C++ std::list::remove_if

The std::list::remove_if function removes all elements from a std::list for which a specified predicate returns true. This allows you to filter elements from the list based on a custom condition. The function is particularly useful for removing elements that satisfy complex criteria.

Syntax of std::list::remove_if

</>

Copy

template <class Predicate>
void remove_if(Predicate pred);

Parameters

Parameter	Description
`pred`	A unary predicate function that returns `true` for elements that should be removed. The predicate should accept an element of the list as an argument.

Return Value

This function does not return a value. It modifies the list in place by removing elements that satisfy the predicate.

Exceptions

The std::list::remove_if function does not throw exceptions unless the predicate itself throws an exception. It provides strong exception safety: if an exception is thrown, the list remains unchanged.

Examples for std::list::remove_if

Example 1: Removing Odd Numbers

This example demonstrates how to use remove_if to remove all odd numbers from a list:

Program

</>

Copy

#include <iostream>
#include <list>

bool isOdd(int value) {
    return value % 2 != 0;
}

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

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

    // Remove all odd numbers
    myList.remove_if(isOdd);

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

    return 0;
}

Explanation:

A std::list named myList is initialized with the elements {1, 2, 3, 4, 5}.
A predicate function isOdd is defined to check if a number is odd.
The remove_if function is called with isOdd as the predicate, removing all odd numbers from the list.
The modified list contents are printed, showing that only the even numbers remain.

Output:

List contents before remove_if: 1 2 3 4 5
List contents after remove_if: 2 4

Example 2: Removing Strings with a Specific Condition

This example demonstrates how to use remove_if to remove strings with less than 5 characters:

Program

</>

Copy

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

bool isShort(const std::string& str) {
    return str.size() < 5;
}

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

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

    // Remove strings with less than 5 characters
    myList.remove_if(isShort);

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

    return 0;
}

Explanation:

A std::list of strings named myList is initialized with {"apple", "dog", "banana", "cat"}.
A predicate function isShort is defined to check if the length of a string is less than 5 characters.
The remove_if function is called with isShort as the predicate, removing all short strings from the list.
The modified list contents are printed, showing only the strings with 5 or more characters.

Output:

List contents before remove_if: apple dog banana cat
List contents after remove_if: apple banana

Example 3: Removing Elements Using a Lambda Expression

This example demonstrates how to use a lambda expression with remove_if to remove elements greater than a specified value:

Program

</>

Copy

#include <iostream>
#include <list>

int main() {
    std::list<int> myList = {1, 10, 20, 30, 5};

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

    // Remove elements greater than 15 using a lambda
    myList.remove_if([](int value) { return value > 15; });

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

    return 0;
}

Explanation:

A std::list named myList is initialized with {1, 10, 20, 30, 5}.
A lambda expression is used as the predicate to check if an element is greater than 15.
The remove_if function is called with the lambda expression, removing all elements greater than 15.
The modified list contents are printed, showing only elements less than or equal to 15.

Output:

List contents before remove_if: 1 10 20 30 5
List contents after remove_if: 1 10 5

TutorialKart

C++ std::list::remove_if