How to pass a multidimensional array by reference when it has dynamic bounds?

Question

I have an int array myArray[x][y] and I wish to pass this to a function by reference, but it seems like it either needs constant bounds or some odd pointer workaround? How do I do this properly?

I already looked there and it did not seem to compile when I tried the variants included there, this is a much simpler case — user1947180, Feb 12 '13 at 15:13

score 0 · Accepted Answer · answered Feb 12 '13 at 15:12

0

An array with automatic storage duration always requires compile-time constant bounds. The fact that you can do int array[x]; where x is not a compile-time constant in GCC is merely a non-portable extension. Indeed, you cannot pass such a non-standard array by reference to a function.

You could just pass the bounds along with the array, but you're much better off using a standard container such as std::vector.

answered Feb 12 '13 at 15:12

Joseph Mansfield

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but since it is multidimensional wouldn't it be a vector of vectors? – user1947180 Feb 12 '13 at 15:14
@user1947180 Yes, it would be: `std::vector> array(x, std::vector(y));` – Joseph Mansfield Feb 12 '13 at 15:15
Does that initialize them to 0 by default? – user1947180 Feb 12 '13 at 15:16
Or, if you want/need to have the array as a single memory block, use a single vector and index it like `v[x + rowLength*y]`. – Alex Feb 12 '13 at 15:17
@user1947180 Yes, it will. – Joseph Mansfield Feb 12 '13 at 15:20

score 0 · Answer 2 · answered Feb 12 '13 at 15:24

0

Try:

template<int X, int Y>
void ArrayFn( int (&in)[X][Y] )
{
    in[X-1][Y-1] = 666; // or whatever
}

And call it like:

int arr[3][3];
ArrayFn( arr );

answered Feb 12 '13 at 15:24

Grimm The Opiner

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How to pass a multidimensional array by reference when it has dynamic bounds?

2 Answers2