Bits

[Dhugal]

Hi,


Can someone explain to me how to perform bit Manipulation and comparison in VB.

I have used it in Delphi, but have never had to in VB until now...

I have an integer field in a DB that has certain bits set to specify certain criteria.

I need to be able to check bits, and set them...

[Geoff Gunson]

Hi

I am assuming that you allready know the basics of binary and hex.

So.....

To do a comparision to check if a single bit in a byte, int or what ever you can use the logical And operator with a bit mask.

To toggle a single bit with in a value you use the Or operator.

i.e. &H7F Or &H80 = &hFF or in other words

0111 1111
OR
1000 0000
=
1111 1111

HTH

Geoff

[kedaman]

Similary you can use these operators for bit manipulation: Xor or Eqv(to invert bits) And (to set bits to 0) Or (to set bits to 1) Not (to invert all bits) and imp (implication)
You can operate several bits at the same time, since the comparation is bitwise, for instance 11110 and 10101 is 10100.

[paulw]

Note that these operators will work with any numerical values, not just Hex representations... it will cast to an integer type before performing the comparison though so do not bother using fractional parts...

kedaman - What is Imp, never come across that before - looks evil (geddit?)

Cheers,

P.

[kedaman]

Imp.. hehe, nope probably not evil even if it sounds evil. But you probably don't need to use it, there was a thread a while back about the implication operator and it proved to be useful in some special cases
0 imp 0 = 1
0 imp 1 = 1
1 imp 0 = 0
1 imp 1 = 1
false implicates always true, it just skips the second operand, otherways it returns the second operand.