C# integer masking into byte array

Question

I'm confused as to why this isn't working, can someone please provide some insight?

I have a function who is taking in an integer value, but would like to store the upper two bits of the hex value into a byte array element.

Let's say if Distance is (24,135)₁₀ or (5E47)₁₆

public ConfigureReportOptionsMessageData(int Distance, int DistanceCheckTime)
    {
        ...
        this._data = new byte[9];
        this._data[0] = (byte)(Distance & 0x00FF); // shows 47
        this._data[1] = (byte)(Distance & 0xFF00); // shows 00
        this._data[2] = (byte)(DistanceCheckTime & 0xFF);
        ...
    }

BTW - what are you doing with the other 2 bytes in Distance? — Reed Copsey
– Reed Copsey, Commented Nov 4, 2010 at 0:13
@Reed Copsey: Nothing, there was a maximum set. If it was meters, the limit was 30,000. — mastofact
– mastofact, Commented Nov 4, 2010 at 0:18

Vlad · Accepted Answer · 2010-11-04 00:09:05Z

2

this._data[1] = (byte)(Distance >> 8);

?

answered Nov 4, 2010 at 0:09

Vlad

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1 Comment

codekaizen Over a year ago

(byte)(Distance >> 8), not (byte)(Distance >> 16)

Reed Copsey · Accepted Answer · 2010-11-04 00:08:48Z

2

This seems like you should be using BitConverter.GetBytes - it will provide a much simpler option.

answered Nov 4, 2010 at 0:08

Reed Copsey

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4 Comments

codekaizen Over a year ago

I think he heeds a 9 byte array. BitConverter.GetBytes would then need an Array.Copy or Buffer.Copy.

Reed Copsey Over a year ago

@codekaizen: Yeah, but I'd still say it's more maintainable, since it's obvious what's being done.

codekaizen Over a year ago

I somewhat disagree. After writing and maintaining a binary protocol handler, using BitConverter is less easy to maintain. Surprised me, too.

Reed Copsey Over a year ago

@codekaizen: Yeah - depends on how your data stream is coming into the routine. In this case, converting from int to byte - I'd prefer to maintain somebody's code using BitConverter than bitshifting - especially given that it's going into a single large array. Intent is easier to follow.

codekaizen · Accepted Answer · 2010-11-04 00:14:03Z

1

The reason you get 0 for _data[1] is that the upper 3 bytes are lost when you cast to byte.

Your intermediate result looks like this:

Distance && 0xff00 = 0x00005e00;

When this is converted to a byte, you only retain the low order byte:

(byte)0x00005e00 = 0x00;

You need to shift by 8 bits:

0x00005e00 >> 8 = 0x0000005e;

before you cast to byte and assign to _data[1]

answered Nov 4, 2010 at 0:14

codekaizen

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