std::ranges::move_backward, std::ranges::move_backward_result

Since C++20

Header: <algorithm>

  1. Moves the elements in the range, defined by [first,last), to another range [result - N,result), where N = ranges::distance(first, last). The elements are moved in reverse order (the last element is moved first), but their relative order is preserved. The behavior is undefined if result is within (first, last]. In such a case, ranges::move may be used instead.

# Declarations

Call signature

template< std::bidirectional_iterator I1, std::sentinel_for<I1> S1,
std::bidirectional_iterator I2 >
requires std::indirectly_movable<I1, I2>
constexpr move_backward_result<I1, I2>
move_backward( I1 first, S1 last, I2 result );

(since C++20)

template< ranges::bidirectional_range R, std::bidirectional_iterator I >
requires std::indirectly_movable<ranges::iterator_t<R>, I>
constexpr move_backward_result<ranges::borrowed_iterator_t<R>, I>
move_backward( R&& r, I result );

(since C++20)

Helper types

template< class I, class O >
using move_backward_result = ranges::in_out_result<I, O>;

(since C++20)

# Parameters

# Return value

{last, result - N}.

# Notes

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

# Example

#include <algorithm>
#include <iostream>
#include <string>
#include <string_view>
#include <vector>
 
using Vec = std::vector<std::string>;
 
void print(std::string_view rem, Vec const& vec)
{
    std::cout << rem << "[" << vec.size() << "]: ";
    for (const std::string& s : vec)
        std::cout << (s.size() ? s : std::string{"·"}) << ' ';
    std::cout << '\n';
}
 
int main()
{
    Vec a{"▁", "▂", "▃", "▄", "▅", "▆", "▇", "█"};
    Vec b(a.size());
 
    print("Before move:\n" "a", a);
    print("b", b);
 
    std::ranges::move_backward(a, b.end());
 
    print("\n" "Move a >> b:\n" "a", a);
    print("b", b);
 
    std::ranges::move_backward(b.begin(), b.end(), a.end());
    print("\n" "Move b >> a:\n" "a", a);
    print("b", b);
 
    std::ranges::move_backward(a.begin(), a.begin()+3, a.end());
    print("\n" "Overlapping move a[0, 3) >> a[5, 8):\n" "a", a);
}

# See also