c# - 以小端方式将整数转换为字节数组(通用函数)

Question

我有这种方法可以将长字节数组转换为小端字节数组

public static byte[] UnsignedIntegerToLEByteArray(ulong value)
{    
    // Value in bytes... in your system's endianness (let's say: little endian)
    byte[] bytes = BitConverter.GetBytes(value);

    // If it was big endian, reverse it
    if (!BitConverter.IsLittleEndian)
        Array.Reverse(bytes); 

    return bytes;
}

我的目标是也将它用于短数据类型，如 int、short 等。请参见此处:

byte a = 0xAA;
ushort b = 0xEEAA;
uint c = 0xAABBCCDD;
ulong d = 0xAABBCCDDAAAAAABB;
// If you passed short below, you are only interested
// in first two bytes of the array
byte []tmp = DppUtilities.UnsignedIntegerToLEByteArray(b);

如果我的机器是小端字节序，这会起作用。如果它在大端机器上运行它也会工作吗？我想是的，但我想验证一下。

Answer 1

你可以在 IntPtr 和 Marshal 的帮助下玩一个trick 来转换任何struct (包括byte, ushort 和ulong):

// Disclaimer: the structure will be reversed as a whole, not field by field
public static byte[] ToLEByteArray<T>(T value) where T: struct {
  int size = Marshal.SizeOf(typeof(T));
  byte[] bytes = new byte[size];

  IntPtr p = Marshal.AllocHGlobal(size);

  try {
    Marshal.StructureToPtr(value, p, true);
    Marshal.Copy(p, bytes, 0, size);
  }
  finally {
    Marshal.FreeHGlobal(p);
  }

  // If it was big endian, reverse it
  if (!BitConverter.IsLittleEndian)
    Array.Reverse(bytes);

  return bytes;
}

....

  Byte b = 123;
  ushort s = 123;
  ulong l = 123;

  Byte[] result_byte = ToLEByteArray(b);
  Byte[] result_ushort = ToLEByteArray(s);
  Byte[] result_ulong = ToLEByteArray(l);

....

  int i = 123456; 
  Byte[] result_int = ToLEByteArray(i);

编辑:问题中的实现有什么问题？ (来自评论)。 或者，重申一下这个问题，IntPtr、Marshal 的作用是什么？

问题实现的主要问题是初始转换到ulong:

  // all the arguments will be converted to ulong 
  public static byte[] UnsignedIntegerToLEByteArray(ulong value)

为了说明问题，想象一下，我们有两个值

Byte  x = 0x12;               // 18
ulong u = 0x0000000000000012; // 18

预期的输出是

new byte[] {0x12};                      // for a single byte
new byte[] {0x12, 0, 0, 0, 0, 0, 0, 0}; // for 8 bytes, i.e. ulong 

然而，实际输出将是

new byte[] {0x12, 0, 0, 0, 0, 0, 0, 0};

对于 byte 和 ulong。如果您想要将数值(byte、short、ulong 等)写到一个二进制文件，将它们传递给二进制流等:

  using (Stream stm = ...) {
    ...
    Byte[] buffer = UnsignedIntegerToLEByteArray(...);

    stm.Write(buffer, offset, buffer.Length); // <- the (possibly!) erroneous write
    ...
  }