c interop update..

["Christopher D. Rickett" <crickett at lanl dot gov>]

after seeing some of the mail come across mentioning the c interop of f03, 
i thought i'd give an update.

in addition to the email i sent a while back, i now have the compiler 
allowing for the "use, intrinsic :: iso_c_binding" and generating the 
appropriate symbols for the named constants that are used as the kind 
parameters.  i haven't completed the list of the named constants; this is 
a fairly trivial thing but is dependent on what the C compiler supports, 
so i have stuck to the basic c int, long, float, double, long double, and 
the c_ptr and c_funptr derived types.  these seem to be working, and the 
compiler is correctly enforcing that a bind(c) routine has c 
interoperable params.  

also, the VALUE attribute appears to be working, at least for the 
interoperable kinds that i have implemented.  that is, the primitive types 
and derived types can be passed between c and fortran either way, or from 
fortran to fortran.  i've recently been testing this, especially for 
derived types, and the results so far are correct.  even if fortran is 
only given a reference to an object from C, it can still "promote" it to a 
by-value parameter if the given fortran procedure calls another procedure 
(C or fortran) that expects it by value.  

i've added a fair amount of error checking, though there's much more to do 
of course.  for example, i've added error checking to the declarations of 
common blocks and derived types that are bind(c) to make sure fields 
within them are interoperable.  at this point, the common blocks and 
derived types seem to be working.  assumed size arrays that i've tested 
are working, either as a param or as a global variable.  i've recently 
been adding symbol attribute checks in check_conflict() to make sure 
things like value and allocatable do not go together, etc.  there's more 
to add here, but that's fairly straight-forward.  one thing i'm not 
testing (or preventing i should say) is for the params to a bind(c) 
procedure to be allocatable, optional, assumed-shape,  or fortran 
pointers.  it is my understanding that this is to be allowed in fortran 2008.  

i'm currently working on the procedures that are in the iso_c_binding 
module.  i'm focusing on the c_ptr ones first, then will move onto the 
procpointer ones after i've added the procedure pointer type.  these 
procedures are being built into libgfortran.  

the biggest obstacle left, i'd guess, is the addition of the procedure 
pointer to fortran.  otherwise, what seems to be left is fairly 
straight-forward.  i plan on starting the paperwork soon so hopefully i 
can submit the changes.  also, a colleague of mine, Craig Rasmussen, will 
be doing the paperwork also so he can submit some additions also (he'll 
have to explain more himself).  Craig has been a large help in 
implementing the f03 c interop features.

Thanks.
Chris