Aggregate has incomplete data type?

[Davitosan]

Following suggestions I received on this site, I've been trying to work with multiple files and applying OOP concepts. When trying to compile, the following warning appears:

Aggregate "App app" has incomplete data type and cannot be defined.

Here are the files:

Main.cpp

#include "nave_v2.h"

int main()
{
	App app;
	while (app.IsOpen())
	{
		app.Clear();
		app.Display();
		app.GetKey();
	}

	return 0;
}

main.h

#ifndef CLASSES
#define CLASSES

class App;

#endif 

classes.cpp

#include "SFML/Graphics.hpp"

class App
{
	sf::RenderWindow window;
	sf::Event keyPress;

	int SCREEN_WIDTH;
	int SCREEN_HEIGHT;
	int SCREEN_DEPTH;

	public:

		App()
		{
			SCREEN_WIDTH = 800;
			SCREEN_HEIGHT = 600;
			SCREEN_DEPTH = 32;
			window.Create(sf::VideoMode(SCREEN_WIDTH, SCREEN_HEIGHT, SCREEN_DEPTH), "Window");
		}

		void Display()
		{
			window.Display();
		}

		void Clear()
		{
			window.Clear();
		}

		bool IsOpen()
		{
			return window.IsOpened();
		}

		void ProcessKey()
		{
			switch (keyPress.Key.Code)
			{
				case sf::Key::Escape:
					window.Close();
					break;
				default:
					break;
			}
		}

		void GetKey()
		{
			window.GetEvent(keyPress);
			if (keyPress.Type == sf::Event::KeyPressed) ProcessKey();
		}

};

I'm not sure what incomplete data type means. Reading around, I thought it had something to do with the void functions, but when I changed them all to int and had them return 0, the compiler reported the same error.

If I use a single file, the program compiles OK.

Any replies will be appreciated.

[moorecm]

Class definitions go in header files. The compiler is saying that it doesn't know enough about App to let you create one.

It's seeing something like this:

class App; // forward declaration only (an incomplete type)

int main() {
    App app; // ERROR!
...

It needs to see:

class App { /* what an App is */ };

int main() {
    App app; // Oh yeah, an App.  No problem.
...

Remember that header files are just inserted verbatim by the preprocessor.

[Davitosan]

Thanks, it works now :D

But I thought that the point of header files was to link classes.cpp and main.cpp as if they were the same file...

I'll keep on reading. Thanks again!