Tobias:

It's not possible in Fortran 90 or Fortran 95, but in Fortran 2003 or
Fortran 2008 you can define an abstract interface thus:

  abstract interface
    subroutine F ( Arg )
      real :: Arg
    end subroutine F
  end interface

You can then access that interface either within the same scope as its
definition, or by use or host association, and declare a procedure
pointer, procedure dummy argument, or type-bound procedure by reference
to it:

  subroutine Some_Sub ( A, My_F )
    real :: A
    procedure(F) :: My_F
    ....
  end subroutine Some_Sub

See subclauses 4.5.3, 4.5.4, 12.3.2.1 and 12.3.2.3 of
http://j3-fortran.org/doc/year/04/04-007.pdf.


On Thu, 2010-08-05 at 15:09 -0700, Tobias Brandt wrote:
> Hi all,
> I'm just starting out with Fortran 90 coming from C++ and need some
> help. In C++ you can define a function pointer type like so:
> 
> 
> typedef void (*mytype) (float);
> 
> 
> and then use it as a type for function parameters:
> 
> 
> void some_function (float a, mytype f)
> {
>     f(a);
> }
> 
> 
> void some_other_function (float a, mytype f)
> {
>     f(2*a);
> }
> 
> 
> 
> 
> Now, if I want to do the same in Fortran 90, I have to define the same
> inteface twice:
> 
> 
> subroutine some_sub (a, f)
>     real :: a
>     interface
>         subroutine f (arg)
>             real :: arg
>         end subroutine
>     end interface
>     call f(a)
> end subroutine
> 
> 
> subroutine some_sub (a, f)
>     real :: a
>     interface
>         subroutine f (arg)
>             real :: arg
>         end subroutine
>     end interface
>     call f(2*a)
> end subroutine
> 
> 
> 
> 
> Is it possible to somehow "reuse" the interface definition by
> declaring it outside the subroutines or in a different module?
> 
> 
> Regards,
> Tobias