Check Bitwise flags

[Anil Gupte]

This is somethings I used to do often in other languages (such as Lisp), but
don't know how to do in VB.

I want to check if a certain bit (flag) is set. For example if I want to
check whether the 2nd bit is set, I compare it to binary 2

7 and 2 should return true (111 AND 010 = true)

How does one do this in VB?

Thanx,
--
Anil Gupte

https://www.keeninc.net

www.icinema.com

[Matthias Tacke]

Re: Check Bitwise flags

Anil Gupte wrote:

This is somethings I used to do often in other languages (such as Lisp), but
don't know how to do in VB.
>
I want to check if a certain bit (flag) is set. For example if I want to
check whether the 2nd bit is set, I compare it to binary 2
>
7 and 2 should return true (111 AND 010 = true)
>
How does one do this in VB?
>

The same way,

Sub Main()
Dim MyByte As Byte = &HAA
Dim I As Integer
WriteLine("Bit_ no :____8____7____ 6____5____4____ 3____2____1")
Write("Bitval :")
For I = 8 To 1 Step -1
Write((2 ^ (I - 1)).ToString.Pa dLeft(5))
Next
WriteLine()
Write("current: ")
For I = 8 To 1 Step -1
If MyByte And (2 ^ (I - 1)) Then
Write((2 ^ (I - 1)).ToString.Pa dLeft(5))
Else
Write(" 0")
End If
Next
Write(MyByte.To String.PadLeft( 5))
ReadLine()
End Sub

HTH
Matthias

[Heikki Leivo]

Re: Check Bitwise flags


"Anil Gupte" <anil-list@icinema.co mwrote in message
news:edzH%23g6Y HHA.4692@TK2MSF TNGP04.phx.gbl. ..

This is somethings I used to do often in other languages (such as Lisp),
but don't know how to do in VB.
>
I want to check if a certain bit (flag) is set. For example if I want to
check whether the 2nd bit is set, I compare it to binary 2
>
7 and 2 should return true (111 AND 010 = true)
>
How does one do this in VB?

You already gave the answer by yourself. I don't quite see why you need a
function to do this, but who cares. So:


Function CheckBitMask(Bi tmask As Long, Value As Long) As Boolean
Return CBool(Bitmask And Value)
End Function

Sub Foo()
'7 and 2 should return true (111 AND 010 = true)
Console.WriteLi ne(CheckBitMask (2, 7).ToString)
End Sub

[Herfried K. Wagner [MVP]]

Re: Check Bitwise flags

"Anil Gupte" <anil-list@icinema.co mschrieb:

This is somethings I used to do often in other languages (such as Lisp),
but don't know how to do in VB.
>
I want to check if a certain bit (flag) is set. For example if I want to
check whether the 2nd bit is set, I compare it to binary 2
>
7 and 2 should return true (111 AND 010 = true)

\\\
If CBool(Foo And &H2) Then
...
End If
///

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Anil Gupte]

Re: Check Bitwise flags

Thanx, I will check out both solutions (yours and Heikki's).

Regards,
--
Anil Gupte

https://www.keeninc.net

www.icinema.com

"Herfried K. Wagner [MVP]" <hirf-spam-me-here@gmx.atwrot e in message
news:O%23DL6o9Y HHA.4872@TK2MSF TNGP03.phx.gbl. ..

"Anil Gupte" <anil-list@icinema.co mschrieb:

>This is somethings I used to do often in other languages (such as Lisp),
>but don't know how to do in VB.
>>
>I want to check if a certain bit (flag) is set. For example if I want to
>check whether the 2nd bit is set, I compare it to binary 2
>>
>7 and 2 should return true (111 AND 010 = true)

>
\\\
If CBool(Foo And &H2) Then
...
End If
///
>
--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

[Anil Gupte]

Re: Check Bitwise flags

Funny! :-)

--
Anil Gupte

https://www.keeninc.net

www.icinema.com

"Matthias Tacke" <Matthias@Tacke .dewrote in message
news:et0gn0$953 $1@news.albasan i.net...

