我有这样无序的地图:
static std::unordered_map<std::pair<size_t , size_t>, long> my_map;
然后我想从my_map
得到价值:
size_t size1 = 1;
size_t size2 = 2;
auto x = make_pair(size1, size2);
auto &result = my_map[x];
但我有一个错误:
error: no match for ‘operator[]’ (operand types are ‘std::unordered_map<std::pair<long unsigned int, long unsigned int>, long int>’ and ‘std::pair<long unsigned int, long unsigned int>’)
auto &result = my_map[x];
我怎样才能克服它?
答案 0 :(得分:0)
使用here中的哈希函数:
#include <unordered_map>
#include <utility>
#include <map>
#include <functional>
#include <string>
// Only for pairs of std::hash-able types for simplicity.
// You can of course template this struct to allow other hash functions
struct pair_hash {
template <class T1, class T2>
std::size_t operator () (const std::pair<T1, T2> &p) const {
auto h1 = std::hash<T1>{}(p.first);
auto h2 = std::hash<T2>{}(p.second);
// Mainly for demonstration purposes, i.e. works but is overly simple
// In the real world, use sth. like boost.hash_combine
return h1 ^ h2;
}
};
int main()
{
//static std::unordered_map<std::pair<size_t, size_t>, long> my_map;
static std::unordered_map<std::pair<size_t, size_t>, long, pair_hash> my_map;
size_t size1 = 1;
size_t size2 = 2;
auto x = std::make_pair(size1, size2);
auto &result = my_map[x];
return 0;
}