[swift-users] How to malloc in Swift 3

[Jens Persson]

What is the difference between:
ptr.storeBytes(of: x, toByteOffset: offset, as: type(of: x))
ptr.advanced(by: offset).assumingMemoryBound(to: type(of: x)).pointee = x
?
I noticed that the former traps if storing to a misaligned offset while the
latter is happy to do that, and I saw it mentioned as a requirement in the
documentation, but other than that I'm not sure what would be the pros and
cons of using the former / latter?
/Jens


On Fri, Sep 23, 2016 at 10:23 PM, Joe Groff via swift-users <
swift-users at swift.org> wrote:

>
> > On Sep 23, 2016, at 1:55 AM, Gerriet M. Denkmann via swift-users <
> swift-users at swift.org> wrote:
> >
> >
> >> On 23 Sep 2016, at 15:47, Gerriet M. Denkmann via swift-users <
> swift-users at swift.org> wrote:
> >>
> >> This used to work in Swift 2.2:
> >>
> >> var bitfield: UnsafeMutablePointer<UInt8>?
> >> bitfield = UnsafeMutablePointer<UInt8>( malloc( 888 ) )
> >>
> >> How is this written in Swift 3.0?
> >
> > To answer my own question:
> > This works:
> > var bitfield: UnsafeMutableRawPointer
> > bitfield = UnsafeMutableRawPointer( malloc(888))
> >
> > But then this stops working:
> > let theByte = self.bitfield[ 5 ]
> >
> > Somehow the bitfield must know that it is a field of bytes (not shorts,
> ints or whatever). But how?
>
> The RawPointer types provide methods that can load a value with a given
> offset and type for you. IIRC, `bitfield.load(fromByteOffset: 0, as:
> UInt8.self)` will do what you want.
>
> -Joe
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