|
| |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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 | (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 beranges::min(ranges::distance(ifirst, ilast),ranges::distance(ofirst, olast)).
[ifirst, ilast) (using move semantics if supported) 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>>(ranges::iter_move(ifirst));
return{std::move(ifirst), ofirst};
[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.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 inputrange of elements to move from |
| in_range | - | the inputrange of elements to move from |
| ofirst, olast | - | the iterator-sentinel pair defining the outputrange of elements to initialize |
| out_range | - | the outputrange to initialize |
As described above.
Linear in\(\scriptsize N\)N.
Any exception thrown on construction of the elements in the destination range.
An implementation may improve the efficiency of theranges::uninitialized_move, e.g. by usingranges::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,(1,2) |
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> requiresstd::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> requiresstd::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{}; |
#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"
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) | moves a number of objects to an uninitialized area of memory (algorithm function object)[edit] |
(C++17) | moves a range of objects to an uninitialized area of memory (function template)[edit] |
