:
: If I have a 2 byte byte array, how do I test bits within the bytes to
: determine if they are on ?
:
: for example, I need to check if bit 0 and 6 are on in byte 1 and bit
: 0, 2 and 5 in byte 2.
:
: I think I "and" it with 0x01 and 0x0x40, but am not familiar with the
: syntax or how to get to this level. Thanks. Also, do you check for
: each one, or is there one value you use ? I problably need to do it
: both ways in another section.
:
: thanks.
: mark
Allow me to offer an example as an explanation (note: I'm counting bit
positions from right to left starting with 0 consistent with your example)
'-------------------------------------
Dim TestByte As Byte
Dim BitTest As Byte
Dim BitValue As Byte
Dim BitSet As Boolean
'Byte 5 = binary value 0000 0101
TestByte = 5
'We want to test to see if bits 1, 2, 3, or 4 are set
For bitPosition As Byte = 0 To 3
'First, we convert this to a power of 2
'2^0 = 1 = 0001
'2^1 = 2 = 0010
'2^2 = 4 = 0100
'2^3 = 8 = 1000
BitTest = CByte(2^bitPosition)
'See if the bit is set
BitValue = TestByte And BitTest
If BitValue > 0 Then
BitSet = True
Else
BitSet = False
End If
'Output the result
Console.WriteLine("Bit position " & BitPosition & _
" for Byte Value " & TestByte & _
" is 'On': " & BitSet)
Next
'-------------------------------------
The key statement here is BitValue = TestByte And BitTest. You can define
BitTest however you want. For example, you can use the power of 2 approach
above or you can define it directly. Whatever.
Also, this example tests for one bit at a time. If you wanted to test for
several bits all at once, you can. Just use a value with the bits you want
tested for turn on and see if the resulting And operation returns that
value. For example, if you wanted to know if the first two bits are set, you
could use
BitValue = TestByte And 3
If BitValue = 3 Then
BitSet = True
Else
BitSet = False
End If
HTH
Ralf
