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I have a byte array with 512 Elements and need to get and set a single bit of a byte in this array.

The operation must not change any other bits, only the specified one.

So if I have a byte like &B00110011 and would like to change the third bit to 1 it should be &B00110111.

Like this:

Dim myarray(511) as byte

myarray(3).2 = 1 ---> This would change the third bit (start counting at 0) of the third byte to 1

I know it should be easily possible using bit-masking but I don't have the time to try for days to get it working.

Thanks for help!!!

Jan

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2 Answers 2

Reset to default
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A simple way to do this is using shifts. If you want to set the Nth bit of a number to 1:

mask = 1 << n ' if n is 3, mask results in 00001000
bytevalue = bytevalue or mask

To set a bit as 0:

mask = 255 - (1 << n) ' if n is 3, mask results in 11110111
bytevalue = bytevalue and mask

In both examples, bytevalue is the byte in which you want to alter and mask is also a byte.

EDIT: To retrieve the state of a bit easily is a lot like setting a bit, Where IsSet is a boolean:

mask = 1 << n ' just as above
IsSet = (bytevalue and mask) <> 0
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3 Comments

Thanks, this sounds easy. And how to GET the state easily?
The function to get the state is not right. ... !=0 is not possible in vb.net. Using <> 0 returns -1 on a bit that is set. Would you please correct it.
@user831915: sorry, I don't work in VB at all anymore. I detest the language, but bitmasks and such are a fun subject to talk about.
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Why don't you use the BitArray class?

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1 Comment

You could, but the values are not single bit.

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