error: expected class-name before ‘{’ token

Really don't understand why I get the compile error. I put a big arrow on the line this error appeared on. I've tried rearranging the order of the includes and stuff like that, but even if that worked I wouldn't understand why.

Code:

---


----MAIN.cpp----------------
#include <G3D/G3DAll.h>
#include <GLG3D/GLG3D.h>

#include "App.h"
#include "Demo.h"


int main(int argc, char** argv)
{
        GAppSettings settings;
        settings.window.width = 800;
        settings.window.height = 600;

        App app(settings);
        app.setDebugMode(true);
        app.debugController.setActive(true);

        app.run();
        return 0;
}

-----DEMO.h-------------------

#ifndef Demo_H
#define Demo_H

#include <G3D/G3DAll.h>
#include <GLG3D/GLG3D.h>
#include "App.h"

class Demo : GApplet {                  <<<<-----------------------------Here's the ERROR 
 public:
  Demo(App* app) : app(app) {}
    void doGraphics();

 private:
    const App* app;
};

#endif


------APP.h------------------
#ifndef App_H
#define App_H

#include <G3D/G3DAll.h>
#include <GLG3D/GLG3D.h>
#include "Demo.h"

class App : public GApp {
 public:
  App(const GApp::Settings& settings): GApp(settings) {}
                void main();
};

#endif

-------APP.cpp---------------

#include "App.h"

void App::main()
{
        Demo(this).run();
}

------DEMO.CPP-------------

#include "Demo.h"

void Demo::doGraphics() {
  app->renderDevice->clear(true, true, true);
  app->renderDevice->setProjectionAndCameraMatrix(app->debugCamera);
  Draw::axes(Vector3(0,4,0),app->renderDevice);
}

---

Is GApplet defined in one of those header files?
You should also be explicit about what kind of inheritance you want (i.e. public, protected or private), otherwise people might just think you forgot to add the keyword...

Spelling perhaps?

I see 'App' and 'GApp', but no 'GApplet'

You're mixing spaces and tabs - bad. Use ONE and stick with it. I recommend tabs.
And come on - one space for indentation - that's kind of cheap, isn't it? Use AT LEAST 4 spaces if you're going for spaces.

You have a recursive include between app.h and demo.h. There's no reason for app.h to include demo.h.

yeah I thought recursive include or something like that so I've been messing around with the include statements... Nothing works though.

The line in question should be "class Demo : public GApplet {"

I just don't understand this error.

If you have referencing headers, then you must use a forward declaration, like

Code:

---

class GApplet;

---

...before the code that uses it. Then include the proper header file inside the .cpp file.
It's difficult to test this because many of the required classes are missing, so it won't compile properly.

Instead of including App.h in Demo.h, use a forward declaration:

Code:

---

class App;

---

I still don't see anything in App.h that references Demo.h's contents in any way.