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list::pop_front() and list::pop_back() in C++ STL

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  • Difficulty Level : Basic
  • Last Updated : 23 Jun, 2022
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Lists are containers used in C++ to store data in a non contiguous fashion, Normally, Arrays and Vectors are contiguous in nature, therefore the insertion and deletion operations are costlier as compared to the insertion and deletion option in Lists.

list::pop_front()

pop_front() function is used to pop or remove elements from a list from the front. The value is removed from the list from the beginning, and the container size is decreased by 1. Syntax :

listname.pop_front()
Parameters :
No argument is passed as parameter.
Result :
Removes the value present at the front 
of the given list named as listname

Examples:

Input :  list list{1, 2, 3, 4, 5};
         list.pop_front();
Output : 2, 3, 4, 5

Input :  list list{5, 4, 3, 2, 1};
         list.pop_front();
Output : 4, 3, 2, 1

Errors and Exceptions

  1. No-Throw-Guarantee – if an exception is thrown, there are no changes in the container.
  2. If the list is empty, it shows undefined behaviour.

CPP




// CPP program to illustrate
// pop_front() function
#include <iostream>
#include <list>
using namespace std;
 
int main()
{
    list<int> mylist{ 1, 2, 3, 4, 5 };
    mylist.pop_front();
 
    // list becomes 2, 3, 4, 5
 
    for (auto it = mylist.begin(); it != mylist.end(); ++it)
        cout << ' ' << *it;
}

Output:

2, 3, 4, 5

Application : Input an empty list with the following numbers and order using push_front() function and print the reverse of the list.

Input : 1, 2, 3, 4, 5, 6, 7, 8
Output: 8, 7, 6, 5, 4, 3, 2, 1

CPP




// CPP program to illustrate
// application Of pop_front() function
#include <iostream>
#include <list>
using namespace std;
 
int main()
{
    list<int> mylist{}, newlist{};
    mylist.push_front(8);
    mylist.push_front(7);
    mylist.push_front(6);
    mylist.push_front(5);
    mylist.push_front(4);
    mylist.push_front(3);
    mylist.push_front(2);
    mylist.push_front(1);
 
    // list becomes 1, 2, 3, 4, 5, 6, 7, 8
 
    while (!mylist.empty()) {
        newlist.push_front(mylist.front());
        mylist.pop_front();
    }
    for (auto it = newlist.begin(); it != newlist.end(); ++it)
        cout << ' ' << *it;
}

Output:

8, 7, 6, 5, 4, 3, 2, 1
list::pop_back()

pop_back() function is used to pop or remove elements from a list from the back. The value is removed from the list from the end, and the container size is decreased by 1. Syntax :

listname.pop_back()
Parameters :
No argument is passed as parameter.
Result :
Removes the value present at the end or back 
of the given list named as listname

Examples:

Input :  list list{1, 2, 3, 4, 5};
         list.pop_back();
Output : 1, 2, 3, 4

Input :  list list{5, 4, 3, 2, 1};
         list.pop_back();
Output : 5, 4, 3, 2

Errors and Exceptions

  1. No-Throw-Guarantee – if an exception is thrown, there are no changes in the container.
  2. If the list is empty, it shows undefined behaviour.

CPP




// CPP program to illustrate
// pop_back() function
#include <iostream>
#include <list>
using namespace std;
 
int main()
{
    list<int> mylist{ 1, 2, 3, 4, 5 };
    mylist.pop_back();
 
    // list becomes 1, 2, 3, 4
 
    for (auto it = mylist.begin(); it != mylist.end(); ++it)
        cout << ' ' << *it;
}

Output:

1, 2, 3, 4

Application : Input an empty list with the following numbers and order using push_front() function and print the reverse of the list.

Input : 1, 20, 39, 43, 57, 64, 73, 82
Output: 82, 73, 64, 57, 43, 39, 20, 1

CPP




// CPP program to illustrate
// application Of pop_back() function
#include <iostream>
#include <list>
using namespace std;
 
int main()
{
    list<int> mylist{}, newlist{};
    mylist.push_front(82);
    mylist.push_front(73);
    mylist.push_front(64);
    mylist.push_front(57);
    mylist.push_front(43);
    mylist.push_front(39);
    mylist.push_front(20);
    mylist.push_front(1);
 
    // list becomes 1, 20, 39, 43, 57, 64, 73, 82
 
    while (!mylist.empty()) {
        newlist.push_back(mylist.back());
        mylist.pop_back();
    }
    for (auto it = newlist.begin(); it != newlist.end(); ++it)
        cout << ' ' << *it;
}

Output:

82, 73, 64, 57, 43, 39, 20, 1

Let us see the differences in a tabular form -:

 list::pop_front()list::pop_back()
1.It is used to remove the first element in the list containerIt is used to remove the last element in the list container
2.

Its syntax is -:

 pop_front();

Its syntax is -:

pop_back();

3.It does not take any parameters.It does not take any parameters.
4.It does not have any return type.It does not have any return type.
5.Its complexity is constant.Its complexity is constant.

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