Difference between copy_backward and reverse_copy?

Question

I am reading C++ primer and saw these two functions that seem to have the same functionality. Could anyone help and tell me what is the difference between the two? Thanks.

You should bookmark this site: http://en.cppreference.com/w/ for future use. — Anon Mail, Dec 02 '15 at 17:49

score 10 · Accepted Answer · edited Dec 02 '15 at 17:50

10

reverse_copy actually puts the elements in reverse order.

1 2 3 4 5 - > 5 4 3 2 1

copy_backward simply copies the elements backwards, but preserves their relative order.

1 2 3 4 5

5 is copied first, but put in the last spot. So your output is still:

1 2 3 4 5

http://en.cppreference.com/w/cpp/algorithm/copy_backward

Copies the elements from the range, defined by [first, last), 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.

http://en.cppreference.com/w/cpp/algorithm/reverse_copy

Copies the elements from the range [first, last) to another range beginning at d_first in such a way that the elements in the new range are in reverse order.

edited Dec 02 '15 at 17:50

Martin York

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answered Dec 02 '15 at 17:47

Rivasa

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but whats the point of `std::copy_backward` if we can just `std::copy` ? – 0xB00B Feb 18 '23 at 11:16
@0xB00B copy and copy_backwards handle overlapping ranges differently – Cubbi May 09 '23 at 16:28

score 2 · Answer 2 · edited Dec 02 '15 at 17:50

std::copy_backwards does:

Copies the elements from the range, defined by [first, last), 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.

std::reverse_copy

Copies the elements from the range [first, last) to another range beginning at d_first in such a way that the elements in the new range are in reverse order.

So the difference is that std::copy_backwards start copying at the end and works backwards, keeping original positioning, whereas std::reverse_copy starts copying at the beginning going forward, but puts them in the reverse order.

Difference between copy_backward and reverse_copy?

2 Answers2