what is an enum?

[Peteroid]

Using VS C++.NET 2005 Express in clr:/pure syntax. I have this enum, defined
like so:

enum My_Enum
{
ENUM_0 = 0,
ENUM_1
} ;

My_Enum enum_var ;

I'm trying to save/load enum_var to/from a file using ostream/istream. But:

output << enum_var ; //ok
input >> enum_var ; //error

So I tried saving the 'int' value of the enum vaviable:

output << int(enum_var) ; // ok
input >> enum_var ; //error

and even this doesn't work:

output << int(enum_var) ; // ok

int value ;
input >> value ; // ok
enum_var = value ; // error, can't convert?!

Help!! : )

[==P==]

 

[Tamas Demjen]

int value ;
input >> value ; // ok
enum_var = value ; // error, can't convert?!

int doesn't convert to an enum. You have to cast it:

int value;
input >> value;
enum_var = static_cast<My_Enum>(value);

Tom

 

[Peteroid]

Hi Tom,

Thanks for the workaround! : )

[==P==]

int doesn't convert to an enum. You have to cast it:

int value;
input >> value;
enum_var = static_cast<My_Enum>(value);

Tom

 

[Peter Oliphant]

int doesn't convert to an enum. You have to cast it:

Thanx for the workaraound, which I'm using! : )

However, how you explain this quote form an msdn2 on-line page:

http://msdn2.microsoft.com/en-us/library/17z041d4.aspx

The enum type
ANSI 3.5.2.2 The integer type chosen to represent the values of an
enumeration type
A variable declared as enum is an int.

So either they better take down this page or an enum variable IS an 'int',
let alone not being able to convert it to one!

[==P==]

 

[Tamas Demjen]

Thanx for the workaraound, which I'm using! : )

It's not a workaround, that's the way of doing it.

However, how you explain this quote form an msdn2 on-line page:

http://msdn2.microsoft.com/en-us/library/17z041d4.aspx

The enum type
ANSI 3.5.2.2 The integer type chosen to represent the values of an
enumeration type
A variable declared as enum is an int.

An enum converts to an int, but an int doesn't convert to an enum
without at least a warning. Once you write your own operator>> for the
enum type, you can simply use that. It would be even better if enum
didn't convert to an int, then you couldn't mix things up accidentally.
I think if you're forced to do a cast, it's a kind of confirmation of
your intentions, telling the compiler that it's not an accident but
that's what you really want.

Tom

 

[Peteroid]

OK. But then how do you interpret this statement:

A variable declared as enum is an int.

Is this a falsehood? It certainly doesn't suggest what you've said, and it
is the ENTIRETY of the explanation on MSDN2 for the concept of 'enum
type'...

http://msdn2.microsoft.com/en-us/library/17z041d4.aspx

[==P==]