Initializing static const class members

[Daniel Switkin]

Hi there,

I'm trying to do the following:

class tLimits {
static const int kIntMin = 0; // fine
static const float kFloatMin = 0.0f; // breaks
};

and I get this message:

error C2864: 'kFloatMin' : only const static integral
data members can be initialized inside a class or struct

We've been using this technique fine under gcc, both 2.9
and 3.3. Is there any reason VC++ .NET 2003 can't handle
a floating point static const initialized within the
header? Pushing the definition into the .cpp file will
cost a memory access which I don't want. Since I'm
passing classes like this to templates there's a big
rippling effect in this limitation. I'd really like to
see this fixed in a future release.

Thanks,
Daniel Switkin

[Tomas Restrepo \(MVP\)]

Hi Daniel,

I'm trying to do the following:

class tLimits {
static const int kIntMin = 0; // fine
static const float kFloatMin = 0.0f; // breaks
};

and I get this message:

error C2864: 'kFloatMin' : only const static integral
data members can be initialized inside a class or struct

We've been using this technique fine under gcc, both 2.9
and 3.3. Is there any reason VC++ .NET 2003 can't handle
a floating point static const initialized within the
header? Pushing the definition into the .cpp file will
cost a memory access which I don't want. Since I'm
passing classes like this to templates there's a big
rippling effect in this limitation. I'd really like to
see this fixed in a future release.

As Jeff pointed out, technically speaking, VC++ is perfectly conformant in
this regard, since the ISO spec defines constant initializers only for
static members of const integral or const enumeration types (see 9.4.2 sub 4
for the details).

--
Tomas Restrepo
to****@mvps.org

[Daniel Switkin]

>As Jeff pointed out, technically speaking, VC++ is
perfectly conformant in

this regard, since the ISO spec defines constant initializers only forstatic members of const integral or const enumeration types (see 9.4.2 sub 4for the details).

Thanks for the response, both of you. I suppose this is
one of those nice extensions I've gotten used to.

There are real optimizations to be had here, though. For
example, if I have a float constant of 1.0f in the
header, this lets gcc move 0x3f800000 directly rather
than doing a memory access, which could miss the cache.
I'm currently using these float constants for default
arguments to inline functions (i.e. the alpha channel of
a color class), among other uses.

So it may not be strictly required by the language, but
it would be nice to have (especially when using
templates - this is causing some integer code to slow
down as a result).

Cheers,
Daniel Switkin