Get 5 last array objects C++

Question

A simple task, but I don't remember the syntax for C++.

int array[n];

I need to get the last 5 objects of the array.

array.slice(array.length - 5, 1)??

Answer 1

In short

Algorithms will be your friends:

int last[5]; 
std::copy(array+n-5, array+n, last); 

More details

First, the variable length array is not standard C++. So the following code is only portable and valid if n is a constant expression:

int array[n]; 

So the better approach would be to use vectors of int. The advantage is that their size may evolve dynamically when needed:

vector<int> varray(n); 

If really you want to use variable raw arrays, you could use memory allocation, but this is cumbersome since you have to take a lot of precautions (e.g. deleting the allocated object in the end):

int *array = new int[n];

The solution with raw arrays is displayed above. I leave it up to you to generalize it to the k last elements.

The vector variant is very similar:

vector<int> vlast(5);
copy(varray.end()-vlast.size(), varray.end(), vlast.begin()); 

Note that the copy is more dynamic, since the number of elements will depend on the size of the output vector.

Attention - risk of UB: I leave you as an exercise to adapt the code for both solutions to the case where the size of the array would be smaller than 5.

Now if you like algorithms, it's worth also to look at iterators, because they allow you to do cool tricks like:

copy(vlast.begin(), vlast.end(), ostream_iterator<int>(cout," ")); // display
cout<<endl; 

Online demo

Still not convinced by vectors ? Then have a look at these two other vector variants:

vector<int> vlast2(varray.end()-5, varray.end());  // powerful constructor
vector<int> vlast3(varray.rbegin(), varray.rbegin()+5); // and in reverse order