(j3.2006) (SC22WG5.5615) RE: F08/0139??

[Bill Long]

On Dec 20, 2015, at 7:24 PM, Malcolm Cohen <malcolm at nag-j.co.jp> wrote:

> Interp says
> 
>> Consider the program fragment:
>> 
>> Subroutine s() Bind(C,Name='Hello')
>>     Print *,'Hello'
>> End Subroutine
>> Subroutine s() Bind(C,Name='World')
>>   Print *,'World'
>> End Subroutine
>> 
>> This does not conform to Fortran 2003, and is not listed as an
>> extension in the Introduction to Fortran 2008, but the rules for
>> global names seem to indicate that this is now conforming.
> 
> 
> Bill Says:
>> You could alternatively make a module containing the text from the example, 
>> and have the main program use the module and call s().
> 
> Actually no.  The "rules for global names" in the question means that these 
> must be external subprograms, otherwise their names are Not global names. 
> I'll accept that this is not completely obvious if you stop reading at the 
> end of the program fragment!  (Though I cannot recall us *ever* giving an 
> example with internal or module procedures that did not either state that 
> they were such, or with enough boilerplate around them to make them such, so 
> I do think this reading is a trifle strained.)

Well, the ?strain? was because these might be actually called, and calling a subroutine like this requires an explicit interface.  Normally people to not write INTERFACE blocks, but rather put such routines in  a module.  This avoids mistakes from having the interface interface information in multiple places. In this case, it appears there is no way to avoid writing an explicit interface block if you want to call either routine, and you cannot have both interfaces visible in any scope where S is called. 

So, something like this example;

> cat test1.f90

 Subroutine s() Bind(C,Name='Hello')
     Print *,'Hello'
 End Subroutine
 Subroutine s() Bind(C,Name='World')
   Print *,'World'
 End Subroutine

 subroutine sub_hello ()
   interface
     Subroutine s() Bind(C,Name='Hello')
     End Subroutine
   end interface

   call s()  !  Causes Hello to be printed
 end subroutine sub_hello

 subroutine sub_world ()
   interface
     Subroutine s() Bind(C,Name='World')
     End Subroutine
   end interface

   call s()  !  Causes World to be printed
 end subroutine sub_world

program test
  call sub_hello()
  call sub_world()
end program test


> ftn test1.f90
> ./a.out
 Hello
 World
>



> 
>> A whole, compilable and executable example would much better.
> 
> Just inserting "containing the external subprograms" after "fragment" in the 
> first quoted line above would IMO be more than sufficient.

That seems sufficient to rule out the invalid programs of which such  fragment might have been a part. 

Cheers,
Bill


> 
> Cheers,
> -- 
> ..........................Malcolm.
> 
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Bill Long                                                                       longb at cray.com
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