classes in c++

[cassius]

I am trying to learn classes in c++ and have a few questions..Does each class need its own header file or can I put several class definitions in one header.

 

What scope does a class have? is it global or not.

 

If I need a separate header file for each class where do I put my gameplay code ?

Hope this is clear and someone can clarity the problem.

[Rick]

You can put multiple class definitions in a file but it's very common practice to use 1 header/source file per class. I would stick with that if I were you.

 

A class doesn't really have scope because it's a blueprint of a type. When you create an object of a given class the scoping of that object follows the same rules as any other variable, which means you can make the variable global if you want (I would avoid this however).

 

Look at a C++ project in Leadwerks 3. Notice how it has an App class which an object of the App class gets created in int main() inside Main.cpp. The scope of that app object created from the App class is local to the int main() function. Then we call app->Start() to init some stuff then app->Loop()? (Update maybe? can't remember the name), and this is where the game runs. Now as far as structuring your game with classes this is a really big topic in which people have strong opinions about based on efficiency and maintainability of the project.

 

Normally you will want to put your class declarations in the header file like:

 

class Foo
{
private:
int i;
public:
void Update();
};

 

Then in the source file of the same name as the header file just different extension

 

void Foo::Update()
{
// actually do something
}

 

 

So classes just group variables and functions into a common object. Think of real world objects like a stapler. It has variables like color, size, paperClip count. It has functions like Staple(), Reload(), etc. You can represent this in plain C but nothing really links them together in C. In C++ the class is a way to link the variables and classes together in a way that makes sense.

 

 

In a LE3 C++ project in main.cpp.

 

App* app = new App;        // create a variable of the App blueprint

if (app->Start())                // call this classes Start function
{
  while (app->Loop()) {} // call this classes Loop() function
  delete app;                  // delete the app variable
}

[cassius]

Thanks rick that thrown more light on the subject. Looks like I have to undo a lot of stuff in my game in order to implement classes but in the long run it will be worth it.

[nate066]

Thanks rick that thrown more light on the subject. Looks like I have to undo a lot of stuff in my game in order to implement classes but in the long run it will be worth it.

If you still need help with c++ classes check out these tutorials. There all in a playlist, this specific tutorial talks about putting classes in separate files.

[Rick]

Following tutorials is a good idea. The first thing that stands out is the #ifndef stuff at the top. I think that's pretty old school these says where you can just use #pragma once instead, which is cleaner and I think most all modern compilers support it.

[cassius]

thanks nate066. Very usefull.

[xtreampb]

but i think people should be aware of the #ifndef because it help teaches preprocessor logic and methods. Not too much different but helps ease the exposure.

[cassius]

I learned the basic syntax of c\ c++ fairly quicklt. Its scope and visibility between files that has always given me a problem.

[Tim Shea]

Another thing to keep in mind is that if you plan on reusing elements of game code across multiple games, wrapping your classes in a namespace is a very good idea. Namespaces keep your class names from polluting the global context.