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std::uninitialized_fill_n(3)   C++ Standard Libary  std::uninitialized_fill_n(3)

NAME
     std::uninitialized_fill_n - std::uninitialized_fill_n

Synopsis
	Defined in header <memory>
	template< class ForwardIt, class Size, class T >
	ForwardIt uninitialized_fill_n( ForwardIt first, Size count, const (1)
	T& value );
	template< class ExecutionPolicy, class ForwardIt, class Size,
	class T >

	ForwardIt  uninitialized_fill_n(  ExecutionPolicy&& policy,	     (2)
     (since C++17)

					ForwardIt first, Size count, const
	T& value );

	1) Copies the given value value to the first count elements in an unini-
     tialized
	memory area beginning at first as if by for (; n--; ++first)
	    ::new (/* VOIDIFY */(*first))
		typename std::iterator_traits<ForwardIt>::value_type(value);
	where /* VOIDIFY */(e) is:

	static_cast<void*>(&e)		      (until C++11)
	static_cast<void*>(std::addressof(e)) (since C++11)

	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 partici-
     pates in
	overload resolution only if

	std::is_execution_policy_v<std::decay_t<ExecutionPolicy>>    is    true.
     (until
										  C++20)
	std::is_execution_policy_v<std::remove_cvref_t<ExecutionPolicy>>      is
     true. (since
										  C++20)

Parameters
	first		 -	     the beginning of the range of the	elements
     to
				     initialize
	count		 -	     number of elements to construct
	value		 -	     the value to construct the elements with

Type requirements
	-
	ForwardIt must meet the requirements of LegacyForwardIterator.
	-
	No  increment,	assignment, comparison, or indirection through valid in-
     stances of
	ForwardIt may throw exceptions.
	Applying &* to a ForwardIt value must yield a pointer to its value type.
	(until C++11)

Return value
	Iterator to the element past the last element copied.

Complexity
	Linear in count.

Exceptions
	The overload with a template parameter named ExecutionPolicy reports er-
     rors as
	follows:

	  * If execution of a function invoked as part of the  algorithm  throws
     an exception
	    and  ExecutionPolicy is one of the standard policies, std::terminate
     is called.
	    For any other ExecutionPolicy, the	behavior  is  implementation-de-
     fined.
	  * If the algorithm fails to allocate memory, std::bad_alloc is thrown.

Possible implementation
	template<class ForwardIt, class Size, class T>
	ForwardIt  uninitialized_fill_n(ForwardIt  first,  Size  count, const T&
     value)
	{
	    using V = typename std::iterator_traits<ForwardIt>::value_type;
	    ForwardIt current = first;
	    try
	    {
		for (; count > 0; ++current, (void) --count)
		    ::new	  (static_cast<void*>(std::addressof(*current)))
     V(value);
		return current;
	    }
	    catch (...)
	    {
		for (; first != current; ++first)
		    first->~V();
		throw;
	    }
	}

Example
     // Run this code

      #include <algorithm>
      #include <iostream>
      #include <memory>
      #include <string>
      #include <tuple>

      int main()
      {
	  std::string* p;
	  std::size_t sz;
	  std::tie(p, sz) = std::get_temporary_buffer<std::string>(4);
	  std::uninitialized_fill_n(p, sz, "Example");

	  for (std::string* i = p; i != p + sz; ++i)
	  {
	      std::cout << *i << '\n';
	      i->~basic_string<char>();
	  }
	  std::return_temporary_buffer(p);
      }

Output:
Example
Example
Example
Example
	Defect reports

	The  following	behavior-changing  defect  reports were applied retroac-
     tively to
	previously published C++ standards.

	   DR	 Applied to	     Behavior as published		 Correct
     behavior
			    given T as the value type of ForwardIt,
	LWG  866  C++98      if 				     uses global
     replacement-
			    T::operator new exists, the program     new instead
			    might be ill-formed
			    the location of the first element
	LWG 1339 C++98	    following				    returned
			    the filling range was not returned
	LWG 2433  C++11       this  algorithm  might  be  hijacked  by	    uses
     std::addressof
			    overloaded operator&
	LWG  3870 C++20      this algorithm might create objects on  kept disal-
     lowed
			    a const storage

See also
				     copies an object to an  uninitialized  area
     of memory,
	uninitialized_fill	     defined by a range
				     (function template)
	ranges::uninitialized_fill_n  copies  an object to an uninitialized area
     of memory,
	(C++20) 		     defined by a start and a count
				     (niebloid)

http://cppreference.com 	   2024.06.10	    std::uninitialized_fill_n(3)
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