Convert bytes/UInt8 array to Int in Swift

Question

How to convert a 4-bytes array into the corresponding Int?

let array: [UInt8] ==> let value : Int 

Example:

Input:

\0\0\0\x0e 

Output:

14 

Some code I found on the internet that doesn't work:

let data = NSData(bytes: array, length: 4) data.getBytes(&size, length: 4) // the output to size is 184549376 

Answer 1

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.

Answer 2

In Swift 3 it is now a bit more wordy:

let array : [UInt8] = [0, 0, 0, 0x0E] let bigEndianValue = array.withUnsafeBufferPointer {          ($0.baseAddress!.withMemoryRebound(to: UInt32.self, capacity: 1) { $0 }) }.pointee let value = UInt32(bigEndian: bigEndianValue)