Question

我正在实施六度Kevin Bacon问题并为actor节点编写一个类。我可以使用set而不是hash_set容器来保存用户定义的类。为什么？错误消息显示：错误C2440：'type cast'：无法从'const ActorGraphNode'转换为'size_t' 1 GT;没有可用于执行此转换的用户定义转换运算符，或者无法调用运算符....

#include <hash_set>
#include <set>
class ActorGraphNode{
    public: 
    string ActorName;
    //hash_set<ActorGraphNode> linkedActors;
    set<ActorGraphNode> linkedActors;
    ActorGraphNode(string name):ActorName(name){}
    void linkCostar(ActorGraphNode actor){
       linkedActors.insert(actor);
       actor.linkedActors.insert(*this);
    }
    bool operator<( const ActorGraphNode& a ) const
    { return ActorName < a.ActorName ? true : false;}
};

Answer 1

不出所料，hash_set要求您为您的类型实现哈希函数。

class ActorGraphNode{
    public: 
    string ActorName;
    hash_set<ActorGraphNode> linkedActors;
    //set<ActorGraphNode> linkedActors;
    ActorGraphNode(string name):ActorName(name){}
    void linkCostar(ActorGraphNode actor){
       linkedActors.insert(actor);
       actor.linkedActors.insert(*this);
    }
    bool operator<( const ActorGraphNode& a ) const
    { return ActorName < a.ActorName;}
    bool operator ==( const ActorGraphNode& a ) const
    { return ActorName == a.ActorName;}
    operator size_t() const
    {
      return hash<string>()(ActorName);
    }
};

Answer 2

感谢所有人的回答和评论。这是我的更新代码，在您的帮助下。加上函数linkCostar（）我现在使用传递引用：

class ActorGraphNode{
public: 
    string ActorName;
    hash_set<ActorGraphNode> linkedActors;
    ActorGraphNode(string name):ActorName(name){}
    void linkCostar(ActorGraphNode& actor){
        linkedActors.insert(actor);
        actor.linkedActors.insert(*this);
    }
    bool operator==( const ActorGraphNode& a ) const
    { return ActorName == a.ActorName ? true : false;}
    operator size_t() const
    {
        const int HASHSIZE = 501;
        int seed = 131;
        size_t sum = 0;
        for(size_t i = 0; i < ActorName.length(); ++i) 
            sum = (sum * seed) + ActorName[i];      
        return sum % HASHSIZE;
    }
};

不能在hash_set中包含用户定义的类

2 个答案: