multimap::emplace_hint() in C++ STL

The multimap::emplace_hint() is a built-in function in C++ STL which inserts the key and its element in the multimap container with a given hint. It effectively increases the container size by one as multimap is the container that stores multiple keys with same values. The hint provided does not affect the position to be entered, it only increases the speed of insertion as it points to the position from where the search for the ordering is to be started. It inserts in the same order which is followed by the container. It works similarly to multimap::emplace() function but is at times faster than it if the user provides position accurately. 

Syntax: 

multimap_name.emplace_hint(position, key, element)

Parameters: The function accepts three mandatory parameters key which are described as below:

• key – specifies the key to be inserted in the multimap container.
• element – specifies the element to the key which is to be inserted in the multimap container.
• position – specifies the position from where the search operation for the ordering is to be started, hence making the insertion faster.

Return Value: The function does not return anything. 

CPP

// C++ program to illustrate the
// multimap::emplace_hint() function
#include <bits/stdc++.h>
using namespace std;

int main()
{

    // initialize container
    multimap<int, int> mp;

    // insert elements in random order
    mp.emplace_hint(mp.begin(), 2, 30); // faster
    mp.emplace_hint(mp.begin(), 1, 40); // faster
    mp.emplace_hint(mp.begin(), 2, 60); // slower
    mp.emplace_hint(mp.begin(), 2, 20); // slower
    mp.emplace_hint(mp.begin(), 1, 50); // faster
    mp.emplace_hint(mp.begin(), 1, 50); // faster

    // prints the elements
    cout << "\nThe multimap is : \n";
    cout << "KEY\tELEMENT\n";
    for (auto itr = mp.begin(); itr != mp.end(); itr++)
        cout << itr->first << "\t" << itr->second << endl;

    return 0;
}

Output:

The multimap is : 
KEY    ELEMENT
1    50
1    50
1    40
2    20
2    60
2    30