std::destroy_n(3)

💅 std::destroy_n(3) — C++ Standard Library 💅

okay so bestie, welcome to the std::destroy_n page from the C++ Standard Library. It’s giving “clean up your objects” energy, and honestly? iconic. Let’s get into it. 🫶

---

🌸 NAME 🌸

std::destroy_n — literally std::destroy_n. That’s the name, bestie. 💖

---

🧚 Synopsis 🧚

It lives in the header <memory>, periodt. ✨

template< class ForwardIt, class Size >
ForwardIt destroy_n( ForwardIt first, Size n );            // since C++17, until C++20

template< class ForwardIt, class Size >
constexpr ForwardIt destroy_n( ForwardIt first, Size n );  // (1) since C++20

template< class ExecutionPolicy, class ForwardIt, class Size >
ForwardIt destroy_n( ExecutionPolicy&& policy, ForwardIt first, Size n );  // (2) since C++17

1. Destroys the n objects in the range starting at first, as if by:

for (; n > 0; (void) ++first, --n)
    std::destroy_at(std::addressof(*first));

2. Same as (1), but executed according to policy. This overload participates in overload resolution only if:

std::is_execution_policy_v<std::decay_t<ExecutionPolicy>> is true.        // (until C++20)
std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>> is true. // (since C++20)

---

🎀 Parameters 🎀

• first — the beginning of the range of elements to destroy.
• n — the number of elements to destroy.
• policy — the execution policy to use. See execution policy for details.

---

🦋 Type requirements 🦋

• ForwardIt must meet the requirements of LegacyForwardIterator.
• No increment, assignment, comparison, or indirection through valid instances of ForwardIt may throw exceptions.

bestie, those type requirements are not a vibe check you can skip 💀

---

⭐ Return value ⭐

The end of the range of objects that has been destroyed (i.e., std::next(first, n)).

---

🔥 Complexity 🔥

Linear in n.

---

🌈 Exceptions 🌈

The overload with a template parameter named ExecutionPolicy reports errors as follows:

• If execution of a function invoked as part of the algorithm throws an exception and ExecutionPolicy is one of the standard policies, std::terminate is called. For any other ExecutionPolicy, the behavior is implementation-defined.
• If the algorithm fails to allocate memory, std::bad_alloc is thrown.

---

👑 Possible implementation 👑

template<class ForwardIt, class Size>
constexpr // since C++20
ForwardIt destroy_n(ForwardIt first, Size n)
{
    for (; n > 0; (void) ++first, --n)
        std::destroy_at(std::addressof(*first));
    return first;
}

---

🍓 Example 🍓

The following example demonstrates how to use destroy_n to destroy a contiguous sequence of elements.

// Run this code

#include <iostream>
#include <memory>
#include <new>

struct Tracer
{
    int value;
    ~Tracer() { std::cout << value << " destructed\n"; }
};

int main()
{
    alignas(Tracer) unsigned char buffer[sizeof(Tracer) * 8];

    for (int i = 0; i < 8; ++i)
        new(buffer + sizeof(Tracer) * i) Tracer{i}; //manually construct objects

    auto ptr = std::launder(reinterpret_cast<Tracer*>(buffer));

    std::destroy_n(ptr, 8);
}

---

🎬 Output 🎬

0 destructed
1 destructed
2 destructed
3 destructed
4 destructed
5 destructed
6 destructed
7 destructed

---

🌟 See also 🌟

• destroy — destroys a range of objects; (C++17) (function template)
• destroy_at — destroys an object at a given address; (C++17) (function template)
• ranges::destroy_n — destroys a number of objects in a range; (C++20) (niebloid)

---

— xoxo, your Unix bestie 💖 source: http://cppreference.com · version/date: 2024.06.10 · page: std::destroy_n(3) 🫶