list resize() function in C++ STL

The list::resize() is a built-in function in C++ STL which is used to resize a list container. It takes a number n as parameter and resizes the list container to contain exactly n elements.

If the list already has more than n elements, then the function erases the elements from the list except the first n element.
If the list contains less than n elements, then the function adds the difference number of elements to the list with their default values.
The function also accepts a parameter val, if this parameter is specified and the number of elements in the list container is less than n then the function adds elements to the list with their value assigned to val.

Syntax:

list_name.resize(int n, value_type val)

Parameters: This function accepts two parameters as described below.

n : This parameter specifies the number of elements upto which the list is needed to be resized.
val: This is an optional parameter and if it is specified and the list contains less than n elements then the function will add elements to the list with their value assigned to val.

Return Value: This function does not return any value.

Below program illustrate the list::resize() function in C++ STL:

// CPP program to illustrate the 
// list::resize() function 
#include <bits/stdc++.h> 
using namespace std; 
  
int main() 
{ 
    // Creating a list 
    list<int> demoList; 
  
    // Adding elements to the list 
    demoList.push_back(10); 
    demoList.push_back(20); 
    demoList.push_back(30); 
    demoList.push_back(40); 
  
    // Initial list: 
    cout << "Initial List: "; 
    for (auto itr = demoList.begin(); itr != demoList.end(); itr++) 
        cout << *itr << " "; 
  
    // Resize list to contain less elements 
    demoList.resize(2); 
    cout << "\n\nList after first resize: "; 
    for (auto itr = demoList.begin(); itr != demoList.end(); itr++) 
        cout << *itr << " "; 
  
    // Resize list to contain more elements 
    demoList.resize(4); 
    cout << "\n\nList after second resize: "; 
    for (auto itr = demoList.begin(); itr != demoList.end(); itr++) 
        cout << *itr << " "; 
  
    // resize list to contain more elements 
    // with a specified value 
    demoList.resize(5, 50); 
    cout << "\n\nList after third resize: "; 
    for (auto itr = demoList.begin(); itr != demoList.end(); itr++) 
        cout << *itr << " "; 
  
    return 0; 
} 

Output:

Initial List: 10 20 30 40 

List after first resize: 10 20 

List after second resize: 10 20 0 0 

List after third resize: 10 20 0 0 50

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