How to interact with fortran code

[bachmeier via Digitalmars-d-learn]

On Thursday, 10 July 2014 at 12:12:20 UTC, Marc Schütz wrote:
> On Wednesday, 9 July 2014 at 15:09:08 UTC, Chris wrote:
>> On Wednesday, 9 July 2014 at 15:00:25 UTC, seany wrote:
>>> I apologize many times for this question, may be this had 
>>> already been answered somewhere, but considering today the 
>>> last of my nerve is broken, I can not really find the soution.
>>>
>>> So I have a D code, which acts as a central manager of all my 
>>> codes, reads user input, reads files, etc, and based on the 
>>> file readouts, I would like to pass some variables from the D 
>>> code to a fortran code, in binary format, perhaps, if such a 
>>> thing exists, instead of encoding to text/ ASCII first.
>>>
>>> I would also like to read some (not all) variables back from 
>>> the fortran code.
>>>
>>> The Fortran code resides in a subdirectory to the 
>>> path/to/d/code
>>>
>>> How to do this? is there a preffered way / easier than system 
>>> call way to interface D and Fortran code? This must be Fortan 
>>> code - these are the standard atmospheric chemistry codes.
>>>
>>> I apologize again if the question is stupid, trust me, today 
>>> all my nerves are broken.
>>
>> Off the top of my head I'd say you could try to interface 
>> Fortran and C. Then you could interface D and C, i.e. D > C > 
>> Fortran.
>>
>> http://fortranwiki.org/fortran/show/Generating+C+Interfaces
>> https://gcc.gnu.org/onlinedocs/gcc-3.4.4/g77/C-Interfacing-Tools.html
>
> To expand on that:
>
> You don't actually need to write a C glue layer between D and 
> Fortran. All you need to do is make your Fortran functions 
> accessible for C code. As I'm not familiar with Fortran, I 
> don't know how exactly that works, but it could involve telling 
> the compiler to use the right calling convention, and use the 
> right name mangling.

If you are able to use Fortran 2003 or later, Fortran's 
iso_c_binding makes it simple to expose Fortran functions to be 
called from C and vice versa. I don't know of any good online 
references, but a lot of good examples can be found in
the source for the Fortran interface to the GSL:

http://www.lrz.de/services/software/mathematik/gsl/fortran/index.html

An example of compiling and linking:

http://compgroups.net/comp.lang.fortran/usage-of-iso_c_binding/155309

If iso_c_binding is not available, then it's not as pretty:

http://www.yolinux.com/TUTORIALS/LinuxTutorialMixingFortranAndC.html