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

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  • Difficulty Level : Basic
  • Last Updated : 17 Jun, 2022

map::crbegin() is a built-in function in C++ STL that 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. 

Example:

CPP




// 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

map::crend() is a built-in function in C++ STL that 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. 

Example

CPP




// 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

Let us see the differences in a tabular form as shown below as follows:

map crbegin()map crend()
It is used to return a const_reverse_iterator pointing to the last element in the container.It is used to return a const_reverse_iterator pointing to the theoretical element preceding the first element in the container.

Its syntax is as follows:

const_reverse_iterator crbegin()

Its syntax is as follows:

const_reverse_iterator crend()
It does not take any parameters.It does not take any parameters.
Its complexity is constant.Its complexity is constant.
Its iterator validity does not change.Its iterator validity does not change.

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