[swift-users] C Pointers and Memory

[James Campbell]

​Do you know of any resources to brush up on the pointer aspect of swift ? ​

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On 29 July 2016 at 09:10, Dmitri Gribenko <gribozavr at gmail.com> wrote:

> On Fri, Jul 29, 2016 at 12:55 AM, James Campbell <james at supmenow.com>
> wrote:
> > So this:
> >
> > if let data = someArrayGeneratingFunction() {
> >   cFunction(UnsafeMutablePointer(data))
> > }
> >
> > Has issues with the array passed to c getting corrupted, but this
> doesn't:
> >
> > let data = someArrayGeneratingFunction()
> >
> > if let data = data {
> >   cFunction(UnsafeMutablePointer(data))
> > }
>
> Neither piece of code is guaranteed to work.  (You are just getting
> lucky that the second one happens to work.)  Array-to-pointer
> conversion only extends the lifetime of the array until the immediate
> function call returns.  So after UnsafeMutablePointer(data) returns,
> the array can be freed.
>
> Use someArrayGeneratingFunction.withUnsafeMutableBuffer { ... } instead.
>
> Dmitri
>
> --
> main(i,j){for(i=2;;i++){for(j=2;j<i;j++){if(!(i%j)){j=0;break;}}if
> (j){printf("%d\n",i);}}} /*Dmitri Gribenko <gribozavr at gmail.com>*/
>
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