multimap::erase() in C++ STL

multimap::erase() is a built-in function in C++ STL which is used to erase element from the container. It can be used to erase keys, elements at any specified position or a given range.
1. Syntax for erasing a key:

   multimap_name.erase(key)
   

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

   Return Value: The function does not return anything. It erases all the elements with the specified key.

   // C++ program to illustrate
   // multimap::erase(key)
   #include <bits/stdc++.h>
   using namespace std;
   
   int main()
   {
   
       // initialize container
       multimap<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 multimap 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 multimap after applying erase() is : \n";
       cout << "KEY\tELEMENT\n";
       for (auto itr = mp.crbegin(); itr != mp.crend(); ++itr) {
           cout << itr->first
                << '\t' << itr->second << '\n';
       }
       return 0;
   }
   Output:

   The multimap before using erase() is : 
   KEY    ELEMENT
   1    40
   2    30
   2    20
   3    60
   5    50
   
   The multimap after applying erase() is : 
   KEY    ELEMENT
   5    50
   3    60
   

2. Syntax for removing a position:

   multimap_name.erase(iterator position)
   

   Parameters: The function accept 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 returns anything.

   Program below illustrate the above syntax:

   // C++ program to illustrate
   // multimap::erase(position)
   #include <bits/stdc++.h>
   using namespace std;
   
   int main()
   {
   
       // initialize container
       multimap<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 multimap 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 multimap after applying erase() is : \n";
       cout << "KEY\tELEMENT\n";
       for (auto itr = mp.crbegin(); itr != mp.crend(); ++itr) {
           cout << itr->first
                << '\t' << itr->second << '\n';
       }
       return 0;
   }
   Output:

   The multimap before using erase() is : 
   KEY    ELEMENT
   1    40
   2    30
   2    20
   3    60
   5    50
   
   The multimap after applying erase() is : 
   KEY    ELEMENT
   3    60
   2    20
   1    40
   

3. Syntax for erasing a given range:

   multimap_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 upto which removal is to be done.

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

   Program below illustrate the above syntax:

   // C++ program to illustrate
   // multimap::erase()
   #include <bits/stdc++.h>
   using namespace std;
   
   int main()
   {
   
       // initialize container
       multimap<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 multimap 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 multimap after applying erase() is : \n";
       cout << "KEY\tELEMENT\n";
       for (auto itr = mp.crbegin(); itr != mp.crend(); ++itr) {
           cout << itr->first
                << '\t' << itr->second << '\n';
       }
       return 0;
   }
   Output:

   The multimap before using erase() is : 
   KEY    ELEMENT
   1    40
   2    30
   2    20
   3    60
   5    50
   
   The multimap after applying erase() is : 
   KEY    ELEMENT
   5    50
   1    40