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Defined in header <memory> | ||
Call signature | ||
template<std::input_iterator I, no-throw-forward-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_move_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 (using move semantics if supported) to an uninitialized memory area[ofirst, olast) as if byauto ret=ranges::uninitialized_move(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 then the objects that already constructed in[ofirst, olast) are destroyed in an unspecified order. Also, the objects in the input range beginning atifirst, that were already moved, are left in a valid but unspecified state.
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 the input range of elements to move from |
| ofirst, olast | - | the iterator-sentinel pair defining the outputrange of elements to initialize |
| n | - | the number of elements to move |
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_move_n, 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) |
struct uninitialized_move_n_fn{template<std::input_iterator I,no-throw-forward-iterator O, no-throw-sentinel-for<O> S> requiresstd::constructible_from<std::iter_value_t<O>,std::iter_rvalue_reference_t<I>>constexpr ranges::uninitialized_move_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_move(iter,std::default_sentinel, ofirst, olast);return{std::move(ret.in).base(), ret.out};}}; inlineconstexpr uninitialized_move_n_fn uninitialized_move_n{}; |
#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[]{"No","Diagnostic","Required",}; 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_n(std::begin(in), sz, 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: "No" "Diagnostic" "Required"after move, in: "" "" ""after move, out: "No" "Diagnostic" "Required"
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 range of objects to an uninitialized area of memory (algorithm function object)[edit] |
(C++17) | moves a number of objects to an uninitialized area of memory (function template)[edit] |
