std::move_backward

Defined in header `<algorithm>`
template< class BidirIt1, class BidirIt2 > BidirIt2 move_backward( BidirIt1 first, BidirIt1 last, BidirIt2 d_last );		(since C++11) (until C++20)
template< class BidirIt1, class BidirIt2 > constexpr BidirIt2 move_backward( BidirIt1 first, BidirIt1 last, BidirIt2 d_last );		(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.

The behavior is undefined if d_last is within (first, last]. std::move must be used instead of std::move_backward in that case.

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 BidirectionalIterator.

Return value

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

Complexity

Exactly last - first move assignments.

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;
}

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

Run this code

#include <algorithm>
#include <vector>
#include <string>
#include <iostream>

int main()
{
    std::vector<std::string> src{"foo", "bar", "baz"};
    std::vector<std::string> dest(src.size());

    std::cout << "src: ";
    for (const auto &s : src)
    {
        std::cout << s << ' ';
    }   
    std::cout << "\ndest: ";
    for (const auto &s : dest)
    {
        std::cout << s << ' ';
    }   
    std::cout << '\n';

    std::move_backward(src.begin(), src.end(), dest.end());

    std::cout << "src: ";                                                       
    for (const auto &s : src)
    {
        std::cout << s << ' ';
    }   
    std::cout << "\ndest: ";
    for (const auto &s : dest)
    {
        std::cout << s << ' ';
    }   
    std::cout << '\n';
}

Output:

src: foo bar baz 
dest:    
src:    
dest: foo bar baz

Language
Headers
Freestanding and hosted implementations
Named requirements
Language support library
Concepts library (C++20)
Diagnostics library
Utilities library
Strings library
Containers library
Algorithms library
Iterators library
Numerics library
Input/output library
Localizations library
Regular expressions library (C++11)
Atomic operations library (C++11)
Thread support library (C++11)
Filesystem library (C++17)
Technical Specifications