Return an array in c++

Question

Suppose I have an array

int arr[] = {...};
arr = function(arr);

I have the function as

 int& function(int arr[])
 {
//         


        

Answer 1

You're returning a reference to an int, not a reference to an array.

You want :

(int*)& function(int arr[])
{
     /// rest of the code
     return arr;
}

That said, as others already said, that's not good practice.

Answer 2

I think your best bet is to return it as a pointer to an array. Here is an example:

{
   ...
   int newLength = 0;
   int* arr2 = ChangeArray(arr, length, newLength);
   ...
   delete[] arr2;
}

int* ChangeArray(int arr[], int length, int& newLength)
{
   // reversing the number - just an example
   int* newArr = new int[length];
   for(int i = 0; i < length; i++)
   {
      newArr[i] = arr[length-i-1];
      newLength++;
   }
   return newArr;
}

Answer 3

Use std:: vector like this.

std::vector<int> function(const std::vector<int>& arr)
{
  return arr;
}

An array like

int arr[] = {...};

is not useful to be returned from a function because its not able to copy itself.

Answer 4

if not necessary, don't use it. you can just pass a reference of an array, such as:

void foo(std::vector<int> &v) {
    for (int i = 0; i < 10; ++ i) {
        v.push_back(i);
    }
}

if you use:

std::vector<int> foo() {
    std::vector<int> v;
    for (int i = 0; i < 10; ++ i)
        v.push_back(i);

    return v;
}

there'll be a copy process of the container, the cost is expensive.

FYI: NRVO maybe eliminate the cost

Answer 5

The semantics of array passing and return can be quite confusing. Use a std::vector instead.