method or class variable, so from player's perspective, it simply doesn't exist. Similarly, Player* player means each INSTANCE of Player has a pointer to a Player, but that doesn't mean you've created any instances of Player yet.

[dargueta]

Edit: I swear WP's answer wasn't there when I started writing. :D

That would be because you haven't declared a Player object named player in showMap nor DrawMap. It's kinda like declaring a variable X in one function and expecting another function to be able to access it. Unless it's public and static, or if you pass a pointer/reference to DrawMap, you won't be able to access it.

[sacredheart]

Thanks for the swift reply!

I forgot to mention, I do have

Player player(10.0, 10);

in main() -- which creates the player object (doesn't it?).

Should I create the object somewhere else than in main()?

BR,
A

[Alexander]

Could you show us your full code for the file of which contains main?

[WingedPanther]

Unfortunately, DrawMap doesn't know about variables you instantiate in main() unless they are passed to its methods as parameters.

[Zer033]

You could have the drawmap class construct with a player variable being passed to it to fill an internal player object it has, or make a method that receives a player object and stores info of it in an internal player object, or make showmap take a player object argument and work with it there, or you could declare the player you plan to work on as public static and access it even when an object isn't created using the scope resolution operator

 :: 

, if done like that each instance of Player will share that "working" player variable. You don't really need pointers to your classes within those classes you can call their functions within that class without them. Also if you're going to be passing parameters of objects by value or returning class objects or constructing using another class and those classes have pointer data members then you should create your own copy constructors so there won't be shallow copy and create destructors.