c++ - 在类(class)之间共享信息

Question

我正在尝试使用来自 here 的信息在类(class)之间共享信息,除了我无法编译这两个类，因此相互沟通。

所以，我想要的是让 ClassB 获得对 ClassA 的引用，并且ClassB 在 ClassA 中初始化。

编译器错误(使用 g++):

In member function 'void ClassA::foo()':
hello.cpp:9: error: 'ClassB' was not declared in this scope
hello.cpp:9: error: 'someB' was not declared in this scope
hello.cpp:9: error: expected type-specifier before 'ClassB'
hello.cpp:9: error: expected ';' before 'ClassB'

然后我尝试在 ClassA 之前添加 class ClassB;，

喜欢:

class ClassB; // just this here.

class ClassA; // all of classA here.

class ClassB; // all of classB here.

然后我得到:

hello.cpp: In member function 'void ClassA::foo()':
hello.cpp:11: error: invalid use of incomplete type 'struct ClassB'
hello.cpp:3: error: forward declaration of 'struct ClassB'
hello.cpp:12: error: invalid use of incomplete type 'struct ClassB'
hello.cpp:3: error: forward declaration of 'struct ClassB'

---

这是我基于上述网站尝试使用的代码:

include stdio.h

class ClassA {
    public:
        void foo() {
            ClassB *someB = new ClassB();
            someB->setRelative(this);
        }

        void bar() {
            printf("B is communicating with me =)\n");
        }
};

---

class ClassB {

    ClassA *m_relative;

    public:
        void setRelative(ClassA *other) {
            this->m_relative = other;
        }

        void foo() {
            m_relative->bar();
        }
};

Answer 1

你显然在这里有一个循环依赖，你不能只使用标题来真正解决这个问题(可能有一些宏技巧，但我不会担心)。

您应该做的是将您的代码拆分为声明( header )和实现。

啊啊

// only include this file once per translation unit
#pragma once

// tell the compiler B is going to be a class,
// so B* is a pointer to a class - nothing more is needed for now.
class B;

// full declaration of A
class A {
    B *child;

public:
    A(void);
}

a.cpp

#include "a.h" // included whenever the structure/size of A has to be known
#include "b.h" // same for B

A::A(void) : child(new B(this)) {
    // do something with child or...
    B * = new B(this);
}

b.h

// only include this file once per translation unit
#pragma once

// again, just tell the compiler A is going to be a class
class A;

class B {
    A *parent;
public:
    B(A *pparent);
}

b.cpp

#include "a.h"
#include "b.h"

B::B(A *pparent) : parent(pparent) {
    // do something with parent
}