c++ unordered_map合并

我想合併兩個std::unordered_map:mapA和mapB，同時如果兩個 map 都包含相同的鍵，則保留mapA中專案的優先順序。https://www.796t.com/post/NHFoYjI=.html

例:
mapA = {{"sugar",0.1},{"salt",0.2}}
mapB = {{"sugar",0.3},{"pepper",0.4}}

结果:
result = {{"sugar",0.1},{"salt",0.2},{"pepper",0.4}}

{"sugar",0.3}忽略mapB

解决办法
auto result = mapA;
result.insert(mapB.begin(), mapB.end());

#include <iostream>
#include <unordered_map>
using namespace std;

int main() {
    unordered_map<string,double> mapA = {{"sugar",0.1},{"salt",0.2}};
    unordered_map<string,double> mapB = {{"sugar",0.3},{"pepper",0.4}};
    mapA.insert(mapB.begin(), mapB.end());
    for (auto &i : mapA) {
        cout << i.first << " " << i.second << endl;
    }
    return 0;
}