std::ranges::destroy_n

 

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在标头 <memory> 定义
调用签名
template< no-throw-input-iterator I >     requires std::destructible<std::iter_value_t<I>> constexpr I destroy_n( I first, std::iter_difference_t<I> n ) noexcept;		(C++20 起)

销毁始于 first 的范围中的 n 个对象，等价于

return std::ranges::destroy(std::counted_iterator(first, n), std::default_sentinel).base();

此页面上描述的仿函数实体是 niebloid，即：

• 调用它们中的任何一个时不能显式指定模板实参。
• 它们都不对实参依赖查找可见。
• 在通过函数调用运算符左侧的名字进行无限定查找，找到它们之一时，禁止实参依赖查找。

实际上，它们能以函数对象，或者某些特殊编译器扩展实现。

参数

first	-	要销毁的元素范围的起始
n	-	要销毁的元素数

返回值

被销毁的元素的范围的末尾。

复杂度

与 n 成线性。

可能的实现

struct destroy_n_fn { template<no-throw-input-iterator I> requires std::destructible<std::iter_value_t<I>> constexpr I operator()(I first, std::iter_difference_t<I> n) const noexcept { for (; n != 0; (void)++first, --n) std::ranges::destroy_at(std::addressof(*first)); return first; } };   inline constexpr destroy_n_fn destroy_n{};

示例

下列示例演示如何用 ranges::destroy_n 销毁元素的相接序列。

运行此代码

#include <memory>
#include <new>
#include <iostream>
 
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}; // 手工构造对象
 
    auto ptr = std::launder(reinterpret_cast<Tracer*>(buffer));
 
    std::destroy_n(ptr, 8);
}

输出：

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

参阅

ranges::destroy_at (C++20)	销毁位于给定地址的元素 (niebloid)
ranges::destroy (C++20)	销毁范围中的元素 (niebloid)
destroy_n (C++17)	销毁范围中一定数量的对象 (函数模板)