error C2079: 'room::goldC' uses undefined class 'goldContainer' - visual-c++

Question

i'm trying to create a room which has a goldContainer
The goldContainer is defined in a separate .h file.
When i'm trying to compile it says
error C2079: 'room::goldC' uses undefined class 'goldContainer'
The class voor room:
#pragma once
#include <SFML\Graphics.hpp>
#include "screenSettings.h"
#include "floorplanPatch.h"
#include "floorplanPatchContainer.h"
#include "enemyContainer.h"
#include "goldContainer.h"
class goldContainer;
class room{
public:
room(int themenr, floorplanPatchContainer &f);
void draw(sf::RenderWindow &window);
int getStartPoint();
int getEndPoint();
void addFloorplanPatch(int x, int y, int type, floorplanPatch *patch);
bool isSolid(sf::Vector2f position);
void addEnemy();
static const int FLOOR_TEXTURE1 = 0;
static const int FLOOR_TEXTURE2 = 1;
static const int FLOOR_TEXTURE3 = 2;
static const int FLOOR_TEXTURE4 = 3;
static const int WALL = 4;
static const int OBSTACLE = 5;
static const int COSMETIC = 6;
int floorplan[xAs][yAs];
enemyContainer* getEnemyContainer();
void room::addEnemy(int health);
private:
enemyContainer ec;
int startPoint = 1 + rand() % (yAs - 2);
int endPoint = 1 + rand() % (yAs - 2);
sf::RectangleShape rectangle{ sf::Vector2f{ tileSizeX, tileSizeY } };
sf::Texture wall;
sf::Texture obstacle;
sf::Texture floor1;
sf::Texture floor2;
sf::Texture floor3;
sf::Texture floor4;
sf::Texture cosmetic;
void drawBackgroundTile(sf::RenderWindow &window, int i, int x, int y);
goldContainer goldC;
};
it has class goldContainer; on line 8 otherwise it generates error code 2146.
Could someone maybe explain how to solve this error and/or why this occurs.
#pragma once
#include "gold.h"
#include "sound.h"
#include "player.h"
class player;
class room;
class goldContainer{
public:
goldContainer();
~goldContainer();
void checkPickedUp(player &player);
void draw(sf::RenderWindow &window);
void addGold(int amount, sf::Vector2f position, sf::Vector2f size);
void clearAllGold();
private:
std::vector<gold* > goldDrops;
sound goldPickup{ "sounds\\goldPickup.wav" };
};
I think it might be a circular depedency trough:
^->goldContainer->player->roomContainer->room->|
|<-<-<-<-<-<-<-<-<-<-<-<-<-<-<-<-<-<-<-<-<-<-< v

Answer 1

Let me show you the problem domain:
class Moon;
class Sun
{
void Rotate(Moon);
};
Now, you implement Sun::Rotate, without giving any class declaration (not forward declaration):
void Sun::Rotate(Moon m) // Error C2027
{
}
What you can do:
Ensure that before Sun::Rotate gets into compilation phase, Moon is declared (i.e. known to compiler by now). You need not to implement any method of Moon, just declare.
Example:
class Moon;
class Sun
{
void Rotate(Moon);
};
// Let it come by now
class Moon
{
public:
void PleaseRotate();
};
// Moon is known
void Sun::Rotate(Moon m)
{
m.PleaseRotate(); // It need not to be implemented by now.
}
Note that Moon::PleaseRotate definition would be resolved by linker, and hence its implementation is not needed before Sun::Rotate.