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map crbegin() and crend() function in C++ STL

  • Difficulty Level : Basic
  • Last Updated : 29 Jun, 2018
  1. map::crbegin() is a built-in function in C++ STL which returns a constant reverse iterator referring to the last element in the map container. Since map container contains the element in an ordered way, crbegin() will point to that element that will come last according to the container’s sorting criterion.

    Syntax:

    map_name.crbegin()
    

    Parameters: The function does not accept any parameter.

    Return Value: The function returns a constant reverse iterator referring to the last element in the map container.




    // C++ program to illustrate
    // map::crbegin() function
    #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({ 4, 20 });
        mp.insert({ 5, 50 });
      
        auto ite = mp.crbegin();
        cout << "The last element is {" << ite->first
             << ", " << ite->second << "}\n";
      
        // prints the elements
        cout << "\nThe map in reverse order 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 last element is {5, 50}
    
    The map in reverse order is: 
    KEY    ELEMENT
    5    50
    4    20
    3    60
    2    30
    1    40
    
  2. map::crend() is a built-in function in C++ STL which returns a constant reverse iterator pointing to the theoretical element before the first element in the map. Since map container contains the element in an ordered way, crend() will point to the element theoretically before the first element according to the container’s sorting criterion.

    Syntax:

    map_name.crend()
    

    Parameters: The function does not accept any parameter.

    Return Value: The function returns a constant reverse iterator pointing to the theoretical element before the first element in the map.




    // C++ program to illustrate 
    // map::crend() function
    #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({ 4, 20 });
        mp.insert({ 5, 50 });
      
        // prints the elements
        cout << "\nThe map in reverse order 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 map in reverse order is : 
    KEY    ELEMENT
    5    50
    4    20
    3    60
    2    30
    1    40
    


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