Strings ints and enums

[Jeremy]

Hello all,

I'm having some problems working with enumerations. A function call to
a 3rd party dll has in it's parameter list an enumerated type which
connects me to a COM port. I'm trying to convert a stored parameter
from a database into this enumerated value and can't seem to get
anything to work. In some VB.NET code that was written, it works fine
and that's the frustrating part. I've included some code below:

Old vb.net code to get the enumerated value from a string:

myEnum = [Enum].Parse(GetType( EnumType), "Enum Member")

This code works fine, unfortunatly VB has no problems converting from
an Object to EnumType. When I try the same thing in VC++ with:

myEnum = Enum::Parse(__t ypeof(EnumType) , "Enum Member");

I get the compiler error C2440: Cannot convert from 'Object *' to
'EnumType'. I've also tried several ways of casting and had no luck
with that either, so what I've had to resort is below:

String *myItem = "Enum member;
EnumType myEnum;

if (myItem->Equals(__box(E numType::Even)->ToString()))
theParity = EnumType::Even;
else if (myItem->Equals(__box(E numType::Mark)->ToString()))
theParity = EnumType::Mark;
else if (myItem->Equals(__box(E numType::None)->ToString()))
theParity = EnumType::None;
etc...

If anyone has any insight on converting a string or an integer to an
enumerated type, it would be greatly appreciated.

Thanks,
Jeremy

[Vladimir Nesterovsky]

Re: Strings ints and enums

> I'm having some problems working with enumerations. A function call to[color=blue]
> a 3rd party dll has in it's parameter list an enumerated type which
> connects me to a COM port. I'm trying to convert a stored parameter
> from a database into this enumerated value and can't seem to get
> anything to work. In some VB.NET code that was written, it works fine
> and that's the frustrating part. I've included some code below:
>
> Old vb.net code to get the enumerated value from a string:
>
> myEnum = [Enum].Parse(GetType( EnumType), "Enum Member")
>
> This code works fine, unfortunatly VB has no problems converting from
> an Object to EnumType. When I try the same thing in VC++ with:
>
> myEnum = Enum::Parse(__t ypeof(EnumType) , "Enum Member");[/color]

Did you try:

myEnum = *dynamic_cast<E numType *>(Enum::Parse( __typeof(EnumTy pe), "Enum
Member")); ?

--
Vladimir Nesterovsky
e-mail: vladimir@nester ovsky-bros.com
home: http://www.nesterovsky-bros.com

[Jeremy]

Re: Strings ints and enums

Thanks for the response Vladimir, but that doesn't seem to work either.

That throws the compiler error C2440, cannot convert from
'System::Enum' to 'EnumType', which doesn't make any sense to me
because I thought that was the point of *dynamic_cast.

[Vladimir Nesterovsky]

Re: Strings ints and enums

[color=blue]
> That throws the compiler error C2440, cannot convert from
> 'System::Enum' to 'EnumType', which doesn't make any sense to me
> because I thought that was the point of *dynamic_cast.[/color]

In fact I succeed in such a conversion:

__value enum Color
{
Red,
Green,
Blue
};

int main(int argc, char* argv[])
{
Color color = *dynamic_cast<C olor
*>(System::Enum ::Parse(__typeo f(Color), S"Green"));

System::Console ::WriteLine(col or);
}

--
Vladimir Nesterovsky
e-mail: vladimir@nester ovsky-bros.com
home: http://www.nesterovsky-bros.com

[Jeremy]

Re: Strings ints and enums

Okay, now I'm really confused. I've copied and pasted into a new
project, EXACTLY, and I get the compile error:

c:\Documents and Settings\jlueck \Desktop\C++.NE T Projects\Enum
Test\Enum Test.cpp(23): error C2440: 'initializing' : cannot convert
from 'System::Enum' to 'Color'

*shrug* Is there an include or using namespace that I should be
worring about? I'm running VS .NET 2003 on an XP box...

[Tomas Restrepo \(MVP\)]

Re: Strings ints and enums

Jeremy,[color=blue]
> Okay, now I'm really confused. I've copied and pasted into a new
> project, EXACTLY, and I get the compile error:
>
> c:\Documents and Settings\jlueck \Desktop\C++.NE T Projects\Enum
> Test\Enum Test.cpp(23): error C2440: 'initializing' : cannot convert
> from 'System::Enum' to 'Color'
>
> *shrug* Is there an include or using namespace that I should be
> worring about? I'm running VS .NET 2003 on an XP box...[/color]

Nope. It's just a long standing compiler problem. The solution is to use
static_cast<> instead with a bit of trickery. Try this:

Color color = *(static_cast<C olor
__box*>(System: :Enum::Parse(__ typeof(Color), S"Green")));


FWIW, I talked about this in more detail in an article I wrote a while back
on MSDN magazine (see the unboxing section):
http://msdn.microsoft.com/msdnmag/is...C/default.aspx


--
Tomas Restrepo
tomasr@mvps.org

http://www.winterdom.com/

[Jeremy]

Re: Strings ints and enums

Thanks Vladimir and Tomas for your help and that's an excellent article
Tomas.

Jeremy Lueck