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

From cppreference.com
< cpp‎ | memory
m
(+ exception handling)
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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}}. The elements in the uninitialized area are constructed using copy constructor.
+
Copies {{tt|count}} elements from a range beginning at {{tt|first}} to an uninitialized memory area beginning at {{tt|d_first}}.
  
−
If an exception is thrown during the initialization, the function has no effects. {{todo|reason=update possible implementation to reflect this}}
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If an exception is thrown during the initialization, the function has no effects.  
  
 
===Parameters===
 
===Parameters===
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{
 
{
 
     typedef typename std::iterator_traits<ForwardIt>::value_type Value;
 
     typedef typename std::iterator_traits<ForwardIt>::value_type Value;
−
     for (; count > 0; ++first, ++d_first, --count) {
+
     ForwardIt current = d_first;
−
        ::new (static_cast<void*>(&*d_first)) Value(*first);
+
    try {
 +
        for (; count > 0; ++first, ++current, --count) {
 +
            ::new (static_cast<void*>(&*current)) Value(*first);
 +
        }
 +
    } catch (...) {
 +
        for (; d_first != current; ++d_first) {
 +
            d_first->~Value();
 +
        }
 +
        throw;
 
     }
 
     }
−
     return d_first;
+
     return current;
 
}
 
}
 
}}
 
}}

Revision as of 20:52, 2 May 2014

 
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.

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, ++current, --count) {
            ::new (static_cast<void*>(&*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]
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