How to Delete a Pair from an Unordered Map in C++?

In C++, the unordered_map is like a dictionary that stores data in the form of key-value pairs. In this article, we will learn how to delete a key-value pair from an unordered_map in C++.

Example

Input:
mp={ {1,"Apple"}, {3,"Mango"},{2,"Orange"}}
Key= 3

Output:
Map after deleting key:
1: Apple
2: Orange

Remove Key-Value Pair from Unordered Map in C++

In unordered_map, we can delete a pair by using the std::unordered_map::erase() method. First, we check if a key for a pair that you want to delete exists or not. If it exists, then we remove it by simply passing that key to the erase() function.

C++ Program to Delete a Pair from Unordered Map

C++

// C++ program to delete pair from unordered map
#include <iostream>
#include <unordered_map>

using namespace std;

int main()
{
    // Create an unordered_map
    unordered_map<int, string> myUnorderedMap;

    // Insert some elements
    myUnorderedMap[1] = "Apple";
    myUnorderedMap[3] = "Mango";
    myUnorderedMap[2] = "Orange";

    // Find the iterator for key
    int key = 3;
    auto iter = myUnorderedMap.find(key);

    // Delete the pair with key if found
    if (iter != myUnorderedMap.end()) {
        myUnorderedMap.erase(iter);
    }

    // Display elements after deletion
    cout << "\nUnordered Map after deletion:" << endl;
    for (const auto& pair : myUnorderedMap) {
        cout << pair.first << ": " << pair.second << endl;
    }

    return 0;
}

Output

Unordered Map after deletion:
2: Orange
1: Apple

Time Complexity: O(N) is worst case time complexity, while the average complexity is O(1).
Auxiliary Space: O(1)

Note: We can also use clear() function to delete key-value pair from a unordered map.