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Defined in header <memory> | ||
Call signature | ||
template<std::input_iterator I, no-throw-input-iterator O, no-throw-sentinel-for<O> S> | (1) | (since C++20) (constexpr since C++26) |
Helper types | ||
template<class I,class O> using uninitialized_copy_n_result=ranges::in_out_result<I, O>; | (2) | (since C++20) |
Let\(\scriptsize N\)N beranges::min(count,ranges::distance(ofirst, olast)).
Copies\(\scriptsize N\)N elements from the range beginning atifirst to an uninitialized memory area[ofirst, olast) as if byauto ret=ranges::uninitialized_copy(std::counted_iterator(std::move(ifirst), count),
std::default_sentinel, ofirst, olast);
return{std::move(ret.in).base(), ret.out};
If an exception is thrown during the initialization, the objects already constructed are destroyed in an unspecified order.
If[ofirst, olast) overlaps withifirst + [0, count), the behavior is undefined.
The function-like entities described on this page arealgorithm function objects (informally known asniebloids), that is:
Contents |
| ifirst | - | the beginning of therange of elements to copy from |
| count | - | the number of elements to copy |
| ofirst, olast | - | the iterator-sentinel pair defining the destinationrange of elements |
As described above.
\(\scriptsize\mathcal{O}(N)\)𝓞(N).
Any exception thrown on construction of the elements in the destination range.
An implementation may improve the efficiency of theranges::uninitialized_copy_n, by using e.g.ranges::copy_n, if the value type of the output range isTrivialType.
| Feature-test macro | Value | Std | Feature |
|---|---|---|---|
__cpp_lib_raw_memory_algorithms | 202411L | (C++26) | constexpr forspecialized memory algorithms,(1) |
struct uninitialized_copy_n_fn{template<std::input_iterator I,no-throw-input-iterator O, no-throw-sentinel-for<O> S> requiresstd::constructible_from<std::iter_value_t<O>,std::iter_reference_t<I>>constexpr ranges::uninitialized_copy_n_result<I, O> operator()(I ifirst,std::iter_difference_t<I> count, O ofirst, S olast)const{auto iter=std::counted_iterator(std::move(ifirst), count);auto ret=ranges::uninitialized_copy(iter,std::default_sentinel, ofirst, olast);return{std::move(ret.in).base(), ret.out};}}; inlineconstexpr uninitialized_copy_n_fn uninitialized_copy_n{}; |
#include <iomanip>#include <iostream>#include <memory>#include <string> int main(){constchar* stars[]{"Procyon","Spica","Pollux","Deneb","Polaris"}; constexprint n{4}; alignas(alignof(std::string))char out[n* sizeof(std::string)]; try{auto first{reinterpret_cast<std::string*>(out)};auto last{first+ n};auto ret{std::ranges::uninitialized_copy_n(std::begin(stars), n, first, last)}; std::cout<<'{';for(auto it{first}; it!= ret.out;++it)std::cout<<(it== first?"":", ")<<std::quoted(*it);std::cout<<"};\n"; std::ranges::destroy(first, last);}catch(...){std::cout<<"uninitialized_copy_n exception\n";}}
Output:
{"Procyon", "Spica", "Pollux", "Deneb"};(C++20) | copies a range of objects to an uninitialized area of memory (algorithm function object)[edit] |
(C++11) | copies a number of objects to an uninitialized area of memory (function template)[edit] |
