C++ std::list::pop_front

The std::list::pop_front function removes the first element from a std::list. This operation reduces the size of the list by one, but does not return the removed element. The function is commonly used when processing elements from the front of a list in FIFO (First In, First Out) operations.

Syntax of std::list::pop_front

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void pop_front();

Parameters

This function does not accept any parameters.

Return Value

The function does not return any value. It removes the first element of the list and adjusts the size accordingly.

Exceptions

The std::list::pop_front function does not throw exceptions itself. However, accessing the function on an empty list does not throw an exception, but calling it on an empty list results in undefined behavior.

To avoid undefined behavior, always ensure the list is not empty before calling pop_front. This can be done using the empty() method.

Examples for std::list::pop_front

Example 1: Removing Elements from the Front

This example demonstrates how to use pop_front to remove elements from the front of a list:

Program

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#include <iostream>
#include <list>

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

    myList.pop_front(); // Remove the first element (10)

    std::cout << "List contents after pop_front: ";
    for (const auto& elem : myList) {
        std::cout << elem << " ";
    }
    std::cout << std::endl;

    return 0;
}

Explanation:

  1. A std::list named myList is initialized with the elements {10, 20, 30, 40}.
  2. The pop_front function is called, removing the first element 10.
  3. The remaining elements of the list are printed using a range-based for loop.

Output:

List contents after pop_front: 20 30 40

Example 2: Handling Empty List

This example demonstrates how to safely call pop_front on a list and avoid undefined behavior:

Program

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#include <iostream>
#include <list>

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

    if (!myList.empty()) {
        myList.pop_front();
    } else {
        std::cout << "List is empty, cannot call pop_front." << std::endl;
    }

    return 0;
}

Explanation:

  1. A std::list named myList is created and is initially empty.
  2. The empty() method is used to check if the list contains elements before calling pop_front.
  3. If the list is empty, a message is printed to indicate that the operation cannot be performed.

Output:

List is empty, cannot call pop_front.