std::ranges::uninitialized_move, std::ranges::uninitialized_move_result

 

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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 >     requires std::constructible_from<std::iter_value_t<O>,                                      std::iter_rvalue_reference_t<I>> uninitialized_move_result<I, O>     uninitialized_move( I ifirst, S1 ilast, O ofirst, S2 olast );	(1)	(since C++20) (constexpr since C++26)
template<ranges::input_range IR, no-throw-forward-range OR >     requires std::constructible_from                  <ranges::range_value_t<OR>,                   ranges::range_rvalue_reference_t<IR>> uninitialized_move_result<ranges::borrowed_iterator_t<IR>,                           ranges::borrowed_iterator_t<OR>>     uninitialized_move( IR&& in_range, OR&& out_range );	(2)	(since C++20) (constexpr since C++26)
Helper types
template<class I, class O > using uninitialized_move_result =ranges::in_out_result<I, O>;	(3)	(since C++20)

Let \(\scriptsize N\)N be ranges::min(ranges::distance(ifirst, ilast), ranges::distance(ofirst, olast)).

1) Copies \(\scriptsize N\)N elements from [ifirst, ilast) (using move semantics if supported) to an uninitialized memory area [ofirst, olast) as if by

for(; ifirst != ilast && ofirst != olast;++ofirst, (void)++ifirst)
    ::new(voidify(*ofirst))
        std::remove_reference_t<std::iter_reference_t<O>>(ranges::iter_move(ifirst));
return{std::move(ifirst), ofirst};

If an exception is thrown during the initialization then the objects that already constructed in [ofirst, olast) are destroyed in an unspecified order. Also, the objects in [ifirst, ilast) that were already moved, are left in a valid but unspecified state.

2) Equivalent to return ranges::uninitialized_move(ranges::begin(in_range), ranges::end(in_range),
                                  ranges::begin(out_range), ranges::end(out_range));.

The function-like entities described on this page are algorithm function objects (informally known as niebloids), that is:

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

Parameters

ifirst, ilast	-	the iterator-sentinel pair defining the input range of elements to move from
in_range	-	the input range of elements to move from
ofirst, olast	-	the iterator-sentinel pair defining the output range of elements to initialize
out_range	-	the output range to initialize

Return value

As described above.

Complexity

Linear in \(\scriptsize N\)N.

Exceptions

Any exception thrown on construction of the elements in the destination range.

Notes

An implementation may improve the efficiency of the ranges::uninitialized_move, e.g. by using ranges::copy_n, if the value type of the output range is TrivialType.

Feature-test macro	Value	Std	Feature
__cpp_lib_raw_memory_algorithms	202411L	(C++26)	constexpr for specialized memory algorithms, (1,2)

Possible implementation

struct uninitialized_move_fn {template<std::input_iterator I, std::sentinel_for<I> S1, no-throw-forward-iterator O, no-throw-sentinel-for<O> S2> requires std::constructible_from<std::iter_value_t<O>, std::iter_rvalue_reference_t<I>>constexpr ranges::uninitialized_move_result<I, O> operator()(I ifirst, S1 ilast, O ofirst, S2 olast)const{using ValueType =std::remove_reference_t<std::iter_reference_t<O>>; O current{ofirst};try{for(;!(ifirst == ilast or current == olast);++ifirst, ++current)::new(static_cast<void*>(std::addressof(*current)))) ValueType(ranges::iter_move(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> requires std::constructible_from<ranges::range_value_t<OR>, ranges::range_rvalue_reference_t<IR>>constexpr ranges::uninitialized_move_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_move_fn uninitialized_move{};

Example

Run this code

#include <cstdlib>#include <iomanip>#include <iostream>#include <memory>#include <string>   void print(auto rem, auto first, auto last){for(std::cout<< rem; first != last;++first)std::cout<<std::quoted(*first)<<' ';std::cout<<'\n';}   int main(){std::string in[]{"Home", "World"}; print("initially, in: ", std::begin(in), std::end(in));   if(constexprauto sz =std::size(in);void* out =std::aligned_alloc(alignof(std::string), sizeof(std::string)* sz)){try{auto first{static_cast<std::string*>(out)};auto last{first + sz}; std::ranges::uninitialized_move(std::begin(in), std::end(in), first, last);   print("after move, in: ", std::begin(in), std::end(in)); print("after move, out: ", first, last);   std::ranges::destroy(first, last);}catch(...){std::cout<<"Exception!\n";}std::free(out);}}

Possible output:

initially, in: "Home" "World" after move, in: "" "" after move, out: "Home" "World"

Defect reports

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 a const storage	kept disallowed

See also

ranges::uninitialized_move_n (C++20)	moves a number of objects to an uninitialized area of memory (algorithm function object)
uninitialized_move (C++17)	moves a range of objects to an uninitialized area of memory (function template)