Trouble reading bits.

Trouble reading bits.

• jreed

   

  Remember I was saying were going to demonstrate how to set bit 3.

  in binary, setting bit 3 would look like 00001000   = 8.

  ByteEntity means any byte

  If Mask = 8, bit three is set.   Mask Logically ORed with any byte or byteenity would insure that bit 3 is set.

  8. Logically ORed with any byte will insure that bit three is set.

  
  
  

• TravisQuerec

  Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
  
  Dim buffer(bytecount) As Byte
  Dim word As String
  
  For i As Byte = 0 To 7
  
  If TestByteBits(67248, buffer, i) Then word = "" Else word = "not "
  
  MsgBox("With a decimal value of " & buffer(67248) & " in byte number " & 67248 & vbCrLf & _
  "bit number " & i & " is " & word & "set.", MsgBoxStyle.Information, word & "set")
  
  Next
  
  End Sub
  
  
  
  
  
  Private Function TestByteBits(ByVal Offset As Integer, ByRef Buffer As Byte(), ByVal BitNo As Integer) As Boolean
  
  'if Bitno exceeds 7 - declare the caller has made an error. (for you to impliment)
  
  Dim mask As Byte = 1 << BitNo
  
  If ((Buffer(Offset) And mask) <> 0) Then Return True
  
  Return False
  
  End Function
  
  Ok so that it what I used of your code. but for some reason I says that the deciaml value is 0 when it is not. Maybe it's not using the buffer All my other function display all their values correctly from the buffer. Also thanks for adding in the MsgBox. It made it so much easier to understand.
  
  
  

• Sohailsoh

  Ok. I figured out how to write the seperate bits back to the buffer. I got this:
  
  If cSkill_3.Checked = True Then Buffer.SetByte(b, 67247, 1 << 2)
  If cSkill_6.Checked = True Then Buffer.SetByte(b, 67247, 1 << 5)
  WriteBytes(b, tbCurrentFile.Text)
  
  I went through the help files and found out what << was used for. The above code is probably completely inefficient, though. Now my problem is even if both the statements are true (both boxes checked) It only changes bit 6. So, I get a value of 20h instead of 24h. I figure I need to maybe add the two statements together somehow, although I have not figured out how to accomplish such a task. Those boolean operators give me a headache. Any ideas
  
  
  

• Mario Chenier - Microsoft

  I wouldn't do it that way....

  I'd copy the byte out of memory and play with it

  If I modify it and want to put it back then copy the byte back to memory as a byte.

  "<>" is a boolean it mean "Not equals to"

  the &H1 is called a constant it can be declared in a number of ways

  const mybyte as byte = &h22B

  makes a byte constant Note the "B" after the quotation

  But anyway... here's is something to play with...

  Public Class Form1

  Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

  Dim buffer(300) As Byte

  Dim b As Boolean = TestByteBits(5, buffer, 1, 0)

  End Sub

  Private Function TestByteBits(ByVal Offset As Integer, ByRef Buffer As Byte(), _

  ByVal Byteno As Integer, ByVal BitNo As Integer) As Boolean

  'if Bitno exceeds 7 - declare the caller has made an error. (for you to impliment)

  Dim mask As Byte = 1 << BitNo

  If Buffer(Offset) And mask <> 0 Then Return True

  Return False

  End Function

  End Class

  
  
  

• Matthew Petersen

   

  In your example, I can't see where bytecount is defined......

   

  and if this code:

  MsgBox("With a decimal value of " & buffer(67248) & " in byte .......

  says the value is zero...... I'd count on it being zero.

  
  
  

• apedrosa

  It pretty clear why it doesn't work

  I've also recommended what you should be doing in relation to memory. You've chose not to follow those recommendations but you've made errors that expeience has taugh me can happened.

  First of the << and >> operators DO NOT set bits. they Shift all the bits in a byte or short or integer.

  So what you did was a guranteed memory corruptor.

  How do you set a bit in byte

  lets say you want to set bit 3 in a byte.

  Mask = 8 ' Mask is a byte

  if you have a known mask you can Logically OR the mask to the byte

  ByteEntity= ByteEntity OR Mask

  Bit 3 has been set

  
  
  

• Scott Weinstein

  I was playing around with that code you wrote and no matter what the value of the offset the function always returns false.
  
  I got it set to display the output in a textbox.
  
  And I don't understand all of the arguments you used. Offset is the address and Buffer is the buffer and bitno is the bit but what would byteno be
  
  Does If Buffer(Offset) And mask <> 0 mean if the offset and the mask are both equal to zero
  
  This seems alot harder than it should be. Or maybe I am just not understanding it.
  
