Issues with gcc and idl

Issues with gcc and idl

[Lorenzo Pesce]

Dear all,
I write statistical analysis software, in the form of functions  
(mostly), that people can call from a number of environments.
My functions are fortran subroutines (I opted for subroutines because  
C and "R" happily accepts them as they do not
put anything in the "return" of the function). These functions are  
built as a dynamically linked library (.so or .dll depending
upon the system).

I compile them using gcc-4.1.1 because later versions have problem  
creating dlls (but this is not why I am writing) as do
previous ones.

If I call a function that is parts of a module, the return appear to  
be a "null". However, when it is on its own, it seems to
return a number (which does not seem to have any meaning). R and C  
happily ignore that return, so I have no problems
in either case. However IDL seems to require one so I presume that  
other systems might have the same problem.

Do you know why a module subroutine contains no return value, while  
an independent subroutine does?
Do you know of any way to work around this inconsistency?

Thanks a lot,

Lorenzo