ios - 如何将 UInt32 转换为 UInt8

Question

我需要快速将 UInt32 附加到 NSMutableData 对象。问题是，我不知道如何访问 int 中的特定字节。

这是我尝试过的:

extension NSMutableData {

  enum Endianness {
    case LittleEndian, BigEndian
  }

  func appendUInt32(myInt: UInt32, endianness: Endianness = .LittleEndian) {
    var bytes = UInt8[]()
    for i in 0..sizeof(UInt32) {
      switch endianness {
        case .LittleEndian:
          bytes.append(UInt8(myInt >> i))
        case .BigEndian:
          bytes.append(UInt8(myInt >> (sizeof(UInt32) - 1 - i)))
      }
    }
    self.appendBytes(bytes, length:bytes.count)
  }
}

这会引发编译器异常，我无法将其从 UInt32 转换为 UInt8。有没有一种简单的方法可以简单地访问 UInt32 中的一个字节？

编辑:从评论中总结最终解决方案:

extension NSMutableData {

  enum Endianness {
    case LittleEndian, BigEndian
  }

  func appendUInt32(myInt: UInt32, endianness: Endianness = .LittleEndian) {
    var bytes = UInt8[]()
    for i in 0..sizeof(UInt32) {
      switch endianness {
        case .LittleEndian:
          bytes.append(UInt8(myInt >> UInt32(i * 8) & UInt32(0xff)))
        case .BigEndian:
          bytes.append(UInt8(myInt >> UInt32((sizeof(UInt32) - 1 - i) * 8) & UInt32(0xff)))
      }
    }
    self.appendBytes(bytes, length:bytes.count)
  }
}

Answer 1

确保 >>> 运算符的两个操作数属于同一类型。我将它们设为 UInt32。

extension NSMutableData {

    enum Endianness {
        case LittleEndian, BigEndian
    }

    func appendUInt32(myInt: UInt32, endianness: Endianness = .LittleEndian) {
        var bytes = UInt8[]()
        for i in 0..sizeof(UInt32) {
            switch endianness {
            case .LittleEndian:
                bytes.append(UInt8(myInt >> UInt32(i)))
            case .BigEndian:
                bytes.append(UInt8(myInt >> UInt32((sizeof(UInt32) - 1 - i))))
            }
        }
        self.appendBytes(bytes, length:bytes.count)
    }
}