Skip site navigation (1)Skip section navigation (2)

FreeBSD Manual Pages

  
 
  

home | help 
std::uninitialized_copy_n(3)  C++ Standard Libary std::uninitialized_copy_n(3)

NAME
       std::uninitialized_copy_n - std::uninitialized_copy_n

Synopsis
	  Defined in header <memory>
	  template< class InputIt, class Size, class NoThrowForwardIt >
	  NoThrowForwardIt  uninitialized_copy_n(  InputIt  first, Size	count,
       (1) (since C++11)
	  NoThrowForwardIt d_first );
	  template< class ExecutionPolicy, class ForwardIt, class Size,
	  class	NoThrowForwardIt >

	  NoThrowForwardIt  uninitialized_copy_n(  ExecutionPolicy&&   policy,
       (2) (since C++17)
	  ForwardIt first, Size	count,

	  NoThrowForwardIt d_first );

	  1)  Copies  count  elements  from  a	range beginning	at first to an
       uninitialized memory
	  area beginning at d_first as if by

	for ( ;	n > 0; ++d_first, (void) ++first, --n)
	   ::new (/*VOIDIFY*/(*d_first))
	      typename			      std::iterator_traits<NoThrowFor-
       wardIt>::value_type(*first);

	  where	/*VOIDIFY*/(e) is:

	     static_cast<void*>(std::addressof(e))
       (until C++20)
	     const_cast<void*>(static_cast<const		      volatile
       (since C++20)
	     void*>(std::addressof(e)))

	  If an	exception is thrown during the initialization, the objects al-
       ready constructed
	  are destroyed	in an unspecified order.
	  2) Same as (1), but executed according to policy. This overload does
       not participate
	  in overload resolution unless
	  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)	is true.

Parameters
	  first		     -		the beginning of the range of the ele-
       ments to	copy
	  count		     -		the number of elements to copy
	  d_first	     -		the beginning of the destination range
	  policy	     -		the execution policy to	use. See  exe-
       cution policy for
					details.

Type requirements
	  -
	  InputIt must meet the	requirements of	LegacyInputIterator.
	  -
	  ForwardIt must meet the requirements of LegacyForwardIterator.
	  -
	  NoThrowForwardIt  must  meet the requirements	of LegacyForwardItera-
       tor.
	  -
	  No increment,	assignment, comparison,	or indirection	through	 valid
       instances of
	  NoThrowForwardIt may throw exceptions.

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
       errors 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::termi-
       nate is called.
	      For any other ExecutionPolicy, the behavior  is  implementation-
       defined.
	    *  If  the	algorithm  fails to allocate memory, std::bad_alloc is
       thrown.

Possible implementation
       template<class InputIt, class Size, class NoThrowForwardIt> NoThrowFor-
       wardIt uninitialized_copy_n(InputIt first, Size count, NoThrowForwardIt
       d_first)	{
	   using     T	   =	 typename     std::iterator_traits<NoThrowFor-
       wardIt>::value_type;
	   NoThrowForwardIt current = d_first;
	   try {
	       for (; count > 0; ++first, (void) ++current, --count) {
		   ::new (const_cast<void*>(static_cast<const volatile 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_tempo-
       rary_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::return_temporary_buffer(p);
	}

Output:
	This is	an example

See also
				       copies a	range of objects to an	unini-
       tialized	area of
	  uninitialized_copy	       memory
				       (function template)
	  ranges::uninitialized_copy_n copies a	number of objects to an	unini-
       tialized	area of
	  (C++20)		       memory
				       (niebloid)

http://cppreference.com		  2022.07.31	  std::uninitialized_copy_n(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=std::uninitialized_copy_n&sektion=3&manpath=FreeBSD+Ports+15.0>

home | help