C++ std::list::remove

C++ std::list::remove

The std::list::remove function removes all elements in a std::list that are equal to a specified value. This function is particularly useful for filtering out elements from the list. It performs the operation in linear time, traversing the list and removing all matching elements.

---

Syntax of std::list::remove

void remove(const value_type& val);

Parameters

Parameter	Description
val	The value of the elements to be removed from the list. All elements equal to this value will be removed.

Return Value

This function does not return a value. It modifies the list by removing all matching elements.

Exceptions

The std::list::remove function does not throw exceptions. It provides a no-throw guarantee since it only involves traversing the list and modifying internal pointers.

---

Examples for std::list::remove

Example 1: Removing a Single Value

This example demonstrates how to use remove to eliminate all occurrences of a specific value from the list:

Program

#include <iostream>
#include <list>

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

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

    // Remove all occurrences of the value 20
    myList.remove(20);

    std::cout << "List contents after remove: ";
    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, 20, 40}.
2. The remove function is called with the value 20. All occurrences of this value are removed from the list.
3. The modified contents of myList are printed, showing that the value 20 has been removed.

Output:

List contents before remove: 10 20 30 20 40
List contents after remove: 10 30 40

Example 2: Removing Elements from an Empty List

This example demonstrates that calling remove on an empty list does nothing:

Program

#include <iostream>
#include <list>

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

    // Try to remove a value from an empty list
    myList.remove(10);

    std::cout << "List size after remove on an empty list: " << myList.size() << std::endl;

    return 0;
}

Explanation:

1. A std::list named myList is created and is initially empty.
2. The remove function is called with the value 10, but since the list is empty, nothing happens.
3. The size() function is used to confirm that the list remains empty after the operation.

Output:

List size after remove on an empty list: 0

Example 3: Removing Elements from a List of Strings

This example demonstrates how remove works with a std::list containing strings:

Program

#include <iostream>
#include <list>
#include <string>

int main() {
    std::list<std::string> myList = {"apple", "banana", "apple", "cherry"};

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

    // Remove all occurrences of "apple"
    myList.remove("apple");

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

    return 0;
}

Explanation:

1. A std::list of strings named myList is initialized with {"apple", "banana", "apple", "cherry"}.
2. The remove function is called with the value "apple". All occurrences of this value are removed from the list.
3. The modified contents of myList are printed, showing that "apple" has been removed.

Output:

List contents before remove: apple banana apple cherry
List contents after remove: banana cherry