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    std::uninitialized_copy_n

    From cppreference.com
     
    C++
     
    Algorithm library
    Constrained algorithms and algorithms on ranges (C++20)
    Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
    Non-modifying sequence operations    
    Batch operations
    (C++17)
    Search operations
    Modifying sequence operations
    Copy operations
    (C++11)
    (C++11)
    (C++11)
    Swap operations
    Transformation operations
    Generation operations
    Removing operations
    Order-changing operations
    (until C++17)(C++11)
    (C++20)(C++20)
    Sampling operations
    (C++17)

    Sorting and related operations
    Partitioning operations
    (C++11)    
    (C++11)

    Sorting operations
    Binary search operations
    (on partitioned ranges)
    Set operations (on sorted ranges)
    Merge operations (on sorted ranges)
    Heap operations
    Minimum/maximum operations
    (C++11)
    (C++17)
    Lexicographical comparison operations
    (C++20)
    Permutation operations


     
    Specialized <memory> algorithms
    Helper templates (exposition only*)
    (C++17)
    Object (batch) construction
    Object (batch) destruction
    (C++17)
    (C++17)
    (C++17)
     
    Defined in header <memory> 
    template< class InputIt, class Size, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_copy_n( InputIt first, Size count,
                                       NoThrowForwardIt d_first );
    		(1) (since C++11)
    (constexpr since C++26)    		 
    template< class ExecutionPolicy, class ForwardIt,
          class Size, class NoThrowForwardIt >
NoThrowForwardIt uninitialized_copy_n( ExecutionPolicy&& policy,
                                       ForwardIt first, Size count,
                                       NoThrowForwardIt d_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 (voidify(*d_first))
            typename std::iterator_traits<NoThrowForwardIt>::value_type(*first);
    return d_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 execution policy to use
    Type requirements
    -
    InputIt must meet the requirements of LegacyInputIterator.
    -
    ForwardIt must meet the requirements of LegacyForwardIterator.
    -
    NoThrowForwardIt must meet the requirements of LegacyForwardIterator.
    -
    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, std::bad_alloc is thrown.
    • If an uncaught exception is thrown while accessing objects via an algorithm argument, the behavior is determined by the execution policy (for standard policies, std::terminate is invoked).

    Notes

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

    Possible implementation

    template<class InputIt, class Size, class NoThrowForwardIt>
constexpr NoThrowForwardIt uninitialized_copy_n(InputIt first, Size count,
                                                NoThrowForwardIt d_first)
{
    using T = typename std::iterator_traits<NoThrowForwardIt>::value_type;
    NoThrowForwardIt current = 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;
    }
    return current;
}

    Example

    Run this code
    #include <algorithm>
#include <iostream>
#include <memory>
#include <string>
#include <tuple>
#include <vector>

int main()
{
    std::vector<std::string> v = {"This", "is", "an", "example"};
    
    std::string* p;
    std::size_t sz;
    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
    LWG 2133 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
    LWG 2433 C++11 this algorithm might be hijacked by overloaded operator& uses std::addressof

    See also

    		 copies a range of objects to an uninitialized area of memory
    (function template & algorithm function object)[edit]
    (C++20)
    (C++20)
    		 copies a number of objects to an uninitialized area of memory
    (algorithm function object)[edit]