[swift-users] C Pointers and Memory

[Dmitri Gribenko]

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

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