C ++类中的循环依赖 [英] Circular dependency in C++ classes

问题描述

我对C ++比较陌生，面对着一个循环依赖的问题。有人可以帮我解决这个问题吗？

I am relatively new to C++, and facing a circular dependency problem. Can someone please help me solve this?

我有两个课程：

class Vertex {
    string name;
    int distance;
    //Vertex path;
    int weight;
    bool known;
    list<Edge> edgeList;
    list<Vertex> adjVertexList;

public:
    Vertex();
    Vertex(string nm);
    virtual ~Vertex();
};

class Edge {
    Vertex target;
    int weight;

public:
    Edge();
    Edge(Vertex v, int w);
    virtual ~Edge();

    Vertex getTarget();
    void setTarget(Vertex target);
    int getWeight();
    void setWeight(int weight);
};

上述代码提供以下错误：

The above code gives following errors:

• '顶点'未命名类型


• '顶点'未声明


• 'v'

如何解决此问题？

推荐答案

所有你需要的是在顶点 Edge >：

All you need is to forward-declare the Edge class before it's used within the Vertex:

class Edge;

class Vertex {
    string name;
    int distance;
    ...
};

class Edge { ... };

不能放置类型顶点而不是 Vertex 本身的声明，因为C ++不允许递归类型。在C ++的语义中，这种类型的大小需要是无限的。

You can't put members of type Vertex instead of the declaration of Vertex itself, since C++ doesn't allow recursive types. Within the semantics of C++, the size of such type would need to be infinite.

当然，你可以把指针放在 code> 顶点。

You can, of course, put pointers to Vertex within Vertex.

你想要什么，其实在顶点的边和邻接表，是指针，而不是对象的副本。因此，你的代码应该如下修改（假设你使用C ++ 11，你实际上应该使用现在）：

What you want, in fact, within Vertex's edge and adjacency lists, is pointers, not copies of objects. Thus, your code should be fixed like below (assuming you use C++11, which you in fact should be using now):

class Edge;

class Vertex {
    string name;
    int distance;
    int weight;
    bool known;
    list<shared_ptr<Edge>> edgeList;
    list<shared_ptr<Vertex>> adjVertexList;

public:
    Vertex();
    Vertex(const string & nm);
    virtual ~Vertex();
};

class Edge {
    Vertex target;
    int weight;

public:
    Edge();
    Edge(const Vertex & v, int w);
    virtual ~Edge();

    Vertex getTarget();
    void setTarget(const Vertex & target);
    int getWeight();
    void setWeight(int weight);
};

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