Convert a ushort value into two byte values in C#

Question

How do I split a ushort into two byte variables in C#?

I tried the following (package.FrameID is ushort):

When I try to calculate this with paper&pencil I get the right result. Also, if FrameID is larger than a byte (so the second byte isn't zero), it works.

array[0] = (byte)(0x0000000011111111 & package.FrameID);
array[1] = (byte)(package.FrameID >> 8);

In my case package.FrameID is 56 and the result in array[0] is 16 instead of 56.

How can I fix this?

Solution 1

0x0000000011111111 is not a binary number, it's a hex number. You need to use 0x0ff instead.

However, since the result is a byte and casting to a byte will discard the upper bits anyway, you don't actually need to and the result. You can just do this:

array[0] = (byte)package.FrameID;
array[1] = (byte)(package.FrameID >> 8);

(That's assuming that you are not using checked code. If you are, then casting a value greater than 255 to a byte will cause an exception. You will know if you are using checked code.)

Solution 2

Use BitConverter

var bytes = BitConverter.GetBytes(package.FrameID);

Comments

[user2071938]

Thanks alot! But any Idea whats the problem with my solution?

[EZI]

@user2071938 0x0000000011111111 is a 8-byte hex number. They are not bits as you think. it should be 0x00ff

[King King]

@user2071938 1 hex digit stands for 4 bits, so 1 byte will correspond to 2 hex digits.

[King King]

0x0f is 1 byte, if we perform a bit and operation on it and the ushort, the return value is only the lower-nibble of the lower byte, I think it's 0x00ff.

[Matthew Watson]

@KingKing Thanks, fixed the typo

[Jeppe Stig Nielsen]

This is the best solution. Regarding the constant 0x0000000011111111, it seems to be an 8-byte number (16 hex digits), but since the leading 8 hex digits are all zero, it is interpreted as a 4-byte number. And since the first non-zero digit (1) is between 1 and 7, not between 8 and f, this is an int, not a uint. You can try var a = 0x11223344; (int), var b = 0x81223344; (uint), var c = 0x112233448899aabb; (long), var d = 0x812233448899aabb; (ulong).

[Lonefish]

You could also use 0x0000000011111111 if you wanted to use the binary number (notice leading 0b instead of 0x)