|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Defined in header <memory> | ||
Call signature | ||
template<std::input_iterator I,std::sentinel_for<I> S1, no-throw-forward-iterator O, no-throw-sentinel-for<O> S2> | (1) | (since C++20) (constexpr since C++26) |
template<ranges::input_range IR,no-throw-forward-range OR> requiresstd::constructible_from<ranges::range_value_t<OR>, | (2) | (since C++20) (constexpr since C++26) |
Helper types | ||
template<class I,class O> using uninitialized_copy_result=ranges::in_out_result<I, O>; | (3) | (since C++20) |
Let\(\scriptsize N\)N beranges::min(ranges::distance(ifirst, ilast),ranges::distance(ofirst, olast)).
[ifirst, ilast) to an uninitialized memory area[ofirst, olast) as if byfor(; ifirst!= ilast&& ofirst!= olast;++ofirst,(void)++ifirst) ::new(voidify(*ofirst))std::remove_reference_t<std::iter_reference_t<O>>(*ifirst);
return{std::move(ifirst), ofirst};
[ofirst, olast) overlaps with[ifirst, ilast), the behavior is undefined.The function-like entities described on this page arealgorithm function objects (informally known asniebloids), that is:
Contents |
| ifirst, ilast | - | the iterator-sentinel pair defining the sourcerange of elements to copy from |
| in_range | - | therange of elements to copy from |
| ofirst, olast | - | the iterator-sentinel pair defining the destinationrange of elements |
| out_range | - | the destinationrange |
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 ofranges::uninitialized_copy 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,(1,2) |
struct uninitialized_copy_fn{template<std::input_iterator I,std::sentinel_for<I> S1,no-throw-forward-iterator O, no-throw-sentinel-for<O> S2> requiresstd::constructible_from<std::iter_value_t<O>,std::iter_reference_t<I>>constexpr ranges::uninitialized_copy_result<I, O> operator()(I ifirst, S1 ilast, O ofirst, S2 olast)const{ O current{ofirst};try{for(;!(ifirst== ilast or current== olast);++ifirst,++current)ranges::construct_at(std::addressof(*current),*ifirst);return{std::move(ifirst), std::move(current)};}catch(...)// rollback: destroy constructed elements{for(; ofirst!= current;++ofirst)ranges::destroy_at(std::addressof(*ofirst));throw;}} template<ranges::input_range IR,no-throw-forward-range OR> requiresstd::constructible_from<ranges::range_value_t<OR>,constexprranges::range_reference_t<IR>> ranges::uninitialized_copy_result<ranges::borrowed_iterator_t<IR>,ranges::borrowed_iterator_t<OR>> operator()(IR&& in_range, OR&& out_range)const{return(*this)(ranges::begin(in_range),ranges::end(in_range),ranges::begin(out_range),ranges::end(out_range));}}; inlineconstexpr uninitialized_copy_fn uninitialized_copy{}; |
#include <cstdlib>#include <iomanip>#include <iostream>#include <memory>#include <string> int main(){constchar* v[]{"This","is","an","example"}; if(constauto sz{std::size(v)};void* pbuf=std::aligned_alloc(alignof(std::string), sizeof(std::string)* sz)){try{auto first{static_cast<std::string*>(pbuf)};auto last{first+ sz}; std::ranges::uninitialized_copy(std::begin(v),std::end(v), first, last); std::cout<<"{";for(auto it{first}; it!= last;++it)std::cout<<(it== first?"":", ")<<std::quoted(*it);std::cout<<"};\n"; std::ranges::destroy(first, last);}catch(...){std::cout<<"uninitialized_copy exception\n";}std::free(pbuf);}}
Output:
{"This", "is", "an", "example"};The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
| DR | Applied to | Behavior as published | Correct behavior |
|---|---|---|---|
| LWG 3870 | C++20 | this algorithm might create objects on aconst storage | kept disallowed |
(C++20) | copies a number of objects to an uninitialized area of memory (algorithm function object)[edit] |
| copies a range of objects to an uninitialized area of memory (function template)[edit] |
