C++ Using a reference function from header file in the cpp?

Question

I have a header file and a cpp file. In the .h file I declared a class and a function with returning a reference:

.h file :

#include <iostream>
class testclass {
    Car &createCar(int x, int y);
}

.cpp file :

#include<testclass.h>
Car testclass:&createCar(int x, int y)
{
  ....
}

But when I try to access the function in the .cpp file I get an error:

Declaration is not compatible

Answer 1

The function definition in .cpp file should be compatible with its decleration in .h file so modify it as follows.

.cpp file:

#include"testclass.h"
Car& testclass::createCar(int x, int y)
{
  ....
}

Note that I modified <testclass.h> to "testclass.h" . use the brackets only with the built in headers.

Follow the following line if you want to know why you should use "testclass.h" instead of <testclass.h> and which one of them you should use Link

Answer 2

In your .h file, & is not a reference to a function. The & is part of the function's return type. So, the function actually returns a reference to a Car instance. It would help you to understand it if you actually write it that way:

Car& createCar(int x, int y);

As such, in the .cpp file, you need to move the & to the return type to match the declaration:

#include <iostream>

class testclass {
    Car& createCar(int x, int y);
};

#include "testclass.h"

Car& testclass::createCar(int x, int y)
{
  ....
}