C++ inheritance trouble

Question

Recently I have been making a game in C++ and I have ran into trouble when trying to use inheritance.

What I'm trying to do is create cars and a player which is also some form of a car. Both of those things require an x and y position, a method to get those and a render. Since I want the code to have a good quality, I wanted to only write that code once. I did part of that in the following Entity file: http://pastebin.com/nceanyQD

And the Entity header: http://pastebin.com/CLTv9B0Y

Then I have this in the Car header: http://pastebin.com/T9v0WGKd

And finally this in the Car file: http://pastebin.com/CJ5wnby5

When I run this code it will give several errors. First of all in the Player.h right under the Entity line telling me: Entity base class undifined.

Another error in a Game file (which renders and updates everything) in the following code:

Car Game::getCarAtLocation(int x, int y)
{
    vector<Car>::iterator iter = cars.begin();

    for(iter = cars.begin(); iter != cars.end(); ++iter)
    {
        if(iter->getX() == x)
        {
            if(iter->getY() == y)
            {
                return *iter;
            }
        }
    }
    return NULL;
}

It tells me getY and getX is not a member of Car. However, the same getY and getX do work totally fine in the operator<< overload in the Car file itself.

Finally the last error I'm getting in the Entity.h file is 'class' type redifinition.

What am I doing wrong and how do I fix it?

If there is any other code required, it can be downloaded here. https://dl.dropboxusercontent.com/u/59067404/BalCab.zip

Answer 1

Second error is simple - iterator must be "const", because getY() and getX() has const modifier.

vector<Car>::const_iterator iter = cars.begin();

In class Car in overload operator<< works because Car argument "const"

friend ostream& operator<<(ostream& os, const Car car);

And why in Car.cpp change signature of overloaded operator you write:

ostream& operator<<(ostream& os, Car car) ......

must be same as declaration

ostream& operator<<(ostream& os, const Car car)

Answer 2

Add include guards to your header files or put

#pragma once 

at the beginning of the headers

Entity.h file is 'class' type redifinition.

means that the compiler is presented with the the text

class Entity { [...] };

more than once.

You can think of an include statement as a copy-paste. Everything you write in

file.h

will be copy-pasted into any file that has the statement

#include "file.h"

when you call the compiler (press the build/make button in your IDE)

If your source file now has

#include "Car.h"
#include "Entity.h"

the definition the compiler will now have two copies of your Entity definition.