  
  

• BlackZombie

  Sorry about being so vague. I'm not using bytecount anymore. The reason it kept coming out zero was because the buffer I was using wasn't defined. I got this instead:
  
  For i As Byte = 0 To 7
  
  If TestByteBits(67247, b, 0) Then cSkill_1.Checked = True Else cSkill_1.Checked = False
  If TestByteBits(67247, b, 1) Then cSkill_2.Checked = True Else cSkill_2.Checked = False
  If TestByteBits(67247, b, 2) Then cSkill_3.Checked = True Else cSkill_3.Checked = False
  If TestByteBits(67247, b, 3) Then cSkill_4.Checked = True Else cSkill_4.Checked = False
  If TestByteBits(67247, b, 4) Then cSkill_5.Checked = True Else cSkill_5.Checked = False
  If TestByteBits(67247, b, 5) Then cSkill_6.Checked = True Else cSkill_6.Checked = False
  
  Next
  
  (I only need the first 6 bits)
  
  I got it to work though and am currently trying to figure out how to write the bits back to the buffer.
  Thanks.
  
  
  

• jbog91

   

   

  Well that’s what I get for writing code at 4:00 AM. <blush>.

   

  There was an extra unused argument… AND there was an error – not in the logic but there was a precidence error in the IF statement. I didn’t change my logic, I just added some parentheses. This does work, Troy.

   

   

  Public Class Form1

   

      Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

          Dim buffer(300) As Byte

          Const offset As Integer = 5

          Dim word As String

          buffer(offset) = 23

   

          For i As Byte = 0 To 7

   

              If TestByteBits(offset, buffer, i) Then word = "" Else word = "not"

   

              MsgBox("With a decimal value of " & buffer(offset) & " in byte number " & offset & vbCrLf & _

              "bit number " & i & " is " & word & " set.", MsgBoxStyle.Information, word & " set")

   

          Next

   

      End Sub

   

   

      Private Function TestByteBits(ByVal Offset As Integer, ByRef Buffer As Byte(), ByVal BitNo As Integer) As Boolean

          'if Bitno exceeds 7 - declare the caller has made an error. (for you to impliment)

   

          Dim mask As Byte = 1 << BitNo

          If ((Buffer(Offset) And mask) <> 0) Then Return True

          Return False

      End Function

  End Class

  Does If Buffer(Offset) And mask <> 0 mean if the offset and the mask are both equal to zero
  

  No, it doesn't. It means if the result of the Logical AND of the byte and the Mask is non-zero then the bit is set. A Logical AND sets bits that are set in both entities, so if bit 1 of both the mask and the byte were set, their Logical AND would be non-zero.

  Good luck.

   

   

  
  
  

• xiaoyifang

  ok...
  
  So how am I corrupting memory And, which method should I use if not this one
  I figured if I used the shift operator to extract the bits then I could use it to insert them as well.
  Hmm...This is pretty much the only part of my program that does not work.
  
  
  

• amiller099

  It was clear to you, not me. I don't know what this stuff means. That is why I am asking.
  
  Now here are my novice questions:
  
  Why does Mask = 8.
  What is ByteEntity
  Which part of ByteEntity = ByteEntity OR Mask represents bit 3
  
  Wait, wait, wait...Let me see if I can explain what I am trying to do. I have 8 checkboxes. I want each one to represent a different bit (0-7). When I check box1 then I want bit 0 to equal true, and so on. If I could have this process explained to me then my question will be answered.
  
  Remember, I don't know every expression or method in BASIC, or even most of them. If I did then I wouldn't be here.
  
  Thanks.
  
  
  

• JustBitsNBytes

  Ok so I now have:
  
  If (CDec(b(67248)) And &H1 <> 1) Then
  cSkill_1.Checked = True
  End If
  
  Here are some things that I don't understand. My code editor says that &H1 is an integer, but what is it exactly It says that <> is boolean, but I have never seen that symbol in my searches, so what does it mean Also would the above example mean: if bit 1 at address 67248 is true, or am I totally off I think &H mean it's hex, right Ah, I am confused. I want if a certain bit is true then to check a checkbox. So, am I right Thanks again.
  
  
  

• Gertus

  No.

  You're not setting a bit. You're corrupting memory that way.

  
  
  

• Steve Landis

  Read the byte as a byte and then inspect individual bits

  Here's how to test bit 0

  if byte and &h1 <> 0 then

  endif

  Remember troy... just read and write bytes to a bytes array.

  Do your other processing in the interim.

  
  
  
• Trouble reading bits.