Convert bytes/UInt8 array to Int in Swift

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There are two problems:

  • Int is a 64-bit integer on 64-bit platforms, your input data
    has only 32-bit.
  • Int uses a little-endian representation on all current Swift platforms,
    your input is big-endian.

That being said the following would work:

let array : [UInt8] = [0, 0, 0, 0x0E]
var value : UInt32 = 0
let data = NSData(bytes: array, length: 4)
data.getBytes(&value, length: 4)
value = UInt32(bigEndian: value)

print(value) // 14

Or using Data in Swift 3:

let array : [UInt8] = [0, 0, 0, 0x0E]
let data = Data(bytes: array)
let value = UInt32(bigEndian: data.withUnsafeBytes { $0.pointee })

With some buffer pointer magic you can avoid the intermediate
copy to an NSData object (Swift 2):

let array : [UInt8] = [0, 0, 0, 0x0E]
var value = array.withUnsafeBufferPointer({ 
     UnsafePointer<UInt32>($0.baseAddress).memory
})
value = UInt32(bigEndian: value)

print(value) // 14

For a Swift 3 version of this approach, see ambientlight’s answer.

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