c++ - hash_set 中不能包含用户定义的类

Question

我正在实现六度 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？错误信息显示:error C2440: 'type cast' : cannot convert from 'const ActorGraphNode' to 'size_t'1> 没有可用的可以执行此转换的用户定义转换运算符，或者无法调用该运算符....

#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);
    }
};