Beginner: Using Bitflags

[Matthias S.]

Hi,

I've got a class with an Options property. I'd like to implement this
property in a way that a calling syntax like

MyClassInstance.Options = MyClass.Option1 | MyClass.Option2;

can be used. My questions with that:

1. How do I store these BitFlags internally?
2. How do I check for whether certain Bits have been set.
3. The above code shows how to switch 2 bits ON (hopefully, correct me
if I'm wrong). How would the syntax look If I'd like to switch Option1
ON and Option2 OFF?

I'd highly appreceate a short example!

Thanks in advance.

Matthias

[Mike Newton]

Try using enumerations with the FlagsAttribute class.

If Option1 and Option2 were bits, then your assumption in 3 is
incorrect. The code performs an OR on the bits, so MyClass.Options will
tell you that at least one of the is on.

This shows an example of how to use them.
http://msdn.microsoft.com/library/de...classtopic.asp

Matthias S. wrote:

Hi,

I've got a class with an Options property. I'd like to implement this
property in a way that a calling syntax like

MyClassInstance.Options = MyClass.Option1 | MyClass.Option2;

can be used. My questions with that:

1. How do I store these BitFlags internally?
2. How do I check for whether certain Bits have been set.
3. The above code shows how to switch 2 bits ON (hopefully, correct me
if I'm wrong). How would the syntax look If I'd like to switch Option1
ON and Option2 OFF?

I'd highly appreceate a short example!

Thanks in advance.

Matthias

[Drebin]

Here's a simple way to do something like this:

const int Red = 1;
const int Green = 2;
const int Blue = 4;
const int Yellow = 8;

int intMyOptions = 0;
MessageBox.Show("Start: " + intMyOptions.ToString());

intMyOptions = (intMyOptions | Red);
MessageBox.Show("Options after first red: " + intMyOptions.ToString());

// Once bit is set, it won't unset or append
intMyOptions = (intMyOptions | Red);
MessageBox.Show("Options after second red: " + intMyOptions.ToString());

intMyOptions = (intMyOptions | Yellow);
MessageBox.Show("Options after yellow: " + intMyOptions.ToString());

string strResults = "Results:\n\n";
strResults += "Red: " + (((intMyOptions & Red) > 0)? "Y" : "N") + "\n";
strResults += "Green: " + (((intMyOptions & Green) > 0)? "Y" : "N") + "\n";
strResults += "Blue: " + (((intMyOptions & Blue) > 0)? "Y" : "N") + "\n";
strResults += "Yellow: " + (((intMyOptions & Yellow) > 0)? "Y" : "N") +
"\n";
MessageBox.Show(strResults);

"Matthias S." <po*****@emvoidSPAMTRAP.de> wrote in message
news:%2***************@TK2MSFTNGP10.phx.gbl...

Hi,

I've got a class with an Options property. I'd like to implement this
property in a way that a calling syntax like

MyClassInstance.Options = MyClass.Option1 | MyClass.Option2;

can be used. My questions with that:

1. How do I store these BitFlags internally?
2. How do I check for whether certain Bits have been set.
3. The above code shows how to switch 2 bits ON (hopefully, correct me
if I'm wrong). How would the syntax look If I'd like to switch Option1
ON and Option2 OFF?

I'd highly appreceate a short example!

Thanks in advance.

Matthias

[Richard Blewett [DevelopMentor]]

The standard way is to use an enumeration with the values explicitly set so the binary representations of 0 - 8 are as follows.

0 0000

1 0001

2 0010

4 0100

8 1000

as you can see eac one sets a different bit so you can always tell which ones were selected

so declare an enum:

enum Commitment

{

Heart = 1,

Mind = 2,

Soul = 4

}

Then you can write

Commitment c = Commitment.Heart | Commitment.Soul;

Now its good practice (though not required) to decorate the enum with the

[System.Flags]

attribute. This does two things: it signals to users of the enum that it is intended to me used as a set of bitfields; it changes the way ToStriing works so it prints out a comma separated list of the combined symbols. By default enums occupy 32 bits of storage (so you can have 32 bitwise or-able values). However, you can change this storage type as follows

enum Commitment : byte // any integral type will do fine here

{

...

}

Even though it looks like derivation from a value type (which isn't supported in .NET) it simply states the underlying storage for the enum type.

Regards

Richard Blewett - DevelopMentor

http://staff.develop.com/richardrb/weblog

nntp://news.microsoft.com/microsoft.public.dotnet.languages.csharp/<#u*************@TK2MSFTNGP10.phx.gbl>

Hi,

I've got a class with an Options property. I'd like to implement this
property in a way that a calling syntax like

MyClassInstance.Options = MyClass.Option1 | MyClass.Option2;

can be used. My questions with that:

1. How do I store these BitFlags internally?
2. How do I check for whether certain Bits have been set.
3. The above code shows how to switch 2 bits ON (hopefully, correct me
if I'm wrong). How would the syntax look If I'd like to switch Option1
ON and Option2 OFF?

I'd highly appreceate a short example!

Thanks in advance.

Matthias

[microsoft.public.dotnet.languages.csharp]