C++ List

C++ List

A list is similar to a vector in that it can store multiple elements of the same type and dynamically grow in size.

However, two major differences between lists and vectors are:

1. You can add and remove elements from both the beginning and at the end of a list, while vectors are generally optimized for adding and removing at the end.
2. Unlike vectors, a list does not support random access, meaning you cannot directly jump to a specific index, or access elements by index numbers. Instead, you must traverse the list to reach a specific element.

To use a list, you have to include the <list> header file:

  // Include the list library
#include <list>

Create a List

To create a list, use the list keyword, and specify the type of values it should store within angle brackets <> and then the name of the list, like: list<type> listName.

Example

  // Create a list called cars that will store strings
list<string> cars;

If you want to add elements at the time of declaration, place them in a comma-separated list, inside curly braces {}:

Example

// Create a list called cars that will store strings
list<string> cars = {"Volvo", "BMW",
"Ford", "Mazda"};

// Print list elements
for (string car : cars) {
  cout << car << "\n";
}

Note: The type of the list (string in our example) cannot be changed after its been declared.

Access a List

You cannot access list elements by referring to index numbers, like with arrays and vectors.

However, you can access the first or the last element with the .front() and .back() functions, respectively:

Example

// Create a list called cars that will store strings
list<string> cars = {"Volvo", "BMW",
"Ford", "Mazda"};

// Get the first element
cout << cars.front();  // Outputs Volvo

// Get the
last element
cout << cars.back();  // Outputs Mazda

Change a List Element

You can also change the value of the first or the last element with the .front() and .back() functions

Example

list<string> cars = {"Volvo", "BMW", "Ford", "Mazda"};

// Change the
value of the first element
cars.front() = "Opel";

// Change the
value of the last element
cars.back() = "Toyota";

cout << cars.front(); // Now
outputs Opel instead of Volvo
cout << cars.back();  // Now
outputs Toyota instead of Mazda

Add List Elements

To add elements to a list, you can use .push_front() to insert an element at the beginning of the list and .push_back() to add an element at the end:

Example

  list<string> cars = {"Volvo", "BMW", "Ford", "Mazda"};

// Add an
  element at the beginning
cars.push_front("Tesla");

// Add an element
  at the end
cars.push_back("VW");

Remove List Elements

To remove elements from a list, use .pop_front() to remove an element from the beginning of the list and .pop_back() to remove an element at the end:

Example

  list<string> cars = {"Volvo", "BMW", "Ford", "Mazda"};

// Remove the
  first element
cars.pop_front();

// Remove the last element
cars.pop_back();

List Size

To find out how many elements a list has, use the .size() function:

Example

list<string> cars = {"Volvo", "BMW", "Ford", "Mazda"};
cout << cars.size();
// Outputs 4

Check if a List is Empty

Use the .empty() function to find out if a list is empty or not.

The .empty() function returns 1 (true) if the list is empty and 0 (false) otherwise:

Example

list<string> cars;
cout << cars.empty();
// Outputs 1 (The list is empty)

Example

list<string> cars = {"Volvo", "BMW", "Ford", "Mazda"};
cout << cars.empty();
// Outputs 0 (not empty)

Loop Through a List

You cannot loop through the list elements with a traditional for loop combined with the .size() function, since it is not possible to access elements in a list by index:

Example

list<string> cars = {"Volvo", "BMW", "Ford", "Mazda"};

for (int i =
0; i < cars.size(); i++) {
  cout << cars[i] << "\n";
}

The simplest way to loop through a list is with the for-each loop:

Example

list<string> cars = {"Volvo", "BMW", "Ford", "Mazda"};

for (string car : cars) {
  cout << car << "\n";
}

Tip: It is also possible to loop through lists with an iterator, which you will learn more about in a later chapter.