list front() function in C++ STL

The list::front() is a built-in function in C++ STL which is used to return a reference to the first element in a list container. Unlike the list::begin() function, this function returns a direct reference to the first element in the list container. Syntax: 

list_name.front() 

Parameters: This function does not accept any parameter, it simply returns a reference to the first element in the list container. Return Value: This function returns a direct reference to the first element in the list container. Exception: This function creates an undefined behavior when used with an empty list container. Below program illustrates the list::front() function. 

CPP

// CPP program to illustrate the
// list::front() function
#include <bits/stdc++.h>
using namespace std;

int main()
{
    // Creating a list
    list<int> demoList;

    // Add elements to the List
    demoList.push_back(10);
    demoList.push_back(20);
    demoList.push_back(30);
    demoList.push_back(40);

    // get the first element using front()
    int ele = demoList.front();

    // Print the first element
    cout << ele;

    return 0;
}

Output:

10

Note: This function works in constant time complexity.

Time complexity: O(1)

Auxiliary Space: O(n) where n is size of the list

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