Thread: pointer/array question

hi i'm trying to understand the relation between pointers and arrays but i have a problem that i can't figure out myself.

i read that the name of an array in c is the adress of the first element of the array , but if that's true , i don't understand why this simple code doesn't work.

Code:

#include <stdio.h>

int main()
{
	int array[4][3] = { {1,2,3} , {4,5,6} , {7,8,9} , {10,11,12} };

	printf("%i\n",array);
	printf("%i\n",&array[0][0]);

	printf("%i\n",*array);
	printf("%i\n",*(&array[0][0]));

	return 0;
}

the problem is that when i try to dereference "array" the computer prints the adress of the first element instead of "1" whereas dereferencing "&array[0][0]" works perfect.
can somebody please explain to me what mistake i am making?

My knowledge of C isn't great but I am guessing the problem is that because you have declared a 2d array, deferencing it gives you the beginning of the first inner array so to speak. Adding an extra * produces the first value within that array.

Multidimensional arrays are implemented as arrays of pointers. What you have there is an array of size 4 of type int*. Each of int* points to an array of size 3 type int. *array then is the content of the first element of the pointer array, which is the address to the first element of the array it points to - this would be &array[0][0].

*(&array[0][0]) is a similar beast to *array. array[0][0] is equal to: *(*(array+0)+0), that is the content of the first element in the int* array dereferenced, which gives you the content of the first element in the array pointed to by that pointer. So expanding it out, you have

Code:

*(&(*(*(array+0)+0)))

the &* cancels out, so you are left with:

Code:

*(*(array+0)+0)

which is '1'.

I know that is clear as mud... but there it is.

Hope it helps,
Steve

Originally Posted by freespace

Multidimensional arrays are implemented as arrays of pointers. What you have there is an array of size 4 of type int*.

Nope. Let's not start confusing things like that.
http://67.40.109.61/torek/c/pa.html

Here array in value context has type int (*)[3].