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std::move

From cppreference.com
< cpp‎ | algorithm
Revision as of 13:38, 15 July 2013 by Cubbi (Talk | contribs)

 
 
 
Defined in header <algorithm>
template< class InputIt, class OutputIt >
OutputIt move( InputIt first, InputIt last, OutputIt d_first );
(since C++11)

Moves the elements in the range [first, last), to another range beginning at d_first. After this operation the elements in the moved-from range will still contain valid values of the appropriate type, but not necessarily the same values as before the move.

Contents

Parameters

first, last - the range of elements to move
d_first - the beginning of the destination range. If d_first is within [first, last), std::move_backward must be used instead of std::move.
Type requirements
-
InputIt must meet the requirements of InputIterator.
-
OutputIt must meet the requirements of OutputIterator.

Return value

Output iterator to the element past the last element moved (d_first + (last - first))

Complexity

Exactly last - first move assignments.

Possible implementation

template<class InputIt, class OutputIt>
OutputIt move(InputIt first, InputIt last, 
                    OutputIt d_first)
{
    while (first != last) {
        *d_first++ = std::move(*first++);
    }
    return d_first;
}

Notes

When moving overlapping ranges, std::move is appropriate when moving to the left (beginning of the destination range is outside the source range) while std::move_backward is appropriate when moving to the right (end of the destination range is outside the source range).

Example

The following code moves thread objects (which themselves are not copyable) from one container to another.

#include <iostream>
#include <vector>
#include <list>
#include <iterator>
#include <thread>
#include <chrono>

void f(int n)
{
    std::this_thread::sleep_for(std::chrono::seconds(n));
    std::cout << "thread " << n << " ended" << '\n';
}

int main()
{
    std::vector<std::thread> v;
    v.emplace_back(f, 1);
    v.emplace_back(f, 2);
    v.emplace_back(f, 3);
    std::list<std::thread> l;
    // copy() would not compile, because std::thread is noncopyable
    std::move(v.begin(), v.end(), std::back_inserter(l));
    for(auto& t : l) t.join();
}

Output:

thread 1 ended
thread 2 ended
thread 3 ended

See also

moves a range of elements to a new location in backwards order
(function template) [edit]
(C++11)
obtains an rvalue reference
(function template) [edit]