Anil Gupte wrote:

>This is somethings I used to do often in other languages (such as Lisp),
>but don't know how to do in VB.
>>
>I want to check if a certain bit (flag) is set. For example if I want to
>check whether the 2nd bit is set, I compare it to binary 2
>>
>7 and 2 should return true (111 AND 010 = true)
>>
>How does one do this in VB?
>>

>
The same way,
>
Sub Main()
Dim MyByte As Byte = &HAA
Dim I As Integer
WriteLine("Bit_ no :____8____7____ 6____5____4____ 3____2____1")
Write("Bitval :")
For I = 8 To 1 Step -1
Write((2 ^ (I - 1)).ToString.Pa dLeft(5))
Next
WriteLine()
Write("current: ")
For I = 8 To 1 Step -1
If MyByte And (2 ^ (I - 1)) Then
Write((2 ^ (I - 1)).ToString.Pa dLeft(5))
Else
Write(" 0")
End If
Next
Write(MyByte.To String.PadLeft( 5))
ReadLine()
End Sub
>
HTH
Matthias

[Heikki Leivo]

Re: Check Bitwise flags

Thanx, I will check out both solutions (yours and Heikki's).

Of course Herfrieds solution is the way to go, since there is no need to
wrap a logical operation such as foo And bar into a function. I realized
later that you didn't even ask for a function, just a solution. Sometimes a
solution is far too obvious to be seen directly.

-h-

[Mythran]

Re: Check Bitwise flags



"Herfried K. Wagner [MVP]" <hirf-spam-me-here@gmx.atwrot e in message
news:O#DL6o9YHH A.4872@TK2MSFTN GP03.phx.gbl...

"Anil Gupte" <anil-list@icinema.co mschrieb:

>This is somethings I used to do often in other languages (such as Lisp),
>but don't know how to do in VB.
>>
>I want to check if a certain bit (flag) is set. For example if I want to
>check whether the 2nd bit is set, I compare it to binary 2
>>
>7 and 2 should return true (111 AND 010 = true)

>
\\\
If CBool(Foo And &H2) Then
...
End If
///
>
--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>

Should it not be:

If Foo And &H2 = &H2
...
End If

?? Performing a bitwise AND will give a result of &H2 if &H2 is set to ON
and will give you 0 if &H2 is not set... Also, doing it this way, you don't
need to convert to boolean since adding "= &H2" makes it a boolean
expression...

HTH,
Mythran

[Heikki Leivo]

Re: Check Bitwise flags

Should it not be:

>
If Foo And &H2 = &H2

?? Performing a bitwise AND will give a result of &H2 if &H2 is set to ON
and will give you 0 if &H2 is not set... Also, doing it this way, you
don't need to convert to boolean since adding "= &H2" makes it a boolean
expression...

What else could Foo And &H2 be than 0 and &h2? I don't quite see your point,
there is only one bit set in &H2. In languages such as c/c++ there is no
need to cast something to boolean, since any nonzero value is defined to be
"true".

-h-

[Herfried K. Wagner [MVP]]

Re: Check Bitwise flags

"Heikki Leivo" <heikkidotleivo @cadworksdotfi. removethisschri eb:

>Should it not be:
>>
>If Foo And &H2 = &H2

>

>?? Performing a bitwise AND will give a result of &H2 if &H2 is set to
>ON and will give you 0 if &H2 is not set... Also, doing it this way, you
>don't need to convert to boolean since adding "= &H2" makes it a boolean
>expression.. .

>
What else could Foo And &H2 be than 0 and &h2? I don't quite see your
point, there is only one bit set in &H2.

'CBool' will return 'True' if a bit in the value passed to it is set to 1.

In languages such as c/c++ there is no need to cast something to boolean,
since any nonzero value is defined to be "true".

Such automatic conversions are performed with 'Option Strict Off', but I
think that the more explicit way is the better choice
most times.

--
M S Herfried K. Wagner
M V P <URL:http://dotnet.mvps.org/>
V B <URL:http://dotnet.mvps.org/dotnet/faqs/>