递归定义 [英] recursive definition in CPP

问题描述

我遇到这样的问题： UPDATE

class A
{
public:
    A(){}
    int i;
    B b;
};

class B
{
public:
    B(){}
    int j;
    A a;
};

当我在一个.h文件中定义它时，会给出一个错误。我认为问题是递归定义。但是有人可以帮我解决这个问题吗？

When I define it in one .h file, it would give an error. I think the problem is the recursive definition. But could someone help me how to solve such issue?

1. 错误C2146： ;'before identifier'b'c：\users\xingyo\documents\visual studio 2010\projects\cppalgo\recudef\test1.h 9 1 RecuDef

错误C4430：缺少类型说明符 - int。注意：C ++不支持default-int c：\users\xingyo\documents\visual studio 2010 \projects\cppalgo\recudef\test1.h 9 1 RecuDef

错误C4430：缺少类型说明符 - int。注意：C ++不支持default-int c：\users\xingyo\documents\visual studio 2010 \projects\cppalgo\recudef\test1.h 9 1 RecuDef

推荐答案

这在C ++中不可能逐字。解释是编译器需要完整的，而不仅仅是转发，一个类的声明，以便能够使用它作为另一个类的成员。它只需要一个类对象的大小。

This is not possible verbatim in C++. The explanation is that the compiler needs full, not just forward, declaration of a class to be able to use it as a member of another class. It simply needs the size of a class object.

C ++中的解决方法是使用或引用作为其中一个类的成员。这样你可以使用如下的前向声明：

The workaround in C++ (and in C) is to use a pointer or a reference as a member of one of the classes. That way you can use forward declaration as follows:

class A; // forward declaration

class B {
    // ...
    A* pa;
};

class A { // full declaration
    // ...
    B b;
};

这是你（不是编译器或运行时）负责保持 A 的实例 B 指向（或引用）有效。

It's your (not the compiler or runtime) responsibility to keep the instance of A that instance of B points to (or references) valid.

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