How to pass a N-dimensional array to a function?

[LarryChen]

If a function takes N-dimensional array as a parameter, what is generic way to do that? I couldn't figure out a nice way to do that. Any comments are welcome! Thanks.

[2kaud]

Have a look at
http://stackoverflow.com/questions/6...tion-parameter
http://stackoverflow.com/questions/1...ensional-array
http://stackoverflow.com/questions/4...se-arrays-in-c

[razzle]

Any comments are welcome

If you want generiticity there's a Boost library class called MultiArray.

[LarryChen]

If you want generiticity there's a Boost library class called MultiArray.

We don't use Boost library. I want to implement one on my own. Thanks.

[LarryChen]

Have a look at
http://stackoverflow.com/questions/6...tion-parameter
http://stackoverflow.com/questions/1...ensional-array
http://stackoverflow.com/questions/4...se-arrays-in-c

The links you gave are all about two-dimensional array. I am talking about N-dimensional array. Here N could be any number. Any idea? Thanks.

[razzle]

I am talking about N-dimensional array. Here N could be any number. Any idea?

Yes, only 1-dimensional programmers use N-dimensional arrays.

In C++ there's almost always a better data structure than an N-dimensional array (where N is higher than 2).

I suggest you start learning about the alternatives. Use Boost.MultiArray for cases where there really is no alternative and you'll soon realize you never need to. It's an emergency exit you never have to use.

[2kaud]

If a function takes N-dimensional array as a parameter, what is generic way to do that? I couldn't figure out a nice way to do that. Any comments are welcome! Thanks.

If the dimensions and size are known at compile time then it's trivial. If the dimensions/size are run-time related then one way that I've used in the past (which may not be the best way ) is to have the N-dimensional array as contiguous memory and pass memory pointer, the number of dimensions and the size of each dimension as variable number of parameters to the function. Or you could have a vector with the size of each dimension and pass the memory pointer and the vector. Or have a struct that contains the memory pointer and a vector for the dimension sizes (you can get the number of dimensions from the number of elements in the vector) and pass the struct as reference to the function. If using a struct then the operator() could be overloaded to allow array access with a variable number of parameters and the constructor used to allocate the memory and create the vector of dimension sizes. A skeleton struct could be something like

template <typename T>
struct myarray {
	void *arrptr;

	vector <int> dimens;

	myarray(int nodim, ...)
	{
		//...
	}

	T& operator()(int first, ...)
	{
		//...
	}

	~myarray()
	{
		//...
	}
};

[GeoRanger]

Are you just looking for the basic but non-obvious syntax?

// The crucial thing to remember here is to read non-trivial pointer declarations backward
// but with grouping by parentheses.  So, "pArray is a constant pointer to an aray of
// 10 x 8 x 3 constant integers".
void MyFunction(int const (* const pArray)[10][8][3], int nRows)
{
    for (int i = 0; i < nRows; ++i)
    {
        int x = pArray[i][9][7][2];
    }
}

void MyOtherFunction(void)
{
    // Of course in a real program you wouldn't use the hard-coded constants and
    // most people would probably want a typedef.
    int (* pArrayOnHeap)[10][8][3] = nullptr;
    // All but the first dimension must match the declaration.
    pArrayOnHeap = new (int[2][10][8][3]); // Should use a smart pointer.
    MyFunction(pArrayOnHeap, 2);

    int arrayOnStack[4][10][8][3];
    // _countof() will only count the first dimension
    MyFunction(arrayOnStack, _countof(arrayOnStack));

    delete [] pArrayOnHeap;
}

Hope this helps,
GeoRanger