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std::move_backward

From cppreference.com
< cpp‎ | algorithm
 
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
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(C++17)
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(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
(C++11)
(C++11)
move_backward
(C++11)
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Generation operations
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(until C++17)(C++11)
(C++20)(C++20)
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(C++17)

Sorting and related operations
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C library
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template< class BidirIt1, class BidirIt2 >
BidirIt2 move_backward( BidirIt1 first, BidirIt1 last, BidirIt2 d_last );
(since C++11)
(constexpr since C++20)

Moves the elements from the range [firstlast), to another range ending at d_last. The elements are moved in reverse order (the last element is moved first), but their relative order is preserved.

If d_last is within (firstlast], the behavior is undefined. In this case, std::move may be used instead.

Contents

[edit] Parameters

first, last - the range of the elements to move
d_last - end of the destination range
Type requirements
-
BidirIt1, BidirIt2 must meet the requirements of LegacyBidirectionalIterator.

[edit] Return value

Iterator in the destination range, pointing at the last element moved.

[edit] Complexity

Exactly std::distance(first, last) move assignments.

[edit] Possible implementation

template<class BidirIt1, class BidirIt2>
BidirIt2 move_backward(BidirIt1 first, BidirIt1 last, BidirIt2 d_last)
{
    while (first != last)
        *(--d_last) = std::move(*(--last));
 
    return d_last;
}

[edit] 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).

[edit] Example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <string>
#include <string_view>
#include <vector>
 
using container = std::vector<std::string>;
 
void print(std::string_view comment, const container& src, const container& dst = {})
{
    auto prn = [](std::string_view name, const container& cont)
    {
        std::cout << name;
        for (const auto &s : cont)
            std::cout << (s.empty() ? "∙" : s.data()) << ' ';
        std::cout << '\n';
    };
    std::cout << comment << '\n';
    prn("src: ", src);
    if (dst.empty())
        return;
    prn("dst: ", dst);
}
 
int main()
{
    container src{"foo", "bar", "baz"};
    container dst{"qux", "quux", "quuz", "corge"};
    print("Non-overlapping case; before move_backward:", src, dst);
    std::move_backward(src.begin(), src.end(), dst.end());
    print("After:", src, dst);
 
    src = {"snap", "crackle", "pop", "lock", "drop"};
    print("Overlapping case; before move_backward:", src);
    std::move_backward(src.begin(), std::next(src.begin(), 3), src.end());
    print("After:", src);
}

Output:

Non-overlapping case; before move_backward:
src: foo bar baz
dst: qux quux quuz corge
After:
src: ∙ ∙ ∙
dst: qux foo bar baz
Overlapping case; before move_backward:
src: snap crackle pop lock drop
After:
src: ∙ ∙ snap crackle pop

[edit] See also

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