unordered_multimap emplace() function in C++ STL

The unordered_multimap::emplace() is a built-in function in C++ STL which inserts a new {key, element} in the unordered_multimap container. The insertion is done automatically at the position according to the container’s criterion. It increases the size of the container by one.

Syntax:

unordered_multimap_name.emplace(key, element)

Parameters: The function accepts a single mandatory parameter key and element which is to be inserted in the container.

Return Value: It returns an iterator which points to the newly inserted element.

Below programs illustrates the above function:

Program 1:

// C++ program to illustrate
// unordered_multimap::emplace()
#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;

int main()
{

    // declaration
    unordered_multimap<int, int> sample;

    // inserts key and elements
    sample.emplace(1, 2);
    sample.emplace(1, 2);
    sample.emplace(1, 3);
    sample.emplace(4, 9);
    sample.emplace(60, 89);

    cout << "Key and Elements: \n";
    for (auto it = sample.begin(); it != sample.end(); it++)
        cout << "{" << it->first << ":" << it->second << "}\n ";

    return 0;
}

Output:

Key and Elements: 
 {60:89}
 {4:9}
 {1:3}
 {1:2}
 {1:2}

Program 2:

// unordered_multimap::emplace
#include <iostream>
#include <string>
#include <unordered_map>
using namespace std;

int main()
{

    // declaration
    unordered_multimap<string, string> sample;

    // inserts key and elements
    sample.emplace("gopal", "dave");
    sample.emplace("gopal", "dave");
    sample.emplace("Geeks", "C++");
    sample.emplace("multimap", "functions");
    sample.emplace("multimap", "functions");

    cout << "Key and Elements: \n";
    for (auto it = sample.begin(); it != sample.end(); it++)
        cout << "{" << it->first << ":" << it->second << "}\n ";

    return 0;
}

Output:

Key and Elements: 
 {multimap:functions}
 {multimap:functions}
 {Geeks:C++}
 {gopal:dave}
 {gopal:dave}