[cairo] [cairo-commit] 3 commits - src/cairo-array.c src/cairoint.h src/cairo-types-private.h

[Bill Spitzak]

On 11/28/2010 12:08 AM, Andrea Canciani wrote:
> On Sun, Nov 28, 2010 at 4:36 AM, Bill Spitzak<spitzak at gmail.com>  wrote:
>> This code in the comment makes no sense to me:
>>
>>>>>> +    /* We allow an index of 0 for the no-elements case.
>>>>>> +     * This makes for cleaner calling code which will often look like:
>>>>>> +     *
>>>>>> +     *    elements = _cairo_array_index_const (array, num_elements);
>>>>>> +     *         for (i=0; i<  num_elements; i++) {
>>>>>> +     *        ... read elements[i] here ...
>>>>>> +     *    }
>>>>>> +     *
>>>>>> +     * which in the num_elements==0 case gets the NULL pointer here,
>>>>>> +     * but never dereferences it.
>>>>>> +     */
>>
>
> +     *    elements = _cairo_array_index_const (array, num_elements);
> should be
> +     *    elements = _cairo_array_index_const (array, 0);
>
> (same for the comment in _cairo_array_index)
>
> Andrea

That helps, but it still seems to require that zero not be treated 
specially.

I'm guessing that the user wants a pointer to the first of the range N 
.. N+num_elements (and knows for other reasons that this is not outside 
the array bounds).

However if num_elements is zero, this must not throw for the size of the 
array, as there is in fact a valid zero-length array at that point. 
Therefore it seems this function must never throw for n==size if this is 
to work.

If in fact this is never done except with zero, I would make a 
*different* call, perhaps called "cairo_array_get_array", that never 
throws and just returns the pointer to the array.