C++ std::list::begin

The std::list::begin function returns an iterator pointing to the first element of a std::list. This allows traversal of the list from the beginning using iterators. If the list is empty, the returned iterator is equal to end().

Syntax of std::list::begin

</>
Copy
iterator begin() noexcept;
const_iterator begin() const noexcept;

Parameters

The std::list::begin function does not take any parameters.

Return Value

Returns an iterator (or a constant iterator for const lists) pointing to the first element of the list. If the list is empty, the returned iterator is equal to std::list::end.

Exceptions

The std::list::begin function does not throw exceptions as it is marked noexcept.

Examples for std::list::begin

Example 1: Traversing a List Using std::list::begin

This example demonstrates iterating through the elements of a std::list using begin() and end():

</>
Copy
#include <iostream>
#include <list>

int main() {
    std::list<int> myList = {10, 20, 30, 40, 50};

    std::cout << "List elements: ";
    for (auto it = myList.begin(); it != myList.end(); ++it) {
        std::cout << *it << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation:

  1. Define a list: A std::list named myList is initialized with the elements {10, 20, 30, 40, 50}.
  2. Iterate using iterators: The program uses a for loop to iterate through the elements of the list using iterators:
    • myList.begin() returns an iterator pointing to the first element of the list.
    • myList.end() returns an iterator pointing to one past the last element of the list.
    • During each iteration, the dereference operator (*it) accesses the value of the element at the current iterator position.
  3. Access elements: All the elements of the list are printed in sequence, separated by spaces.

Output:

List elements: 10 20 30 40 50

Example 2: Modifying Elements Using std::list::begin

This example demonstrates how to modify elements of a std::list using begin():

</>
Copy
#include <iostream>
#include <list>

int main() {
    std::list<int> myList = {1, 2, 3, 4, 5};

    auto it = myList.begin(); // Get an iterator to the first element
    *it = 10; // Modify the first element

    std::cout << "Modified list: ";
    for (const auto& elem : myList) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation:

  1. Define a list: A std::list named myList is initialized with elements {1, 2, 3, 4, 5}.
  2. Get an iterator: The begin() function provides an iterator pointing to the first element of the list.
  3. Modify the element: The first element is modified by dereferencing the iterator and assigning a new value (10).
  4. Output the modified list: The updated list is printed using a range-based for loop.

Output:

Modified list: 10 2 3 4 5