std::ranges::destroy_n

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ranges::uninitialized_default_construct_n (C++20)
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ranges::destroy_n (C++20)
ranges::destroy_at (C++20)

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Defined in header`<memory>`
Call signature
template<no-throw-input-iterator I> requiresstd::destructible<std::iter_value_t<I>> constexpr I destroy_n( I first,std::iter_difference_t<I> n)noexcept;		(since C++20)

Destroys then objects in the range starting atfirst, equivalent to

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

The function-like entities described on this page arealgorithm function objects (informally known asniebloids), that is:

Explicit template argument lists cannot be specified when calling any of them.
None of them are visible toargument-dependent lookup.
When any of them are found bynormal unqualified lookup as the name to the left of the function-call operator,argument-dependent lookup is inhibited.

[edit]Parameters

first	-	the beginning of the range of elements to destroy
n	-	the number of elements to destroy

[edit]Return value

The end of the range of objects that has been destroyed.

[edit]Complexity

Linear inn.

[edit]Possible implementation

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

[edit]Example

The following example demonstrates how to useranges::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)unsignedchar 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::ranges::destroy_n(ptr,8);}

Output:

0 destructed1 destructed2 destructed3 destructed4 destructed5 destructed6 destructed7 destructed

[edit]See also

ranges::destroy_at (C++20)	destroys an object at a given address (algorithm function object)[edit]
ranges::destroy (C++20)	destroys a range of objects (algorithm function object)[edit]
destroy_n (C++17)	destroys a number of objects in a range (function template)[edit]