Thread: Returning two-dimensional array in C++

A vector of vectors may have too much overhead to be a replacement for small multidimensional stack array. (I believe there are cases where it is justified not to want dynamic allocations.)

By the way, do you want to return a copy of the array?

In that case, it might be meaningful to use an out parameter (the contents are copied to a suitable array provided by the caller).

If you don't want a copy, then you might try returning a pointer to pointer (int**).

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Best advice depends on what exactly you are doing this for...

Originally Posted by anon

A vector of vectors may have too much overhead to be a replacement for small multidimensional stack array. (I believe there are cases where it is justified not to want dynamic allocations.)

By the way, do you want to return a copy of the array?

In that case, it might be meaningful to use an out parameter (the contents are copied to a suitable array provided by the caller).

If you don't want a copy, then you might try returning a pointer to pointer (int**).

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Best advice depends on what exactly you are doing this for...

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.

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

--
Mats

You should be able to return a pointer to an array in a class. Let me work on it for few minutes.

Not very pretty:

Code:

#include <iostream>

typedef int myarray[5][5];

class myclass
{
    myarray arr;

public:
    myclass() {
	for(int i = 0; i < 5; i++)
	{
	    for(int j = 0; j < 5; j++)
		arr[j][i] = i * j;
	}
    }
    friend std::ostream &operator<<(std::ostream &os, const myclass &c);
    myarray * getArray()
	{
	    return &arr;
	}


};

std::ostream &operator<<(std::ostream &os, const myclass &c) 
{
    for(int i = 0; i < 5; i++)
    {
	for(int j = 0; j < 5; j++)
	    os << c.arr[j][i] << " ";
	
	os << std::endl;
    }
    
    return os;
}



int main()
{
    myclass c;
    int (*p)[5][5];
   
    std::cout << c;
  
    p = c.getArray();
    for(int i = 0; i < 5; i++)
    {
	for(int j = 0; j < 5; j++)
	    std::cout << (*p)[j][i] << " ";
	std::cout << std::endl;
    }
    return 0;

}

--
Mats