Thread: Returning two-dimensional array in C++

gcc (and g++) doesn't seem to allow functions returning arrays.

I believe that it is not possible to return an array in both C and C++.

Returning a pointer to pointer won't work, since you loose the dimension of the array. You will need to indicate at least the last dimension of the array.

Yes, so we can return a pointer to the first element of the array. Since I am not sure of the syntax, I shall take the liberty of using a typedef:

Code:

class MyClass {
  public:
  typedef int(*ArrayType)[5];
  ArrayType getArray()
  {
    return array;
  }

  private:
  int array[5][5];
};

So there is no way to do it without vectors?

See above. The thing is, vectors can make things easier.

(Hm, maybe I should've posted in the C-forum instead, given the devlopement of this thread. Oh well..)

This is part of C++'s C heritage, so you will face the same problem.

Originally Posted by laserlight

I believe that it is not possible to return an array in both C and C++.

Yes, I think it relates back to the "you can't assign arrays" that C also has in it's basic setup.

--
Mats

If you are sure you want to be able to modify the array from outside the class, I don't see much point in making it private in the first place.

Originally Posted by Drogin

I don't really need to modify it. I just want to check the data. So it can be defined as const pointer.

Are you sure that you don't want to "check the data" in a member/friend function?

--
Mats

You still haven't addressed why you are so anti-vector, however.

Originally Posted by Elysia

You still haven't addressed why you are so anti-vector, however.

Have you considered that not everyone should have to motivate their design decisions with you?

--
Mats

Have you considered that I want to know why the OP is so anti-vector?
I'm not the only one suggesting the idea to use a vector. Laserlight proposed (or clarified) that they made things easier, so I'd like to know (especially with Java background!) why someone is so anti-vector.

But it's also part of suggesting a solution. Or helping solve the problem or gaining a better understanding of the problem.
Is the OP afraid of C++ objects? Is the OP afraid of vector? Is it speed concerns? Is it memory concerns?
And this is only the 2nd. If it gets ignored after the 2nd time, then maybe it's time to start evaluating if it's ignored on purpose.
Even so, it's also somewhat rude to ignore posts, especially from people trying to help. It's all for the sake of getting a better understanding of the problem.

There's nothing wrong with using arrays, if you don't want vectors. It's definitely possible to return an array, but it looks ugly:

Code:

class MyClass
{
    private:
        /* I assume you want the const-ness of this
             array to be implementation defined: */
        int array[5][5];
        /* Otherwise, you can of course explicitly
            make it mutable or const, and get rid of
            the unecessary getter function, below: */

    public:
        /* Const getter-function: */
        const int (&getArray() const)[5][5] { return array; }

        /* Non-const getter: */
        int (&getArray())[5][5] { return array; }
};

This is more direct and simple than returning a pointer to a pointer to an integer. You could also make the array dimensions into a macro so you never need to repeat the '[5][5]'.

int ** getArray()

this doesn't help you keep track of the array dimensions though if they're ever something other than 5 and 5; you'll need something like:

unsigned int get1DLength()

and

unsigned int get2DLength(int 1dPos)

this is probably not the best way to do it tho.