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Difference between revisions of "cpp/memory/uninitialized copy n"

From cppreference.com
< cpp‎ | memory
(s/result/d_first/)
(LWG2133)
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Copies {{tt|count}} elements from a range beginning at {{tt|first}} to an uninitialized memory area beginning at {{tt|d_first}} as if by
 
Copies {{tt|count}} elements from a range beginning at {{tt|first}} to an uninitialized memory area beginning at {{tt|d_first}} as if by
 
{{source|1=
 
{{source|1=
−
for ( ; n > 0; ++d_first, ++first, --n)
+
for ( ; n > 0; ++d_first, (void) ++first, --n)
 
   ::new (static_cast<void*>(std::addressof(*d_first)))
 
   ::new (static_cast<void*>(std::addressof(*d_first)))
 
       typename iterator_traits<ForwardIterator>::value_type(*first);
 
       typename iterator_traits<ForwardIterator>::value_type(*first);
Line 38: Line 38:
 
     ForwardIt current = d_first;
 
     ForwardIt current = d_first;
 
     try {
 
     try {
−
         for (; count > 0; ++first, ++current, --count) {
+
         for (; count > 0; ++first, (void) ++current, --count) {
 
             ::new (static_cast<void*>(std::addressof(*current))) Value(*first);
 
             ::new (static_cast<void*>(std::addressof(*current))) Value(*first);
 
         }
 
         }

Revision as of 02:01, 27 October 2015

 
C++
 
Utilities library
General utilities
Relational operators (deprecated in C++20)
 
Dynamic memory management
Uninitialized memory algorithms
Constrained uninitialized memory algorithms
Allocators
Garbage collection support
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)
(C++11)(until C++23)



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

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 (static_cast<void*>(std::addressof(*d_first)))
      typename iterator_traits<ForwardIterator>::value_type(*first);

If an exception is thrown during the initialization, the function has no effects.

Contents

Parameters

first - the beginning of the range of the elements to copy
d_first - the beginning of the destination range
Type requirements

Template:par req concept Template:par req concept

Return value

Iterator to the element past the last element copied.

Complexity

Linear in count.

Possible implementation

template<class InputIt, class Size, class ForwardIt>
ForwardIt uninitialized_copy_n(InputIt first, Size count, ForwardIt d_first)
{
    typedef typename std::iterator_traits<ForwardIt>::value_type Value;
    ForwardIt current = d_first;
    try {
        for (; count > 0; ++first, (void) ++current, --count) {
            ::new (static_cast<void*>(std::addressof(*current))) Value(*first);
        }
    } catch (...) {
        for (; d_first != current; ++d_first) {
            d_first->~Value();
        }
        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::return_temporary_buffer(p);
}

Output: 

This is an example

See also

 copies a range of objects to an uninitialized area of memory
(function template) [edit]
(parallelism TS)
 parallelized version of std::uninitialized_copy_n
(function template) [edit]
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