From cppreference.com
Defined in header
template<classInputIt,classSize,classNoThrowForwardIt>NoThrowForwardItuninitialized_copy_n(InputItfirst,Sizecount,NoThrowForwardItd_first); (1)(since C++11)
(constexpr since C++26)template<classExecutionPolicy,classForwardIt,classSize,classNoThrowForwardIt>NoThrowForwardItuninitialized_copy_n(ExecutionPolicy&&policy,ForwardItfirst,Sizecount,NoThrowForwardItd_first); (2) (since C++17)1) Constructs elements in the destination range beginning at d_first from the first count elements in the source range beginning at first as if by
for(;count>0;++d_first,(void)++first,--count)
::new(
(*d_first))
typenamestd::iterator_traits<NoThrowForwardIt>::value_type(*first);
returnd_first;
If an exception is thrown during the initialization, the objects already constructed are destroyed in an unspecified order.
2) Same as (1), but executed according to policy.
This overload participates in overload resolution only if the value of the following expression is true:
std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>
(until C++20)std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>
(since C++20)If d_first + [0, count) overlaps with first + [0, count), the behavior is undefined.
(since C++20)Parameters
first - the beginning of the range of the elements to copy count - the number of elements to copy d_first - the beginning of the target range policy - the
to use Type requirements -InputIt must meet the requirements of
. -ForwardIt must meet the requirements of
. -NoThrowForwardIt must meet the requirements of
. -No increment, assignment, comparison, or indirection through valid instances of NoThrowForwardIt may throw exceptions. Return value
As described above.
Exceptions
2) During the execution process:
If the temporary memory resources required for parallelization are not available,
is thrown.
If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for
,
is invoked).
Notes
macroValueStdFeature
__cpp_lib_raw_memory_algorithms
(C++26)constexpr for
specialized <memory> algorithms
, (
)Possible implementation
template<classInputIt,classSize,classNoThrowForwardIt>constexprNoThrowForwardItuninitialized_copy_n(InputItfirst,Sizecount,NoThrowForwardItd_first){usingT=typenamestd::iterator_traits<NoThrowForwardIt>::value_type;NoThrowForwardItcurrent=d_first;try{for(;count>0;++first,(void)++current,--count)::new(static_cast<void*>(std::addressof(*current)))T(*first);}catch(...){for(;d_first!=current;++d_first)d_first->~T();throw;}returncurrent;}Example
Run this code
#include<algorithm>#include<iostream>#include<memory>#include<string>#include<tuple>#include<vector>intmain(){std::vector<std::string>v={"This","is","an","example"};std::string*p;std::size_tsz;std::tie(p,sz)=std::get_temporary_buffer<std::string>(v.size());sz=std::min(sz,v.size());std::uninitialized_copy_n(v.begin(),sz,p);for(std::string*i=p;i!=p+sz;++i){std::cout<<*i<<' ';i->~basic_string<char>();}std::cout<<'\n';std::return_temporary_buffer(p);}Possible output:
This is an example Defect reports
The following behavior-changing defect reports were applied retroactively to previously published C++ standards.
DR Applied to Behavior as published Correct behavior
C++98 the effect description used a for loop with the iteration
expression ++d_first,++first,--count, which
results in argument-dependent lookups of operator,discards the value
of one operand to
disable those ADLs
C++11 this algorithm might be hijacked by overloaded operator&uses
See also