Ok, and I also am working with a coding table, several bins of static values
that will not change.. The bins have entries of 8, 16, 32, or 64 elements...
I just made those methods do:
-(float *)k1 {
static float k1[] = {
1.0f, 2.0f, ... (64 elements)
};
return k1;
}
Is this safe to do?
Sent from my iPhone
On Mar 3, 2015, at 12:46 PM, Jens Alfke <[email protected]> wrote:
>
>> On Mar 3, 2015, at 12:21 PM, Patrick Collins <[email protected]>
>> wrote:
>>
>> Right... But I guess what's not clear to me is, when does one use malloc
>> over the stack version? Is it only when you have a stack overflow? Or is
>> there some magic number of elements that fall under a
>> best-practice-use-malloc rule?
>
> If the array has to outlive the function that created it, then clearly you
> have to use malloc (or a passed-in buffer.)
>
> If it’s purely temporary to the function, then you have a choice. It’s not a
> clear-cut choice because it’s not easy to predict how much stack space you
> have. It varies by OS and even by version. On OS X the main thread gets a
> goodly amount (I’m vaguely remembering 32MB?) while background threads by
> default get much less. I don’t know whether iOS differs. Also, of course,
> some amount of stack will already have been used up by the time your function
> is called. And if your function could recurse, then of course things get much
> scarier.
>
> My rule of thumb is that I’ll allocate “a few kbytes” on the stack, otherwise
> I go to malloc. These days maybe 16k? But I tend to write libraries that can
> get used in lots of places in different people’s apps. If you own the app and
> know that function will run on the main thread without a deep call stack, you
> can safely put megabytes on the stack.
>
> Another useful thing to know is that nowadays C allows variable-size arrays
> in local variables. So this is legal (and convenient):
> unsigned n = …some computation…;
> float myArray[n];
>
> —Jens
>
> PS: OT, but one of the things I like about the Go language
> <http://golang.org> is that it uses growable stacks, so you never have to
> worry about running out of stack space. And as a side benefit, it creates
> threads with tiny stacks (2kbytes!) which makes threads insanely cheap.
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