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Split UInt32 into [UInt8] in swift

I want to add UInt32

to the buffer the byte I am using [UInt8]

. There is a convenient ByteBuffer class in java that has methods like putInt () for cases in exactly the same way. How can this be done quickly?

I think I could solve it like this:

let example: UInt32 = 72 << 24 | 66 << 16 | 1 << 8 | 15
var byteArray = [UInt8](count: 4, repeatedValue: 0)

for i in 0...3 {
    byteArray[i] = UInt8(0x0000FF & example >> UInt32((3 - i) * 8))
}

Is this a rather verbose, albeit easier way?

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5 answers


Your loop is more compactly written as

let byteArray = 24.stride(through: 0, by: -8).map {
    UInt8(truncatingBitPattern: example >> UInt32($0))
}

Alternatively, create UnsafeBufferPointer

and convert this to an array:



let example: UInt32 = 72 << 24 | 66 << 16 | 1 << 8 | 15

var bigEndian = example.bigEndian
let bytePtr = withUnsafePointer(&bigEndian) {
    UnsafeBufferPointer<UInt8>(start: UnsafePointer($0), count: sizeofValue(bigEndian))
}
let byteArray = Array(bytePtr)

print(byteArray) // [72, 66, 1, 15]

Update for Swift 3 (Xcode 8 beta 6):

var bigEndian = example.bigEndian
let count = MemoryLayout<UInt32>.size
let bytePtr = withUnsafePointer(to: &bigEndian) {
    $0.withMemoryRebound(to: UInt8.self, capacity: count) {
        UnsafeBufferPointer(start: $0, count: count)
    }
}
let byteArray = Array(bytePtr)
+8


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You can use one UnsafeMutablePointer type for another:



var arr = UnsafeMutablePointer<UInt32>.alloc(1)
arr.memory = example
var arr2 = UnsafeMutablePointer<UInt8>(arr)
+3


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Improved @ Martin R's answer. Worked on UInt16, UInt32 and UInt64:

protocol UIntToBytesConvertable {
    var toBytes: [Byte] { get }
}

extension UIntToBytesConvertable {
    func toByteArr<T: Integer>(endian: T, count: Int) -> [Byte] {
        var _endian = endian
        let bytePtr = withUnsafePointer(to: &_endian) {
            $0.withMemoryRebound(to: Byte.self, capacity: count) {
                UnsafeBufferPointer(start: $0, count: count)
            }
        }
        return [Byte](bytePtr)
    }
}

extension UInt16: UIntToBytesConvertable {
    var toBytes: [Byte] {
        return toByteArr(endian: self.littleEndian,
                         count: MemoryLayout<UInt16>.size)
    }
}

extension UInt32: UIntToBytesConvertable {
    var toBytes: [Byte] {
        return toByteArr(endian: self.littleEndian,
                         count: MemoryLayout<UInt32>.size)
    }
}

extension UInt64: UIntToBytesConvertable {
    var toBytes: [Byte] {
        return toByteArr(endian: self.littleEndian,
                         count: MemoryLayout<UInt64>.size)
    }
}
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I have a similar problem with Xcode 8 Beta 6: write this line

var value = String(cString: sqlite3_column_text(stmt, index))

   to


let txt = UnsafePointer<Int8>(sqlite3_column_text(stmt, index))

and solve problems

0


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Improved @ Martin R's answer.

func toByteArrary<T>(value: T)  -> [UInt8] where T: UnsignedInteger, T: FixedWidthInteger{
  var bigEndian = value.bigEndian
  let count = MemoryLayout<T>.size
  let bytePtr = withUnsafePointer(to: &bigEndian) {
    $0.withMemoryRebound(to: UInt8.self, capacity: count) {
        UnsafeBufferPointer(start: $0, count: count)
    }
  }

  return Array(bytePtr)
}
0


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