swift3でswift2.3で動いていたC構造体メンバ（Char配列）を読み込むコードが動かなかった件について

 #define MEM01_SIZE 255
 struct cstruct {
    char cstr01[MEM01_SIZE];
  } 

var size: Int32 = 0
var cstruct = GetCStruct(&size)
let cstr01_str = withUnsafePointer(&cstruct.memory.cstr01)
{
 return String.fromCString(UnsafePointer($0))!
}

var cstr01_str_tuple = cstruct?.pointee.cstr01
let cstr01_str = withUnsafePointer(to: &cstr01_str_tuple)
{
  return String(cString: UnsafeRawPointer($0).assumingMemoryBound(to: CChar.self))
}