< cpp‎ | algorithm
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
Search operations
(C++11)                (C++11)(C++11)

Modifying sequence operations
Copy operations
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
Sampling operations

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Lexicographical comparison operations
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
Defined in header <algorithm>
template< class BidirIt1, class BidirIt2 >
BidirIt2 copy_backward( BidirIt1 first, BidirIt1 last, BidirIt2 d_last );
(constexpr since C++20)

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

The behavior is undefined if d_last is within (firstlast]. std::copy must be used instead of std::copy_backward in that case.


[edit] Parameters

first, last - the range of the elements to copy from
d_last - the end of the destination range
Type requirements
BidirIt must meet the requirements of LegacyBidirectionalIterator.

[edit] Return value

Iterator to the last element copied.

[edit] Complexity

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

[edit] Notes

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

[edit] Possible implementation

template<class BidirIt1, class BidirIt2>
BidirIt2 copy_backward(BidirIt1 first, BidirIt1 last, BidirIt2 d_last)
    while (first != last)
        *(--d_last) = *(--last);
    return d_last;

[edit] Example

#include <algorithm>
#include <iostream>
#include <numeric>
#include <vector>
int main()
    std::vector<int> source(4);
    std::iota(source.begin(), source.end(), 1); // fills with 1, 2, 3, 4
    std::vector<int> destination(6);
    std::copy_backward(source.begin(), source.end(), destination.end());
    std::cout << "destination contains: ";
    for (auto i: destination)
        std::cout << i << ' ';
    std::cout << '\n';


destination contains: 0 0 1 2 3 4

[edit] Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 1206 C++98 1. the behavior was well-defined if d_last == last
2. the behavior was undefined if d_last == first
1. made undefined
2. made well-defined

[edit] See also

copies a range of elements to a new location
(function template) [edit]
copies a range of elements in backwards order