bitwise OR AND, etc.

[Travis]

I don't have too much experience with bitwise operations. Here is what
I'm trying to accomplish. I have enum say:

enum myEnum { BILL = 0, KATIE = 1, JOHN = 2 }

Then I have an int that represents some combination of that enum,
like:

int WhoIsAllowed = BILL | KATIE | JOHN;

Then I wanted to be able to check an instance against the
WhoIsAllowed. like:

int KnockingAtDoor = BILL;

How can I check to see if BILL is in fact on the WhoIsAllowed?

I thought something like

if (KnockingAtDoor & WhoIsAllowed) { // let him in }

but it doesn't seem to be working.

Thanks.

 

[Ian Collins]

I don't have too much experience with bitwise operations. Here is what
I'm trying to accomplish. I have enum say:

enum myEnum { BILL = 0, KATIE = 1, JOHN = 2 }

Then I have an int that represents some combination of that enum,
like:

int WhoIsAllowed = BILL | KATIE | JOHN;

Then I wanted to be able to check an instance against the
WhoIsAllowed. like:

int KnockingAtDoor = BILL;

How can I check to see if BILL is in fact on the WhoIsAllowed?

Change the enum so BILL has one bit set.

 

[Travis]

Change the enum so BILL has one bit set.

I'm sorry I'm not sure what you mean?

 

[Travis]

I'm sorry I'm not sure what you mean?

As in don't start with 0 so that every value has at least some bit
set? I'll try that. Thanks.

 

[Travis]

As in don't start with 0 so that every value has at least some bit
set? I'll try that. Thanks.

This brings up another question, is it possible to search for the
absence of someone. Like

pseudo
if Zack ISNOTIN WhoIsAllowed
{
Add zack to list
}

 

[Gianni Mariani]

I don't have too much experience with bitwise operations. Here is what
I'm trying to accomplish. I have enum say:

enum myEnum { BILL = 0, KATIE = 1, JOHN = 2 }

write this like so:

enum myEnum { BILL = 1<<0, KATIE = 1<<1, JOHN = 1<<2 };

 

[Ian Collins]

Travis wrote:

Please trim your quotes!

This brings up another question, is it possible to search for the
absence of someone. Like

pseudo
if Zack ISNOTIN WhoIsAllowed
{
Add zack to list
}

Yes, use bitwise and.

 

[Jim Langston]

This brings up another question, is it possible to search for the
absence of someone. Like

pseudo
if Zack ISNOTIN WhoIsAllowed
{
Add zack to list
}

Lets say Joe is 1 (1<<0)
Lets say Zack is 2 (1<<1)
Lets say Bill is 4 (1<<2)

Lets say WhoIsAllowed is
int WhoIsAllowed = Joe | Bill;

Now, you want to know if Zack is allowed.

if (WhoIsAllowed & Zack )
// allowed
else
// Not allowed

WhoIsAllowed & Zack will be equal to 0. 0 used as bool is false.
WhoIsAllowed & Joe will be equal to 1. Non zeros used as bool is true.
WhoIsAllowed & Bill will be equal to 4. Non zeros used as bool is true.

No make it easier to figure out what you are doing, I would probalby code
it:
if ( WhoIsAllowed & Zack == 0 )
// Not Allowed

But again, read my prevoius response about why Iwouldn't use enums for htis
typeof thing anyway and code that I would use.

 

[Travis]

Thanks but this way of smacking readable labels with enums makes much
more sense. I don't have a ton users it's more like GOD, ADMIN, REG
and that's it.

Thank you everyone for your help.