Question

Please consider the following 2-D Array:

int array[2][2] = {
                    {1,2},
                    {3,4}
                  };

As per my understanding:
– ‘array’ represents the base address of the 2-D array (which is the same as address of the first element of the array, i.e array[0][0]).

• The actual arrangement of a 2-D Array in memory is like a large 1-D Array only.

• Now, I know that base address = array. Hence, I should be able to reach the Memory Block containing the element: array[0][0].

• If I forget about the 2-D array thing & try to treat this array as a simple 1-D array:
  array[0] = *(array+0) gives the base address of the first array & NOT the element array[0][0]. Why?

• A 2-D array does not store any memory address (like an Array of Pointers).

• If I know the base address, I must be able to access this memory as a linear 1- Dimensional Array.

Please help me clarify this doubt.

Thanks.

Answer 1

Arrays are not pointers.

In most circumstances¹, an expression of type “N-element array of T” will be converted (“decay”) to an expression of type “pointer to T“, and the value of the expression will be the address of the first element of the array.

The type of the expression array is “2-element array of 2-element array of int“. Per the rule above, this will decay to “pointer to 2-element array of int (int (*)[2]) in most circumstances. This means that the type of the expression *array (and by extension, *(array + 0) and array[0]) is “2-element array of int“, which in turn will decay to type int *.

Thus, *(array + i) gives you the i‘th 2-element array of int following array (i.e., the first 2-element array of int is at array[0] (*(array + 0)), and the second 2-element array of int is at array[1] (*(array + 1)).

If you want to treat array as a 1-dimensional array of int, you’ll have to do some casting gymnastics along the lines of

int *p = (int *) array;
int x = p[0];

or

int x = *((int *) array + 0);

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^{1. The exceptions are when the array expression is an operand of the sizeof or unary & operators, or is a string literal being used to initialize another array in a declaration.}