std::list::erase(3)

🎀 std::list::erase 🎀

okay so this is the std::list::erase(3) page from the C++ Standard Libary manual — yes, “Libary” is literally what the header says, iykyk 😭 — and we’re about to make erasing list elements make sense. no cap 💅

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✨ NAME ✨

std::list::erase - std::list::erase

🧚 Synopsis 🧚

iterator erase( iterator pos );                          (until C++11)
iterator erase( const_iterator pos );                    (since C++11)
iterator erase( iterator first, iterator last );         (1) (until C++11)
iterator erase( const_iterator first,                    (2) (since C++11)
               const_iterator last );

Erases the specified elements from the container. ✨

1. Removes the element at pos.
2. Removes the elements in the range [first, last).

References and iterators to the erased elements are invalidated. Other references and iterators are not affected.

The iterator pos must be valid and dereferenceable. Thus the end() iterator (which is valid, but is not dereferenceable) cannot be used as a value for pos. 🫠

The iterator first does not need to be dereferenceable if first == last: erasing an empty range is a no-op. periodt.

🌸 Parameters 🌸

• pos — iterator to the element to remove.
• first, last — range of elements to remove.

🫶 Return value 🫶

Iterator following the last removed element.

1. If pos refers to the last element, then the end() iterator is returned.
2. If last == end() prior to removal, then the updated end() iterator is returned. If [first, last) is an empty range, then last is returned.

💀 Exceptions 💀

(none) — literally none listed, bestie. iconic.

⚡ Complexity ⚡

1. Constant.
2. Linear in the distance between first and last.

🧠 Notes 🧠

When container elements need to be erased based on a predicate, rather than iterating the container and calling unary erase, the iterator range overload is generally used with std::remove()/std::remove_if() to minimise the number of moves of the remaining (non-removed) elements, this is the erase-remove idiom. std::erase_if() replaces the erase-remove idiom. (since C++20)

🍓 Example 🍓

// Run this code

#include <list>
#include <iostream>
#include <iterator>

void print_container(const std::list<int>& c)
{
    for (int i : c)
        std::cout << i << ' ';
    std::cout << '\n';
}

int main()
{
    std::list<int> c{0, 1, 2, 3, 4, 5, 6, 7, 8, 9};
    print_container(c);

    c.erase(c.begin());
    print_container(c);

    std::list<int>::iterator range_begin = c.begin();
    std::list<int>::iterator range_end = c.begin();
    std::advance(range_begin, 2);
    std::advance(range_end, 5);

    c.erase(range_begin, range_end);
    print_container(c);

    // Erase all even numbers
    for (std::list<int>::iterator it = c.begin(); it != c.end();)
    {
        if (*it % 2 == 0)
            it = c.erase(it);
        else
            ++it;
    }
    print_container(c);
}

📤 Output 📤

0 1 2 3 4 5 6 7 8 9
1 2 3 4 5 6 7 8 9
1 2 6 7 8 9
1 7 9

🩹 Defect reports 🩹

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

• DR LWG 151, applied to C++98 — Behavior as published: first was required to be dereferenceable, which made the behavior of clearing an empty list undefined. Correct behavior: not required if first == last.

👀 See also 👀

• erase(std::list) — erases all elements satisfying specific criteria.
• erase_if(std::list) — (function template) (C++20).
• clear — clears the contents (public member function).

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mwah 💋 this page came from http://cppreference.com, dated 2024.06.10, and it’s the std::list::erase(3) page. bye bestie 🦋💖