Header files, one can't work without the other & vice versa

[JS Lemming]

Welp, fell on my face. This one is kinda hard to explain.

I have stage class and I have various stage object classes (like hector and pipes). I need to pass an instance of stage to these stage objects but it requires that stage.h be included in these stage objects header files BUT stage.h needs to include these stage object headers in order to declare lists of them.

stage.h

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#include "gyroPipe.h"

using namespace std;

class stage
{
	public:
		list<gyroPipe*> gyroPipes;
		list<gyroPipe*>::iterator iGyroPipes;
...

gyroPipe.h

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#include "stage.h"

class gyroPipe
{
	public:
		gyroPipe(stage *stageInstance, int argColor, bool argVertical, int argX, int argY, int argLength);
...

I thought maybe extern could help me out here but I'm not sure how that would work.

[MarauderIIC]

Define a class prototype.

IE:

gyropipe.h

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#ifndef GYROPIPE_H //Standard include guards
#define GYROPIPE_H

//Only #include stage.h if you really need to
class Stage; //class prototype

class GyroPipe {
 GyroPipe(Stage* stageInstance...)
};
#endif

stage.h

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#ifndef STAGE_H
#define STAGE_H

//Only #include "gyropipe.h" if you really need to
class GyroPipe; //class prototype

class Stage {
 ....
};
#endif

Also, in C++, classes usually start with capital letters, as above. That way you can do Stage* stage, for instance

[Ginto8]

From your post, can't see anything wrong, except add a few things to prevent ambiguity:

at the beginning of the header files, put:

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#ifndef [filename]_H
#define [filename]_H

where [filename] is the filename without ".h" (in caps). This makes sure that the content only appears once.

At the end of the files, put:

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#endif

Lazyfoo does a better job at explaining it, here.

[MarauderIIC]

We must've posted at the same time :) Include guards prevent a file from being pasted into your project more than once by the compiler (causing compilation errors)

[Ginto8]

#defines have 2 purposes: creating constants and preventing ambiguity. You have now learned one of them. From two people at once.

[MarauderIIC]

C++ prefers const for the "creating constants," though =)

[Ginto8]

That's true, but there's no saying you can't use #define... I wasn't saying #define was the only way to do so, or even the best. It's just that those are really the only two reasons to use them these days, seeing as macros aren't as good as inline functions

[JS Lemming]

Thanks Mar, that's exactly what I needed.

FYI, my real code does have the guards. I just didn't post them so as to direct focus on the problem. I realize that was retarded of me.

[MarauderIIC]

Haha, np. With any luck someone that doesn't know about include guards will come across the post :)

[Ginto8]

Well, if you have the guards, there shouldn't be any problem. You might not understand how the compiler manages to make it work, but the compiler does.

[JS Lemming]

Well, if you have the guards, there shouldn't be any problem. You might not understand how the compiler manages to make it work, but the compiler does.

.... no. It doesn't. The way I had it didn't work. The files relied on each other in an impossible kind of way. Class prototyping fixed that.

[Falco Girgis]

Yeah, his problem wasn't that his classes were being redefined. They weren't being defined.

[MarauderIIC]

The pattern

Class A { B b};
Class B { A a};

is what you need a class prototype to solve. This was his issue.

[Ginto8]

Okay... yeah this is one of the reasons why I'm still in the learning process. I'm glad that I was wrong, actually. I learned something here.