List in C++ Standard Template Library (STL)
Last Updated :
28 Feb, 2024
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Lists are sequence containers that allow non-contiguous memory allocation. As compared to the vector, the list has slow traversal, but once a position has been found, insertion and deletion are quick (constant time). Normally, when we say a List, we talk about a doubly linked list. For implementing a singly linked list, we use a forward_list.
std::list is the class of the List container. It is the part of C++ Standard Template Library (STL) and is defined inside <list> header file.
Syntax:
std::list <data-type> name_of_list;
Example:
C++
// C++ program to demonstrate the use of list containers#include <iostream>#include <list>using namespace std;int main(){ // defining list list<int> gqlist{12,45,8,6}; for (auto i : gqlist) { cout << i << ' '; } return 0;} |
Output
12 45 8 6
In the above example, we created a std::list object named gqlist and initialized it using an initializer_list. We can initialize the std::list objects using many different ways mentioned here.
Some Basic Operations on std::list
- front() – Returns the value of the first element in the list.
- back() – Returns the value of the last element in the list.
- push_front() – Adds a new element ‘g’ at the beginning of the list.
- push_back() – Adds a new element ‘g’ 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.
- insert() – Inserts new elements in the list before the element at a specified position.
- size() – Returns the number of elements in the list.
- begin() – begin() function returns an iterator pointing to the first element of the list.
- end() – end() function returns an iterator pointing to the theoretical last element which follows the last element.
The below example demonstrates the general use of list containers and their basic functions in C++.
Example:
C++
// C++ program to demonstrate the implementation of List#include <iostream>#include <iterator>#include <list>using namespace std;// function for printing the elements in a listvoid showlist(list<int> g){ list<int>::iterator it; for (it = g.begin(); it != g.end(); ++it) cout << '\t' << *it; cout << '\n';}// Driver Codeint 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
The above example only demonstrates the general usage of the std::list and its member functions. The below table provides all the member functions of std::list class and links to their detailed explanation.
std::list Member Functions
|
Functions |
Definition |
|---|---|
| front() | Returns the value of the first element in the list. |
| back() | Returns the value of the last element in the list. |
| push_front(g) | Adds a new element ‘g’ at the beginning of the list. |
| push_back(g) | Adds a new element ‘g’ 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::begin() | begin() function returns an iterator pointing to the first element of the list. |
| list::end() | end() function returns an iterator pointing to the theoretical last element which follows the last element. |
| list rbegin() and rend() | rbegin() returns a reverse iterator which points to the last element of the list. rend() returns a reverse iterator that points to the position before the beginning of the list. |
| list cbegin() and cend() | cbegin() returns a constant random access iterator which points to the beginning of the list. cend() returns a constant random access iterator which points to the end of the list. |
| list crbegin() and crend() | crbegin() returns a constant reverse iterator which points to the last element of the list i.e reversed beginning of the container. crend() returns a constant reverse iterator which points to the theoretical element preceding the first element in the list i.e. the reverse end of the list. |
| empty() | Returns whether the list is empty(1) or not(0). |
| insert() | Inserts new elements in the list before the element at a specified position. |
| erase() | Removes a single element or a range of elements from the list. |
| assign() | Assigns new elements to the list by replacing current elements and resizing the list. |
| remove() | Removes all the elements from the list, which are equal to a given element. |
| list::remove_if() | Used to remove all the values from the list that correspond true to the predicate or condition given as a parameter to the function. |
| reverse() | Reverses the list. |
| size() | Returns the number of elements in the list. |
| list resize() | Used to resize a list container. |
| sort() | Sorts the list in increasing order. |
| list max_size() | Returns the maximum number of elements a list container can hold. |
| list unique() | Removes all duplicate consecutive elements from the list. |
| list::emplace_front() and list::emplace_back() | .emplace_front() function is used to insert a new element into the list container and constructs the object in-place at the beginning of the list. . emplace_back() function is used to insert a new element into the list container,and constructs the object in-place at the end of the list. |
| list::clear() | clear() function is used to remove all the elements of the list container, thus making it size 0. |
| list::operator= | This operator is used to assign new contents to the container by replacing the existing contents. |
| list::swap() | This function is used to swap the contents of one list with another list. |
| list splice() | Used to transfer elements from one list to another. |
| list merge() | Merges two sorted lists into one. |
| list emplace() | Extends the list by inserting a new element at a given position and it constructs the object in-place at the beginning of the list, potentially improving performance by avoiding a copy operation |
Points to Remember about List Container
- It is generally implemented using a dynamic doubly linked list with traversal in both directions.
- Faster insert and delete operation as compared to arrays and vectors.
- It provides only sequential access. Random Access to any middle element is not possible
- It is defined as a template so it is able to hold any data type.
- It operates as an unsorted list would, which implies that by default, the list’s order is not preserved. However, there are techniques for sorting.
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