c ++：从容器中删除元素并将其取回

Question

是否有一个内置方法可以删除和元素（即从给定键的映射中）并返回被删除的元素？

Answer 1

There is no built-in method to do this, you can however store the element by accessing it and then erase it. Erasing requires you to specify key.If it's a multi-map you should erase with position.

Answer 2

Here is a function you can use (C++11):

#include <iostream>
#include <map>

template<typename T>
typename T::mapped_type removeAndReturn(T& mp, const typename T::key_type& val) {
    auto it = mp.find(val);
    auto value = std::move(it->second);
    mp.erase(it);
    return value;
}

int main() {
    std::map<int, int> m;
    m[3] = 4;
    std::cout << "Map is empty: " << std::boolalpha << m.empty() << std::endl;
    std::cout << "Value returned: " << rm_and_return(m, 3) << std::endl;
    std::cout << "Map is empty: " << std::boolalpha << m.empty() << std::endl;
}

Output:

Map is empty: false
Value returned: 4
Map is empty: true