所以我正在尝试将 Graph 类作为另一个项目的一部分。顶点存储在由 unordered_map 定义的邻接表中。我正在尝试创建一个散列函数以允许我的 Vertex 类存储在此 map 中,但我不知道我做错了什么。我收到此错误:
no matching function for call to ‘std::hash<Vertex<int> >::hash(int)’
这是我的 graph.h 文件
#ifndef GRAPH_GRAPH_H_
#define GRAPH_GRAPH_H_
#include <vector>
#include <unordered_map>
template <typename T>
class Vertex {
private:
T value;
public:
Vertex(T value);
T getValue() const;
void setValue(T value);
//Equality check. This also requires an equality check to exist for T. If it does not (e.g. custom class), make sure you impemented one
bool operator==(const Vertex<T>& v) const{
return (this->value == v.value);
}
};
template <typename T>
Vertex<T>::Vertex(T value) {
this->value = value;
}
template <typename T>
T Vertex<T>::getValue() const{
return this->value;
}
template <typename T>
void Vertex<T>::setValue(T value) {
this->value = value;
}
//If you want to hash a vertex, T needs a way of being hashed
namespace std {
template<typename T> struct hash<Vertex<T>> {
size_t operator()(Vertex<T> const& v) const {
return hash(v.getValue());
}
};
}
template <typename T>
class Graph {
private:
//Now I know what you're thinking. Graph theory taught me that a graph needs a set of nodes, and an adjacency list.
//All you've given us is an adjacency list.
//Well, since we need to use our nodes as keys, the set of keys is equivalent to the set of nodes. So there.
unordered_map<Vertex<T>, std::vector<Vertex<T>>> adjacencyList;
public:
Graph(); //Needs a hash function. For example, if your vertices are storing std::pairs, we need a hash to convert the pair into a key
//Since I don't know what you will be storing, you should provide a hash function
~Graph();
//Since we are initialising a new object, v must be whatever we are using to initialise our vertices
void addVertex(T value, std::vector<T> adjacent);
void removeVertex(T value);
void printGraph();
};
template <typename T>
Graph<T>::Graph() {
}
template <typename T>
Graph<T>::~Graph() {
}
template <typename T>
void Graph<T>::addVertex(T value, std::vector<T> adjacent) {
//Check that the value does not already exist
if (this->adjacencyList.find(Vertex<T>(value)) == this->adjacencyList.end()) {
Vertex<T> v = Vertex<T>(value);
std::vector<Vertex<T>> adj;
for (unsigned int i = 0; i < adjacent.size(); i++) {
Vertex<T> vAdj = Vertex<T>(adjacent[i]);
adj.push_back(vAdj);
}
this->adjacencyList.insert(make_pair(v, adj));
}
//If the values does not exist, place it and the adjacency in there
//Otherwise, do nothing
}
template <typename T>
void Graph<T>::removeVertex(T value) {
//Check that the value does not already exist
//if (this->adjacencyList.find(Vertex<T>(value)) != this->adjacencyList.end()) {
this->adjacencyList.erase(Vertex<T>(value));
//}
}
template <typename T>
void Graph<T>::printGraph() {
}
#endif /* GRAPH_GRAPH_H_ */
最佳答案
你有一个错误
return hash(v.getValue());
std::hash
不是一个函数,它是一个结构体,所以你需要先创建一个对象。例如
return hash<T>{}(v.getValue());
关于C++:无法为 Vertex 对象创建哈希函数,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/44403822/