How to Insert a Pair into an Unordered Map in C++?

In C++, STL provides the pair container which allows the user to store two objects that can be of the same or different type as a single unit. On the other hand, the Unordered Map is a data structure that stores the data in the form of key-value pairs where the keys must be unique. In this article, we will learn how we can insert a Pair into an Unordered Map in C++.

Example:

Input: 
myUnorderedMap = { {1,"Geek"}, {2, "for"} }
Output:
myUnorderedMap= { {1,"Geek"}, {2, "for"}, {3,"Geeks"} }
// pairs inserted into the unordered map

Insert a Pair into an Unordered Map in C++

To insert a std::pair into a std::unordered map in C++, we can simply use the std::unordered_map::insert() method to insert the pair into the unordered map. It is a member function of the std::unordered_map class and only need to pass the said pair as an argument to it.

Note: We must ensure the pair data type matches with the data type of the unordered map.

C++ Program to Insert a Pair into an Unordered Map

// C++ program to insert a pair into an unordered map
#include <iostream>
#include <unordered_map>
using namespace std;

int main()
{
    // declare an unordered map
    unordered_map<int, string> mp
        = { { 1, "Geek" }, { 2, "for" } };

    // Create the pairs you want to insert
    pair<int, string> pair3 = make_pair(3, "Geeks");

    // Insert the pairs into the unordered map using
    // insert() function

    mp.insert(pair3);

    // Print the unordered map

    for (auto& pair : mp) {
        cout << pair.first << ": " << pair.second << endl;
    }

    return 0;
}

3: Geeks
2: for
1: Geek

Time Complexity: O(1), worst case O(n), where n is the number of elements in the unordered_pair
Auxilary Space: O(1)

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Article Tags :

• C++ Programs
• C++
• STL
• cpp-unordered_map
• cpp-pair
• CPP Examples

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Practice Tags :

• CPP
• STL