Re: I can not compile code from <<modern c++ design>>

[Di Yang <diy at qualcomm dot com>]

At 12:00 4/8/2003 +0200, Matthias Oltmanns wrote:
> Am Die, 2003-04-08 um 10.48 schrieb Di Yang:
> >
> > Sorry, but I still failed at this point:
> >
>
> Hmmm ... me too :-) I've tested yesterday the wrong file.
>
> I've learned, that using sizeof with a function as parameter is a
> constant integer expression and therefore valid in using
> enumeration initializers.
>
> The question remaining is, why does the following not compile:
>
> #include <iostream>
>
> template<typename T>
> class Foo
> {
> public:
>   static T bar();
>
>   enum { test = sizeof(bar()) };
> };
>
> int main()
> {
>   std::cout << Foo<char>::test << std::endl;
> }
>
> > g++ -o conv conv.cc
> conv.cc: In instantiation of `Foo<char>':
> conv.cc:14:   instantiated from here
> conv.cc:14: invalid use of undefined type `class Foo<char>'
> conv.cc:5: declaration of `class Foo<char>'
> conv.cc:14: enumerator value for `test' not integer constant
>
> > g++ --version
> g++ (GCC) 3.2 20020903 (Red Hat Linux 8.0 3.2-7)
> Copyright (C) 2002 Free Software Foundation, Inc.
> This is free software; see the source for copying conditions.  There is
> NO
> warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
> PURPOSE.
>
> Is it a bug or does i still miss some point.

I don't know either, can someone familiar c++ standard explain this?

And with a FooHelper, it works:

// code start
#include <iostream>

template <typename T>
class FooHelper
{
public:
  static T bar();
};

template<typename T>
class Foo
{
public:
  enum { test = sizeof(FooHelper<T>::bar()) };
};


int main()
{
  std::cout << Foo<char>::test << std::endl;
}

// code end

Thanks.
Di

> cu
> Matthias