std::move_backward
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Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
(C++17)
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(C++17)
(C++11)
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(C++20)(C++20)
(C++17)
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Defined in header
<algorithm>
template< class BidirIt1, class BidirIt2 >
BidirIt2 move_backward( BidirIt1 first, BidirIt1 last, BidirIt2 d_last );
(since C++11) BidirIt2 move_backward( BidirIt1 first, BidirIt1 last, BidirIt2 d_last );
(constexpr since C++20)
Moves the elements from the range [first, last), 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 (first, last], the behavior is undefined. In this case, std::move may be used instead.
Contents
[edit] Parameters
first, last
-
the pair of iterators defining the source range of 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
Run this code
#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++20)
(algorithm function object)[edit]