【C++】unorder_map

1、插入

umap["Practice"] = 20;
//or
umap.insert(make_pair("Code", 50));

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

int main()
{
    
    
    unordered_map<string, int> umap;

    // inserting values by using [] operator
    umap["GeeksforGeeks"] = 10;
    umap["Practice"] = 20;
    umap["Contribute"] = 30;

    // inserting values by using insert() method
    umap.insert(make_pair("Quiz", 40));
    umap.insert(make_pair("Code", 50));

    cout << "The unordered map is : \n";
    cout << "KEY\tELEMENT\n";

    for (auto itr = umap.begin(); itr != umap.end(); itr++) {
    
    
        cout << itr->first
             << '\t' << itr->second << '\n';
    }
}

2、修改

umap["Practice"] = 40;

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

int main()
{
    
    
    unordered_map<string, int> umap;

    // inserting values by using [] operator
    umap["GeeksforGeeks"] = 10;
    umap["Practice"] = 20;
    umap["Contribute"] = 30;

    // modifying value by using [] operator
    umap["Practice"] = 40;

    cout << "The unordered map is : \n";
    cout << "KEY\tELEMENT\n";

    for (auto itr = umap.begin(); itr != umap.end(); itr++) {
    
    
        cout << itr->first
             << '\t' << itr->second << '\n';
    }
}

3、删除

umap.erase("Practice");

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

int main()
{
    
    
    unordered_map<string, int> umap;

    // inserting values by using [] operator
    umap["GeeksforGeeks"] = 10;
    umap["Practice"] = 20;
    umap["Contribute"] = 30;

    // erasing by using key value
    umap.erase("Practice");

    cout << "The unordered map is : \n";
    cout << "KEY\tELEMENT\n";

    for (auto itr = umap.begin(); itr != umap.end(); itr++) {
    
    
        cout << itr->first
             << '\t' << itr->second << '\n';
    }
}