Move first element of Vector to last element

Question

I want to move first element of vector to the end of vector.

v = {1,2,3,4} after this should be like this

v= {2,3,4,1}

my compiler version is gcc version 4.4.3 (Ubuntu 4.4.3-4ubuntu5.1)

I know in Vc11 we can use std::move to move element. but how can I do this in above version of compiler?

Also, `std::move` does not move things in that sense. Anyway, there are good examples here: [`std::rotate`](http://en.cppreference.com/w/cpp/algorithm/rotate). — juanchopanza, Oct 13 '14 at 18:02
Funnily enough, you can also call `remove(v.begin(), v.end(), v.at(0))` if there are no duplicates. I wouldn't do that, but... funnily enough. :) — Yam Marcovic, Oct 13 '14 at 18:11
@YamMarcovic That wouldn't work. At least it wouldn't be guaranteed to. — juanchopanza, Oct 13 '14 at 18:12
@juanchopanza You're right - it's not guaranteed that the elements will retain their original state. — Yam Marcovic, Oct 13 '14 at 18:14
@MuhammadZaighum: Because `deque` has efficient `pop_front()`/`push_front()` besides the `*_back()` variants, only available in `vector`. — rodrigo, Oct 13 '14 at 18:44

Columbo · Answer 1 · 2014-10-13T18:16:53.660

3

As noted in the comments, std::rotate is one possible way:

std::rotate( v.begin(), v.begin() + 1, v.end() );

edited Oct 13 '14 at 18:16

answered Oct 13 '14 at 18:10

Columbo

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`std::vector` doesn't have a `pop_front()`, for a good reason. It would be quite inefficient. – juanchopanza Oct 13 '14 at 18:14
Your new version would "work", but is unnecessarily inefficient. – juanchopanza Oct 13 '14 at 18:16
@juanchopanza Why, is it O(N)? – Columbo Oct 13 '14 at 18:17

score 3 · Accepted Answer · answered Jan 13 '15 at 07:44

3

There's a std::rotate algorithm in the standard library:

std::rotate(ObjectToRotate.begin(),
            ObjectToRotate.end()-1, // this will be the new first element
            ObjectToRotate.end());

answered Jan 13 '15 at 07:44

For me this swaps the first and last elements instead of just moving the first item to the back. – Alex Oct 05 '21 at 20:50

score 1 · Answer 3 · answered Oct 13 '14 at 18:10

You should consider using std::rotate or if you want it the ugly way: Create a function that safes the last and the first element in local variables, create a new local vector, but the last element as first in the vector. Put begin+1 till end-1 in the vector and then the first element.

Move first element of Vector to last element

3 Answers3

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