Multiple inclusion in multiple files

问题

I am making a small game.

In BattleRecord.h:

#ifndef _CHARACTER_H_
#define _CHARACTER_H_
#include "Character.h"
#endif

class BattleRecord
{
public:
    Character Attacker;
    Character Defender;
    Status status;
    int DamageDealt;    
    int GoldEarned;
    int ExpGained;
};

In Character.h:

#ifndef _EQUIPMENT_H_
#define _EQUIPMENT_H_
#include "Equipment.h"
#endif

class BattleRecord;
class Character
{
BattleRecord AttackEnemy(Character &Enemy);
}

In BattleRecord.h:

#ifndef _CHARACTER_H_
#define _CHARACTEr_H_
#include "Character.h"
#endif

#ifndef _BATLE_RECORD_H_
#define _BATLE_RECORD_H_
#include "BattleRecord.h"
#endif

class GUI
{
public:
//GUI Methods, and two of these:
void ViewStats(Character &Player);
void Report(BattleRecord Record)
}

The problem here is, my Character.h and BattleRecord.h need to include each other, and this definitely will cause multiple redefinition problem. Therefore, I used forward declaration in Character.h by adding:

class BattleRecord;

The problem is sovled. But then, the GUI.h needs BattleRecord.h again for reporting the battle, so I have to include BattleRecord.h into the GUI.h. I also have to include the Character.h in order to pass into the ViewStat function. I got error and stuck with this up to this piont.

回答1:

You're using inclusion guards wrong. They should appear in the file that you intend to prevent multiple inclusions only, and they should cover the entire file. (not just the includes).

For example, in BattleRecord.h

#ifndef _BATTLE_H_
#define _BATTLE_H_
#include "Character.h"

class BattleRecord
{
public:
    Character Attacker;
    Character Defender;
    Status status;
    int DamageDealt;    
    int GoldEarned;
     int ExpGained;
};

#endif // _BATTLE_H_

回答2:

Put your #endif at the end of the file not the end of your includes or use #pragma once at the top if your compiler supports this although that is less portable.

Edit:

To further explain what #ifdef & ifndef does is tell the compiler to include or exclude code entirely from compilation.

// if _UNQIUEHEADERNAME_H_ is NOT defined include and compile this code up to #endif
#ifndef _UNQIUEHEADERNAME_H_
// preprocessor define so next time we include this file it is defined and we skip it
#define _UNQIUEHEADERNAME_H_
// put all the code classes and what not that should only be included once here
#endif // close the statement

The reason you want to do this is because including a header file is basically saying "put all the code in this file here" if you did that multiple times then you'd have naming conflicts from redefining objects and slow compile times in the best scenario.

回答3:

In general, use forward declaration instead of includes. This minimizes how many includes you include file contains. The only exception is when the class you are defining is a derived class, then you need to include the base class.

回答4:

In addition to the include guard issues mentioned above (you also have a _CHARACTEr_H_/_CHARACTER_H_ mismatch that might cause you trouble on line 2 of GUI.h), you may want to revise your object design so that the Character does not AttackEnemy(), but rather there is a Battle() class where two Characters are referenced and a BattleRecord is produced after the battle. This would prevent the Character class from ever having to know about BattleRecords in the first place, would allow for the possibility of multi-Character battles in the future, having multi-turn battles, or having special battles through inheritance of the Battle class.

回答5:

OK everyone,

Thanks for helping me. I have rewritten all the inclusions for the header files as suggested, and it works flawless now. Take quite time a bit of time since I did it wrong for many classes.

来源：https://stackoverflow.com/questions/5106650/multiple-inclusion-in-multiple-files

标签

c++

header

c-preprocessor

include-guards