Two classes in C ++ reference each other solutions

Reprinted from --- "https://blog.csdn.net/xiqingnian/article/details/41214539

I. Description of the problem

There are two classes A and B need to be defined, when the need to use the definition of A B, B when the need to use the definition of A.

Second, analysis

A and B both define and call in a document is certainly not possible, this will cause an infinite loop cycle two calls.

The fundamental reason is: A definition of the time, there are A B, so we need to see the B accounts for space, but also found time to see the need to know the A accounts for space, resulting in an endless loop.

Solution:

(1) Write two headers Ah and Bh are used to declare classes A and B;

(2) Write .cpp files are used to define the two classes A and B;

(3) into the header in the header file B in A;

(4) A file header is not introduced in the header file B, but using extern manner declaring class A, and, B is used when A is in the form of pointers to use.

Principle: In pointer with B calls A, B then A needs to know the size of the space and they will go to find the definition file B, although the definition file B and A did not import the header file, do not know the A accounts space, but due to time in B calls a pointer form with a, B only know the pointer 4 bytes can be, do not need to know the size of the space a really, that is, a B also know the size of the space of.

I understand - "One must have a pointer through a pointer (4 bytes) + extern declaration of way, to ensure that, when compiled Bh, and through; so at compile time Ah, directly by the

Three, C ++ examples

A header file of Ah:

#ifndef _A
#define _A
<strong>     # the include "of Bh" // A header file into a header file B </ strong>
//extern class B;

class A
{
private:
int a;
B objectB; header file // A head import file B, B when the call can not pointer

public:
A();
you geta () ;
void handle();
};

#endif _A

B header files Bh:

#ifndef _B
#define _B

<strong> // # the include "Ah" B // A header file does not import header files, you need to have three things to note!
extern class A ; // NOTE 1: extern statement needed A </ strong>

class B
{
private :
int b;
* ObjectA A; // Note 2: A call when the need to use a pointer
public :
B();
int getb () ;
void handle();
};

# Endif _B

A definition file of A.cpp:

#include <iostream>
<strong> #include "A.h"</strong>

using namespace std;

A::A()
{
this->a= 100;
}

int A::geta()
{
return a;
}

void A::handle()
{
cout<< "in A , objectb.b="<<objectb.getb()<< endl;
}

B's definition file B.cpp:

#include <iostream>
<strong> #include "B.h"
# The include "Ah" // NOTE 3: A is introduced inside B.cpp headers </ strong>

using namespace std;

B::B()
{
this->b= 200;
}

int B::getb()
{
return b;
}

void B::handle()
{
objects = new A ();
cout<< "in B , objecta->a="<<objecta->geta()<< endl;
}

main.cpp:

#include <iostream>
#include <cstdlib>
<strong> #include "A.h"
// # include "Bh" // because Ah which already contains Bh, so this does not need to import the Bh. </ Strong>

using namespace std;

void main ()
{
A a;
a.handle();
B b;
b.handle();

system( "pause");
}