Swift 3 Unsafe Pointer

Question

I am migrating from Swift 2 to Swift 3 and I am stuck at one point.

Swift 2

let arr = UnsafePointer<UInt32>(UnsafePointer<UInt8>(buf).advanced(by: off)) let msk = arr[0].bigEndian & 0x7fffffff

I get an error on first line saying

'init' is unavailable: use 'withMemoryRebound(to:capacity:_)' to temporarily view memory as another layout-compatible type.

I tried to use withMemoryoRebound method but I am not sure about the parameters. As per this docuentation, UnsafePointer<> has been replaced by UnsafeRawPointer. So I changed my code as below

let arr = UnsafeRawPointer(UnsafePointer<UInt8>(buf).advanced(by: off)) let msk = arr[0].bigEndian & 0x7fffffff

But here on the second line it says

Type 'UnsafeRawPointer' has no subscript members

How can I successfully convert it to Swift 3?

This might be what you are looking for: How to get bytes out of an UnsafeMutableRawPointer? — Martin R
– Martin R, Commented Nov 16, 2016 at 17:35

kevin · Accepted Answer · 2017-02-03 22:41:54Z

This is how you can do that operation using withMemoryRebound: Capacity in this case is 1, as you are only looking at the first element of the resulting array.

let arr = UnsafePointer<UInt8>(buf).advanced(by: off) let msk = arr.withMemoryRebound(to: UInt32.self, capacity: 1) { p in return p[0].bigEndian & 0x7fffffff }

Tibor Bödecs · Accepted Answer · 2017-02-03 21:56:55Z

I think you are looking for something like this:

let ppp = UnsafePointer<UInt8>(buf).advanced(by: off) let arr = unsafeBitCast(ppp, to: UnsafeMutablePointer<UInt32>.self)

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