C++ 循环头包括

2022-01-11 00:00:00 circular-dependency header c++ header-files

我知道之前有人问过与此类似的问题，但经过研究后，我仍然对循环标题包含有疑问.

I know that similar questions to this have been asked before but after doing my research I still have questions about circular header includes.

//FooA.h
#ifndef H_FOOA
#define H_FOOA

#include "foob.h"

class FooA{
   public:
      FooB *fooB;
};


//FooB.h
#ifndef H_FOOB
#define H_FOOB

class FooA;
class FooB{
   public:
      FooA *fooA;
};

现在，如果我有两个循环依赖项，这就是我在 stackoverflow 上看到人们解决问题的方式.我唯一的问题是，在我的 main.cpp 中，我必须先包含 fooa.h，然后再包含 foob.h

Now if I have two circular dependencies this is the way that I have seen people on stackoverflow get around the problem. My only problem with this is that in my main.cpp I must include fooa.h first and then foob.h

//main.cpp the right way
#include "fooa.h"
#include "foob.h"

//main.cpp that will surely get a compile error
#include "foob.h"
#include "fooa.h"

现在我的问题是有没有一种方法可以转发声明这些类，让我不必关心在 main.cpp 中包含头文件的顺序?"

Now my question is "Is there a way to forward declare these classes in a way that will allow me to not care about the order in which I include the header files in my main.cpp?"

推荐答案

有没有一种方法可以转发声明这些类，让我不必关心在 main.cpp 中包含头文件的顺序?

Is there a way to forward declare these classes in a way that will allow me to not care about the order in which I include the header files in my main.cpp?

由于您只处理简单的指针，因此您可以在这两种情况下使用前向声明:

since you are dealing with simple pointers only, you can use a forward declaration here in both cases:

FooA.h

#ifndef H_FOOA
#define H_FOOA

// #include "foob.h" << not needed!
class FooB;       // << substitute with a forward declaration of FooB

class FooA{
   public:
      FooB *fooB;
};
#endif

FooB.h

#ifndef H_FOOB
#define H_FOOB

class FooA;
class FooB{
   public:
      FooA *fooA;
};
#endif

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