C++ STL List

Introduction

C++ STL List

In this article, you will learn about the list container of STL (Standard Template Library) of C++ with some useful examples that would help you better understand the concepts and their usage.

Lists are a type of sequential container that allows non-contiguous memory allocation. If we compare the list to a vector, the list has slow traversal as the memory allocated is non-contiguously. But when the position is known the insertion and deletion of the elements are done quickly. A list is like a doubly linked list.

We use the header file <list> to use the functionalities of an STL list container class. The syntax for declaring a list is given below:

Syntax: list<data_type> list_name;

As we already know that all the containers in the STL are generic types, so we must specify the data type while declaring a container.

A list has many methods for performing different types of operations. A few of the methods are listed below:

• front() – Returns the value of the first element in the list.
• back() – Returns the value of the last element in the list.
• push_front(i) – Adds the new element ‘i’ at the beginning of the list.
• push_back(i) – Adds the new element ‘i’ at the end of the list.
• pop_front()  – Removes the first element of the list, and reduces the size of the list by 1.
• pop_back() – Removes the last element of the list, and reduces the size of the list by 1.
• List_name.begin() – Returns an iterator pointing to the first element of the list.
• List_name.end() – Returns an iterator pointing to the theoretical last element which follows the last element of the list.
• List_name.rbegin() – Returns the reverse iterator pointing to the last element of the list.
• List_name.rend() – Returns the reverse iterator pointing to the theoretically first element in the list which is before the actual first element of the list.
• List_name.cbegin() – Returns a constant iterator pointing to the first element of the list i.e., the value pointed at cannot be changed.
• List_name.cend()  – Returns a constant iterator pointing to the end of the list.
• List_name.crbegin() – Returns a constant reverse iterator that points to the last element of the list i.e., reversed beginning of the container.
• List_name.crend() – Returns a constant reverse iterator that points to the first element of the list i.e., reversed ending of the container.

• empty() – Returns whether or not a list is empty. Returns true if the list is empty if not returns false.
• insert(i) – inserts a new element ‘i’ into the list before the element at a specified position.
• erase() – Removes a single element or a range of elements from the list.
• assign(new_list) – Assigns new elements to the list replacing the current elements and resizes the list.
• remove(i) – Removes all the elements from the list, which is equal to the given element ‘i’.
• size() – Returns the number of elements in the list.
• list_resize() – Used to resize a list container.
• sort() – Sorts the list in ascending order.
• list_max_size() – Returns the maximum number of elements a list container can hold.
• list_unique() – Removes all duplicates of the consecutive elements from the list.
• emplace_front() – This function is used to insert a new element into the list and the element is added to the front of the list.
• emplace_back() – This function is used to insert a new element into the list and the element is added to the end of the list.
• clear() – Removes all the elements from the list and makes the size of the list 0
• swap() – This function is used to swap the contents of one list with another list of the same data type.
• splice() – Used to transfer elements from one list to another.
• merge() –  Used to merge two sorted lists into one.
• emplace(i) – Inserts a new element at a given position in the list.

Let’s look at an example of using a list.

// CPP program to show the implementation of List
#include <iostream>
#include <iterator>
#include <list>
using namespace std;
  
// function for printing the elements in a list
void showlist(list<int> g)
{
    list<int>::iterator it;
    for (it = g.begin(); it != g.end(); ++it)
        cout << '\t' << *it;
    cout << '\n';
}
  
// Driver Code
int main()
{
  
    list<int> gqlist1, gqlist2;
  
    for (int i = 0; i < 10; ++i) {
        gqlist1.push_back(i * 2);
        gqlist2.push_front(i * 3);
    }
    cout << "\nList 1 (gqlist1) is : ";
    showlist(gqlist1);
  
    cout << "\nList 2 (gqlist2) is : ";
    showlist(gqlist2);
  
    cout << "\ngqlist1.front() : " << gqlist1.front();
    cout << "\ngqlist1.back() : " << gqlist1.back();
  
    cout << "\ngqlist1.pop_front() : ";
    gqlist1.pop_front();
    showlist(gqlist1);
  
    cout << "\ngqlist2.pop_back() : ";
    gqlist2.pop_back();
    showlist(gqlist2);
  
    cout << "\ngqlist1.reverse() : ";
    gqlist1.reverse();
    showlist(gqlist1);
  
    cout << "\ngqlist2.sort(): ";
    gqlist2.sort();
    showlist(gqlist2);
  
    return 0;
}

Output:

List 1 (gqlist1) is :     0    2    4    6    8    10    12    14    16    18

List 2 (gqlist2) is :     27    24    21    18    15    12    9    6    3    0

gqlist1.front() : 0
gqlist1.back() : 18
gqlist1.pop_front() :     2    4    6    8    10    12    14    16    18

gqlist2.pop_back() :     27    24    21    18    15    12    9    6    3

gqlist1.reverse() :     18    16    14    12    10    8    6    4    2

gqlist2.sort():     3    6    9    12    15    18    21    24    27

That is all for this article. Happy Coding!