map erase() function in C++ STL

map::erase() is a built-in function in C++ STL that is used to erase elements from the container. It can be used to erase keys and elements at any specified position or a given range. 

• The syntax for erasing a key:

map_name.erase(key)

Parameters: The function accepts one mandatory parameter key which specifies the key to be erased in the map container. 

Return Value: The function returns 1 if the key element is found in the map else returns 0. 

The below program illustrate the above syntax: 

C++

// C++ program to illustrate
// map::erase(key)
#include <bits/stdc++.h>
using namespace std;

int main()
{

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

    // insert elements in random order
    mp.insert({ 2, 30 });
    mp.insert({ 1, 40 });
    mp.insert({ 3, 60 });
    mp.insert({ 5, 50 });

    // prints the elements
    cout << "The map before using erase() is : \n";
    cout << "KEY\tELEMENT\n";
    for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
        cout << itr->first
             << '\t' << itr->second << '\n';
    }

    // function to erase given keys
    mp.erase(1);
    mp.erase(2);

    // prints the elements
    cout << "\nThe map after applying erase() is : \n";
    cout << "KEY\tELEMENT\n";
    for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
        cout << itr->first
             << '\t' << itr->second << '\n';
    }
    return 0;
}

Output

The map before using erase() is : 
KEY    ELEMENT
1    40
2    30
3    60
5    50

The map after applying erase() is : 
KEY    ELEMENT
3    60
5    50

Time Complexity: O(1) or Amortized constant

• The syntax for removing a position: 

map_name.erase(iterator position)

Parameters: The function accepts one mandatory parameter position which specifies the iterator that is the reference to the position of the element to be erased. 

Return Value: The function does not return anything. 

The below program illustrate the above syntax: 

C++

// C++ program to illustrate
// map::erase(iteratorposition)
#include <bits/stdc++.h>
using namespace std;

int main()
{

    // initialize container
    map<int, int> mp;
    // insert elements in random order
    mp.insert({ 2, 30 });
    mp.insert({ 1, 40 });
    mp.insert({ 3, 60 });
    mp.insert({ 5, 50 });

    // prints the elements
    cout << "The map before using erase() is : \n";
    cout << "KEY\tELEMENT\n";
    for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
        cout << itr->first
             << '\t' << itr->second << '\n';
    }

    // function to erase given position
    auto it = mp.find(2);
    mp.erase(it);

    auto it1 = mp.find(5);
    mp.erase(it1);

    // prints the elements
    cout << "\nThe map after applying erase() is : \n";
    cout << "KEY\tELEMENT\n";
    for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
        cout << itr->first
             << '\t' << itr->second << '\n';
    }
    return 0;
}

Output

The map before using erase() is : 
KEY    ELEMENT
1    40
2    30
3    60
5    50

The map after applying erase() is : 
KEY    ELEMENT
1    40
3    60

Time Complexity: O(n)

• The syntax for erasing a given range: 

map_name.erase(iterator position1, iterator position2)

Parameters: The function accepts two mandatory parameters which are described below: 

• position1 – specifies the iterator that is the reference to the element from which removal is to be done.
• position2 – specifies the iterator that is the reference to the element up to which removal is to be done.

Return Value: The function does not return anything. It removes all the elements in the given range of iterators.

The program below illustrates the above syntax: 

C++

// C++ program to illustrate
// map::erase(iteratorposition1, iteratorposition2)
#include <bits/stdc++.h>
using namespace std;

int main()
{

    // initialize container
    map<int, int> mp;
    // insert elements in random order
    mp.insert({ 2, 30 });
    mp.insert({ 1, 40 });
    mp.insert({ 3, 60 });
    mp.insert({ 2, 20 });
    mp.insert({ 5, 50 });

    // prints the elements
    cout << "The map before using erase() is : \n";
    cout << "KEY\tELEMENT\n";
    for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
        cout << itr->first
             << '\t' << itr->second << '\n';
    }

    // function to erase in a given range
    // find() returns the iterator reference to
    // the position where the element is
    auto it1 = mp.find(2);
    auto it2 = mp.find(5);
    mp.erase(it1, it2);

    // prints the elements
    cout << "\nThe map after applying erase() is : \n";
    cout << "KEY\tELEMENT\n";
    for (auto itr = mp.begin(); itr != mp.end(); ++itr) {
        cout << itr->first
             << '\t' << itr->second << '\n';
    }
    return 0;
}

Output

The map before using erase() is : 
KEY    ELEMENT
1    40
2    30
3    60
5    50

The map after applying erase() is : 
KEY    ELEMENT
1    40
5    50

Time Complexity: O(last – first)