C++ std::list::back

The std::list::back function provides access to the last element of a std::list. This function returns a reference to the last element, allowing it to be read or modified.

Syntax of std::list::back

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reference back();
const_reference back() const;

Parameters

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

Return Value

Returns a reference to the last element in the list. If the list is const, the returned reference is also const, meaning the element cannot be modified.

Exceptions

The std::list::back function does not throw exceptions. However, calling this function on an empty list results in undefined behavior. It is recommended to check whether the list is empty using empty() before calling this function.

Examples for std::list::back

Example 1: Accessing the Last Element Using std::list::back

This example demonstrates how to use back() to access the last element of a list:

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#include <iostream>
#include <list>

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

    std::cout << "The last element is: " << myList.back() << std::endl;

    return 0;
}

Explanation:

  1. Define a list: A std::list named myList is initialized with elements {10, 20, 30}.
  2. Access the last element: The back() function is called on myList to retrieve the last element, which is 30.
  3. Print the element: The retrieved element is printed to the console.

Output:

The last element is: 30

Example 2: Modifying the Last Element Using std::list::back

This example demonstrates how to modify the last element of a list using back():

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#include <iostream>
#include <list>

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

    std::cout << "Before modification, last element: " << myList.back() << std::endl;

    myList.back() = 100; // Modify the last element

    std::cout << "After modification, last element: " << myList.back() << std::endl;

    return 0;
}

Explanation:

  1. Define a list: A std::list named myList is initialized with elements {1, 2, 3}.
  2. Access the last element: The back() function is called to retrieve the last element, which is 3.
  3. Modify the last element: The value of the last element is updated to 100 using myList.back() = 100.
  4. Print the modified element: The updated last element is printed to the console.

Output:

Before modification, last element: 3
After modification, last element: 100

Exception Handling in std::list::back

The std::list::back function does not throw exceptions. However, calling this function on an empty list results in undefined behavior. It is recommended to use the empty() function to check whether the list is empty before calling back().

Example 3: Avoiding Undefined Behavior with std::list::back

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#include <iostream>
#include <list>

int main() {
    std::list<int> emptyList;

    if (!emptyList.empty()) {
        std::cout << "Last element: " << emptyList.back() << std::endl;
    } else {
        std::cout << "The list is empty. No elements to access." << std::endl;
    }

    return 0;
}

Output:

The list is empty. No elements to access.