Cannot Initialise Variable for type Unsafepointer Swift 3.0 conversion

Question

Hi I am converting existing swift 2.0 code to swift 3.0 but came across an error while conversion:

Cannot invoke initializer for type 'UnsafePointer' with an argument list of type '(UnsafeRawPointer)'

Here is my code:

extension Data { var hexString : String { let buf = UnsafePointer<UInt8>(bytes) // here is the error let charA = UInt8(UnicodeScalar("a").value) let char0 = UInt8(UnicodeScalar("0").value) func itoh(_ i: UInt8) -> UInt8 { return (i > 9) ? (charA + i - 10) : (char0 + i) } let p = UnsafeMutablePointer<UInt8>.allocate(capacity: count * 2) for i in 0..<count { p[i*2] = itoh((buf[i] >> 4) & 0xF) p[i*2+1] = itoh(buf[i] & 0xF) } return NSString(bytesNoCopy: p, length: count*2, encoding: String.Encoding.utf8.rawValue, freeWhenDone: true)! as String } }

Why not simply var hexString : String { return self.map { String(format:"%02x", $0) }.joined() } ? — vadian
– vadian, Commented Sep 12, 2017 at 6:43
If an answer helped then you can accept it by clicking on the check mark. — Martin R
– Martin R, Commented Sep 18, 2017 at 8:32

Martin R · Accepted Answer · 2017-09-12 07:12:19Z

In Swift 3 you have to use withUnsafeBytes() to access the raw bytes of a Data value. In your case:

withUnsafeBytes { (buf: UnsafePointer<UInt8>) in for i in 0..<count { p[i*2] = itoh((buf[i] >> 4) & 0xF) p[i*2+1] = itoh(buf[i] & 0xF) } }

Alternatively, use the fact that Data is a collection of bytes:

for (i, byte) in self.enumerated() { p[i*2] = itoh((byte >> 4) & 0xF) p[i*2+1] = itoh(byte & 0xF) }

Note that there is another problem in your code:

NSString(..., freeWhenDone: true)

uses free() to release the memory, which means that it must be allocated with malloc().

Other (shorter, but potentially less efficient) methods to create a hex representation of a Data value can be found at How to convert Data to hex string in swift.

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