C++ return array from function [duplicate]

Solution 1:

You can't return n builtin array in c++.

If you are new to c++ and get confused about pointers you really don't want to use arrays (at least not builtin arrays). Use std::vector<int> instead, or if you only ever have a certain number of elements and want to express that (and really need the better performance) use boost::array<int, N>.(or even std::array<int, N>, if you program in C++11 (if you don't know whether or not you program in C++11 chances are that you don't). For example:

std::vector<int> myfunction(const std::vector<int>& my_array) {
  std::vector<int> f_array;
  for(int i = 0; i < my_array.size(); ++i)
    f_array.push_back(my_array[i]);
  return f_array;
}

boost::array<int, 2> myfunction(const boost::array<int, 2>& my_array) {
  boost::array<int, 2> f_array;
  f_array[0] = my_array[0];
  f_array[1] = my_array[1];
  return f_array;
}

You can then make your copying code simpler (look up the constructors and memberfunctions of whatever class you decide to use, as well as STL algorithms). Example:

std::vector<int> myfunction(const std::vector<int>& my_array) {
  std::vector<int> f_array(m_array);
  ...
  return f_array;
}

As another point your code has a bug in it: you define my_array as int my_array[1], meaning its an array with one element, but you access two elements (my_array[0] and my_array[1]), the access to my_array[1] is out of bounds (int foo[N] has place for N items, starting at index 0 and going to index N-1). I assume you really mean int my_array[2].

Solution 2:

std::array<int,2> myfunction(int * my_array)
{
    std::array<int,2> f_array;
    f_array[0] = my_array[0];
    f_array[1] = my_array[1];

    // modify f_array some more

    return f_array;
}

Note that as a parameter, int my_array[1] is exactly identical to int my_array[1000], int my_array[] or int * my_array. It's just a pointer, and the size value is meaningless. This doesn't apply to regular array declarations, just parameters.

To ensure that you're only being passed arrays of size 2, you can take the array by reference:

std::array<int,2> myfunction(int (&my_array)[2])

Solution 3:

If you ever only need two values I would have a look at std::pair, after all, that's what it's there for. It also have the proper copy (move in c++11) semantics to make this work correctly.