Cross reference and circular dependency. Header including itself indirectly

Question

placeable.h

#include "selectable.h"

class placeable : selectable
{
..
};

selectable.h

#include "game.h"


class selectable
{
..
};

game.h

#include "placeable.h"

class game
{
...
class placeable* holding;
...
};

Basically placeable.h includes selectable.h which includes game.h which includes placeable.h again.

The only solution i can think of is placing the placeable* in a new header, making it static/global and then include this new header in game.h and selectable.h.

I'm sorry i dint include header guards in the upper code. I assumed it was obvious. Header guards does not help in this case because of the inheritance, same thing goes with forward declaring.

score 5 · Answer 1 · answered Dec 23 '11 at 19:34

Only include headers if you MUST

Use forward declaration in preference to including:

You only need to include the header for class X iff:

You have a member of the class 'X'
You derive from the class 'X'
You pass a parameter of class 'X' by value.

Otherwise a forward declaration will suffice.

//  -> Don't do this #include "placeable.h"
class     placeable;  // forward declare
                      // Fine if you are using a pointer.

class game
{
    ...
    class placeable* holding;
    ...
};

PS. Add header guards.

score 3 · Answer 2 · answered Dec 23 '11 at 19:30

3

This means you have not properly encapsulated the functionality of your design. It should be higher-level includes lower level, not same-level includes same-level. If game is the higher level then selectable should not include game.h.

answered Dec 23 '11 at 19:30

Steve C

647
3
6

score 2 · Answer 3 · answered Dec 23 '11 at 19:32

2

This is a solved problem. It's called header guards. Try this inside ALL of your header files:

#ifndef __NAMEOFTHEFILE_H__
#define __NAMEOFTHEFILE_H__
// nothing goes above the ifndef above

// everything in the file goes here

// nothing comes after the endif below
#endif

Also, you can do this (this is known as a forward reference):

// game.h

class placeable;

class game { ...
    placeable* p;
};

answered Dec 23 '11 at 19:32

jmucchiello

18,754
7
41
61

2

Header guards only prevent multiple inclusion, they don't protect you from circular designs. – Puppy Dec 23 '11 at 19:36
And did the info about forward references help? You need header guards. And you need forward references. – jmucchiello Dec 24 '11 at 03:49

score 0 · Answer 4 · edited May 23 '17 at 12:31

0

There are two problems:

Circular headers dependency. Solution - #ifndef ...
Allocating space for unknown type. Solution - class placeable;

See more here

edited May 23 '17 at 12:31

Community

1
1

answered Mar 30 '15 at 07:24

Andrey Burykin

700
11
23

score -1 · Answer 5 · answered Dec 23 '11 at 19:33

-1

Use header guards in each of your header files to avoid this problem. In general, your header files should like this:

#ifndef PLACEABLE_H
#define PLACEABLE_H

//
// Class definitions and function declarations
//

#endif

answered Dec 23 '11 at 19:33

shargors

2,147
1
15
21

Cross reference and circular dependency. Header including itself indirectly

5 Answers5