Using the OR | w/ an enum

[Travis]

So I have been doing C++ for quite awhile but have never had too many
occasions to use |.

What I'm trying to provide is ability to say enum myEnum = myEnum::one
| myEnum::two.

I'm not sure if this makes sense so I'll use my actual situation as an
example.

I am doing a menu system where each button the screen has an access
role as does the user. So the simplest example would be.

User is Susie;

Button 1 should be available to Susie or Johnny.

So Button1.Access = myEnum::Susie | myEnum::Johnny.

Is that the best way to do it? Is it even possible? Thanks for the
help.

[Travis]

On Sep 14, 10:07 am, Travis <travis.bow...@ gmail.comwrote:

So I have been doing C++ for quite awhile but have never had too many
occasions to use |.

What I'm trying to provide is ability to say enum myEnum = myEnum::one
| myEnum::two.

I'm not sure if this makes sense so I'll use my actual situation as an
example.

I am doing a menu system where each button the screen has an access
role as does the user. So the simplest example would be.

User is Susie;

Button 1 should be available to Susie or Johnny.

So Button1.Access = myEnum::Susie | myEnum::Johnny.

Is that the best way to do it? Is it even possible? Thanks for the
help.

Oh I forgot to add that I got this idea that using | might work
because I didn't want to have to go through and do all the different
combinations like myEnum::Susie, myEnum::Johnny,
myEnum::JohnnyA NDSusie, etc.

[Victor Bazarov]

Travis wrote:

On Sep 14, 10:07 am, Travis <travis.bow...@ gmail.comwrote:

>So I have been doing C++ for quite awhile but have never had too many
occasions to use |.

What I'm trying to provide is ability to say enum myEnum =
myEnum::one

>>myEnum::two .

In most cases you cannot do that (nor do you really want to). If you
think that the inclusive-or combination of those two values should
also be a valid value in your 'myEnum', add it there *explicitly* in
the definition of the 'myEnum' enumeration.

>I'm not sure if this makes sense so I'll use my actual situation as
an example.

I am doing a menu system where each button the screen has an access
role as does the user. So the simplest example would be.

User is Susie;

Button 1 should be available to Susie or Johnny.

So Button1.Access = myEnum::Susie | myEnum::Johnny.

Is that the best way to do it? Is it even possible? Thanks for the
help.

Oh I forgot to add that I got this idea that using | might work
because I didn't want to have to go through and do all the different
combinations like myEnum::Susie, myEnum::Johnny,
myEnum::JohnnyA NDSusie, etc.

It would work if you don't try to make 'Button1.Access ' of the type
'myEnum'. It should be of type 'int' or 'unsigned' (or some such)
and when you need to check if 'Johnny' has access you would also do
the 'and' operation:

myEnum john_smith = Johnny; //
...
if (john_smith & Button1.Access) // Does 'john_smith' have access?
...

V
--
Please remove capital 'A's when replying by e-mail
I do not respond to top-posted replies, please don't ask

[James Kanze]

On Sep 14, 7:07 pm, Travis <travis.bow...@ gmail.comwrote:

So I have been doing C++ for quite awhile but have never had too many
occasions to use |.

What I'm trying to provide is ability to say enum myEnum = myEnum::one
| myEnum::two.

I'm not sure if this makes sense so I'll use my actual situation as an
example.

I am doing a menu system where each button the screen has an access
role as does the user. So the simplest example would be.

User is Susie;

Button 1 should be available to Susie or Johnny.

So Button1.Access = myEnum::Susie | myEnum::Johnny.

Is that the best way to do it? Is it even possible?

You have to define the enum values as bit masks, e.g.:

enum E
{
Susie = 0x01,
Johnny = 0x02,
// ...
} ;

You can then overload the | and the |= operators:

E
operator|( E lhs, E rhs )
{
return static_cast< E >(
static_cast< unsigned >( lhs )
| static_cast< unsigned >( rhs ) ) ;
}

E operator|=( E& lhs, E rhs )
{
lhs = lhs | rhs ;
}

If you do this, you may want to add an enum value none = 0,
since you can't pass 0 as an argument to a function expecting an
E. (Note that this sort of thing is a very frequent use of
enums in C++.)

--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]

[James Kanze]

On Sep 14, 7:15 pm, "Victor Bazarov" <v.Abaza...@com Acast.netwrote:

Travis wrote:

On Sep 14, 10:07 am, Travis <travis.bow...@ gmail.comwrote:

So I have been doing C++ for quite awhile but have never had too many
occasions to use |.

What I'm trying to provide is ability to say enum myEnum =
myEnum::one
myEnum::two.

In most cases you cannot do that (nor do you really want to).

Nonsense. The standard does it in many cases: ios::state, for
example.

If you think that the inclusive-or combination of those two
values should also be a valid value in your 'myEnum', add it
there *explicitly* in the definition of the 'myEnum'
enumeration.

That's not always reasonable, if the number of cases is large.

[...]

Oh I forgot to add that I got this idea that using | might work
because I didn't want to have to go through and do all the different
combinations like myEnum::Susie, myEnum::Johnny,
myEnum::JohnnyA NDSusie, etc.

It would work if you don't try to make 'Button1.Access ' of the
type 'myEnum'.

It works very well if Button1.Access has an enumerated type as
well. I do it all the time.

It should be of type 'int' or 'unsigned' (or some such)
and when you need to check if 'Johnny' has access you would also do
the 'and' operation:

myEnum john_smith = Johnny; //
...
if (john_smith & Button1.Access) // Does 'john_smith' have access?
...

You can apply the built-in | or & directly to the enum type, but
the results will have the underlying integral type (and that
should be:
if ( (john_smith & Button1.Access) != 0 )
unless you're into obfuscation). But since enum's are user
defined types, you can also overload the |, & and ~ operators
for them, to get the correct types. (Another alternative would
be to overload + and -, to add or remove an element, and use a
function contains() to test whether the enum contained the
element.)

Despite their name, enum, in C++, is not necessarily an
enumerated type, in the classical sense. It can be used as
such, but it can also be used as a small set of named elements.
Such use is very idiomatic C++.

--
James Kanze (GABI Software) email:ja******* **@gmail.com
Conseils en informatique orientée objet/
Beratung in objektorientier ter Datenverarbeitu ng
9 place Sémard, 78210 St.-Cyr-l'École, France, [phone]