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map cbegin() and cend() function in C++ STL

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  • Difficulty Level : Basic
  • Last Updated : 17 Jun, 2022
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map::cbegin() is a built-in function in C++ STL that returns a constant iterator referring to the first element in the map container. Since map container contains the element in an ordered way, cbegin() will point to that element that will come first according to the container’s sorting criterion.

Syntax: 

map_name.cbegin()

Parameters: The function does not accept any parameter.

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

CPP




// C++ program to illustrate
// the map::cbegin() function
#include& lt; bits / stdc++.h & gt;
using namespace std;
 
int main()
{
 
    // initialize container
    map& lt;
    int, int& gt;
    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.cbegin();
 
    cout& lt;
    <
    "
    The first element is : "
    ;
    cout& lt;
    <
    "
    {
        "
        <
        <
        ite - >
        first& lt;
        <
        "
        , "
        <
        <
        ite - >
        second& lt;
        <
        "
    }
    \n& quot;
    ;
 
    // prints the elements
    cout& lt;
    <
    "
    \nThe map is : \n& quot;
    ;
    cout& lt;
    <
    "
    KEY\tELEMENT\n& quot;
    ;
    for (auto itr = mp.cbegin(); itr != mp.cend(); ++itr) {
        cout& lt;
        <
        itr - >
        first& lt;
        <
        '\t' & lt;
        <
        itr - >
        second& lt;
        <
        '\n';
    }
    return 0;
}

Output:

The first element is: {1, 40}

The map is : 
KEY    ELEMENT
1    40
2    30
3    60
4    20
5    50

map::cend() is a built-in function in C++ STL that returns a constant iterator pointing to the theoretical element that follows the last element in the multimap. Since map container contains the element in an ordered way, cend() will point to that follows the last element according to the container’s sorting criterion. 

Syntax: 

map_name.cend()

Parameters: The function does not accept any parameter.

Return Value: The function returns a constant iterator pointing to the theoretical element that follows the last element in the map. 

CPP




// C++ program to illustrate
// the map::cend() 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 });
 
    // print the elements
    cout << "\nThe map is : \n";
    cout << "KEY\tELEMENT\n";
    for (auto itr = mp.cbegin(); itr != mp.cend(); ++itr) {
        cout << itr->first
             << '\t' << itr->second << '\n';
    }
    return 0;
}

Output:

The map is : 
KEY    ELEMENT
1    40
2    30
3    60
4    20
5    50

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

map cbegin()map cend()
It is used to return a const_iterator pointing to the first element in the container.It is used to return a const_iterator pointing to the past-the-end element in the container.

Its syntax is as follows:

const_iterator cbegin() const

Its syntax is as follows:

const_iterator cend() const
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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