error C2504: 'Entity': base class undefined

Question

After searching on nearly every page covering this error, I couldn't find a solution that matched my problem. When including the header file for the base class in the file of the derived class, I get the error: "error C2504: 'Entity': base class undefined". I have three classes, a parent class, derived class, and an inbetween class that both of the other classes need access to. I'm making an entity class for my enemies and other entities to inherit from, but even after including its header, I still get the error. I've tried forward declarations for the parent class and they don't seem to do anything to no avail. Before looking at my code, ignore common.h, player.h, skeleton.h, game.h, and resourcemanager.h. Without futher ado, here is my code:

(Entity.h)

#include "Common.h"
#include "Tile.h";

class Entity {
public:
    Tile *isSideColliding(bool isSolid, string&& type);
    Tile* isTopColliding(bool isSolid, string&& type);
    Tile* isBottomColliding(bool isSolid, string&& type);

    Sprite sprite;
    RectangleShape topHitbox, bottomHitbox;
};

(Slime.h)

#pragma once
#include "Common.h"
#include "Game.h"
#include "Entity.h"
#include "Tile.h"
#include "ResourceManager.h"

class Slime: public Entity {
public:
    static vector<Slime> slimeVector;
    Slime(float& x, float& y);
    static void draw();
    static void update();
private:
    static const Vector2f SPRITE_DIMENSIONS;
    char dir;
    //Sprite sprite;
    //RectangleShape topHitbox, bottomHitbox;
    /*Tile* isSideColliding(bool isSolid, string&& type);
    Tile* isTopColliding(bool isSolid, string&& type);
    Tile* isBottomColliding(bool isSolid, string&& type);*/
    static const float GRAVITY;
    static const Vector2f TERMINAL_VELOCITY;
    Vector2f position, velocity;
};

(Tile.h)

#pragma once
#include "Common.h"
#include "Player.h"
#include "Skeleton.h"
#include "ResourceManager.h"
#include "Chest.h"
#include "Slime.h"

class Slime;

class Player;

class Skeleton;

class Tile {
public:
    Sprite sprite;
    static void draw();
    static void createLevelPathing();
    static void setupBackground();
    static vector<Tile> tileVector;
    Vector2f spriteDimensions;
    bool isSolid;
    string type;
private:
    Tile(float& x, float& y, string&& type, bool isSolid);
    Tile(int& x, int& y, bool isSolid);
    static void initTiles(int& levelPosX, int& levelPosY, const Image& image);
    static Image getRoomTemplate(int& templateType);
    static const float POSITION_SCALAR, SCALE;
    static const int START_TILE, DOWN_TILE, UP_TILE, UP_AND_DOWN_TILE, DOOR_TILE;
};

My goal is to inherit from entity to slime. I'm fairly sure my file setup is good though. Could anyone please help explain why I'm getting the error of no base class defined? Also, I would appreciate critisism on my file including and how I could better structure it. Thanks!

Answer 1

As Jerry pointed out in the comment, it is circular include.

This normally implies that something can be improved in the design. For example, why does the Entity has to care about the colliding logic? Can it instead expose some functions for the Tile module to calculate colliding?

Come back to your question. I suggest to:

1. In Entity, forward declare the Tile class. Move the #include "tile.h" to the .cpp file. Do the same for Slime.
2. In Tile, remove the #include and forward declaration for Entity and Slime, it seems they're completely unused there.

Again, I still believe it is better to rethink the flow and the responsibility of classes, which one does what. From what I can remember, circular dependencies will likely bite us later.