头文件问题的无限循环 [英] infinite loop of headerfile problem

问题描述

大家好
我面临一个问题.
假设我有两个class.class A和class B.
在A类中，我定义了B类的对象，在B类中，我定义了A类的对象.
当我尝试运行代码时，它显示出在classA之前放置分号的错误.
代码是这样的.

#include"B_wnd.h"
类A_wnd {
int xy;
B_wnd b_obj;
};







在B类声明中，我正在这样使用



#include"A_wnd.h"
B_wnd类{
int bx;
A_wnd a_obj;
};




当我尝试查看代码时，出现错误.
谁能帮助我摆脱这个问题.

Hi All
I am facing a problem.
let suppose i have two classes.class A and class B.
in class A i defines the object of class B,and in class B i defines the object for class A.
When i try to run the code it show the error that to place a semicolon before the classA .
the code is something like this .

#include"B_wnd.h"
class A_wnd{
int xy;
B_wnd b_obj;
};







in class B declaration i am using like this



#include"A_wnd.h"
class B_wnd{
int bx;
A_wnd a_obj;
};




when i try to ru the code ,i get the error.
can any one help me in getting rid off from this problem.

推荐答案

那是一个循环引用，您不能这样做.重构代码.

That''s a circular reference, and you can''t do that. Refactor your code.

#include"B_wnd.h"
class A_wnd{
int xy;
B_wnd b_obj;
};

#include"A_wnd.h"
class B_wnd{
int bx;
A_wnd a_obj;
};

首先，为什么需要循环参考?任何真正的需求还是您只想测试?

首先，标题将具有循环引用.您可以使用包含保护程序来解决该问题.大多数情况下，所有高级C/C ++处理器都可以避免这种情况，但是始终在包含标头时使用包含防护.那么在Microsoft VCC中，我认为您可以使用

First of all why do you need a circular reference? Any real need or you want just to test?

First of all the headers will have circular reference. You can use a include guard to over come that. Mostly all advanced C/C++ processors can avoid it, but always when you include headers use include guards. In Microsoft VCC then I think you can use

#pragma once

克服这个问题后，您会遇到第二个问题.

假设您创建了一个A_wnd类型的对象. 调用A_wnd的构造函数时，它将调用B_wnd的构造函数.在此内部，将再次调用A_wnd的构造函数.这是一个递归问题.您将出栈并且会崩溃.

您可以使用指针或引用来代替实际对象.

After you overcome this you have a second problem.

Suppose you create an object of type A_wnd.
When the constructor of A_wndis called it calls the constructors of B_wnd. Inside this again constructor of A_wnd will be called. This is a recursive problem. You will go out of stack and there will be crash.

You can use pointers or reference instead of real objects.

使用此:

//A_wnd.h
#ifndef A_H
#define A_H
#include "B_wnd.h"

class B_wnd;

class A_wnd
{
    public:
	B_wnd* m_b;
};

#endif

//B_wnd.h
#ifndef B_H
#define B_H

#include "A_wnd.h"
class A_wnd;

class B_wnd
{
	public:
	A_wnd* f;
};
#endif

2个重要问题:
1. ifndef-避免重新定义
2.转发定义(例如，类B_wnd).

2 important issues:
1. ifndef - to avoid redefinition
2. Forward definition (class B_wnd; for example).

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