Data 到 C数组

• 新的方法

 let data = "foo".data(using: .utf8)!
 let buff = [UInt8](data)

• 老的方法

 let data = "foo".data(using: .utf8)!
 let array = data.withUnsafeBytes{
         ([UInt8](UnsafeMutablePointer)(start: $0, cout: data.count))
      }