Re: [boost] Q: defining a static data member for a template class

From: Ullrich Koethe (koethe_at_[hidden])
Date: 2000-11-01 13:13:57

Eric Weitzman wrote:
> 
> [Intro to Advanced C++ Template Techniques 101.]
> 
> Is there a a technique for defining a static data member for a template
> class other than using some macro kludge or requiring manual code inserted
> into an implementation file? For example
> 
>     in C.h:
> 
>       template <class T>
>       class C {
>           static int i_;
>       };
> 
>       #define DEFINE_STATIC_C(_t)   int C<_t>::i_ = 0;
> 
>     in C.cpp:
> 
>       typedef C<blah> MyC;
>       int MyC::i_ = 0;        // how can one avoid doing this?
>       int C<blah>::i_ = 0;    // ... or this?
>       DEFINE_STATIC_C(blah);  // ... or this?
> 

You may use a static member function containing a static variable, like
this:

      template <class T>
      class C {
          static int & i_() 
          { 
              static int i;
              return i;
          }
      };

C<Foo>::i_() can be used like a normal static data member, modulo
syntax.

Ulli
-- 
 ________________________________________________________________
|                                                                |
| Ullrich Koethe  Universität Hamburg / University of Hamburg    |
|                 FB Informatik / Dept. of Computer Science      |
|                 AB Kognitive Systeme / Cognitive Systems Group |
|                                                                |
| Phone: [phone]                Vogt-Koelln-Str. 30 |
| Fax:   [phone]                D - 22527 Hamburg   |
| Email: u.koethe_at_[hidden]               Germany             |
|        koethe_at_[hidden]                        |
| WWW:   http://kogs-www.informatik.uni-hamburg.de/~koethe/      |
|________________________________________________________________|