Hi,
On Dec 5, 2010, at 12:39 PM, Dennis Birch wrote:
> - (id)initWithFrame:(NSRect)frame {
> self = [super initWithFrame:frame];
> if (self) {
> // Initialization code here.
> TileColumn *allColumns[boardDimension - 1];
The above declaration is wrong for what you're trying to accomplish. You want
the array to have boardDimension elements, not boardDimension - 1 elements.
> for (int i = 0; i < boardDimension; i++)
> {
> TileColumn *column = [[TileColumn alloc] init];
> allColumns[i] = column;
On the last pass through this loop, when i == boardDimension - 1, you're
writing past the end of the array. Since you've declared the array to have
boardDimension - 1 elements, the largest valid index into it is boardDimension
- 2.
> }
>
> gameColumns = [NSArray arrayWithObjects:allColumns count:
> boardDimension];
Here, NSArray will read past the end of allColumns. allColumns has been
declared with boardDimension - 1 elements, but you're telling NSArray that it
has boardDimension elements.
> }
> return self;
> }
> I've run into a showstopper with my first project on my own (i.e. not a
> project from a book). I've created a custom View subclass, and when I try to
> instantiate an array of another custom subclass, it completely fails to do
> so, but doesn't produce any meaningful errors. I can see that it's failing in
> the debugger because after stepping after the line "TileColumn
> *allColumns[boardDimension - 1]", the array remains with a member count of -1.
If you step after the line "TileColumn *allColumns[boardDimension - 1]",
nothing has happened, yet. That's just a declaration.
Or am I misunderstanding, and you mean you have stepped repeatedly after that
line, through the loop?
Also, what you mean "array remains with a member count of -1"? Which array?
How are you assessing the member count? The allColumns array is a C array,
which doesn't know its element count. The gameColumns array, which I assume is
an instance variable of type NSArray*, is nil until you assign to it in the
last statement before the return. After that assignment, it will be a pointer
to an NSArray with boardDimension elements (or it will have failed with an
exception if something is very wrong, like some element of allColumns is still
nil).
> In the for loop, the line "allColumns[i] = column;" doesn't produce any
> errors but doesn't change the array.
Doesn't change which array? allColumns? That's basically impossible. How are
you determining this?
Is there any chance that you're trying to debug a release build (or any build
that has optimizations enabled)? An optimized build will be very confusing to
debug.
Finally, something to consider: there's nothing wrong with the technique you've
used of populating a C array and then building an NSArray from that C array.
However, you might consider creating an NSMutableArray that starts empty and
then, during the for loop, each TileColumn is added to it. If you create the
NSMutableArray with +arrayWithCapacity: or -initWithCapacity:, you'll even
avoid reallocation as you add elements to the array.
Cheers,
Ken
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