using fortran common block from dll created by gfortran

[LMH]

If you having trouble communicating with the dll, it might make more
sense to create a generic c dll and embed the fortran in the c dll as a
subroutine. It is generally not a problem to call a fortran subroutine
from c code though there are some syntax specifics to follow. Your
communication with the dll could follow standard c protocols. Since c
code and fortran code will have their own namespaces, your fortran
includes, common block, etc, shouldn't be a problem since those
variables will only be linked to the fortran objects. Your fortran src
files will be run through the fortran pre-processor so your common block
should be fine. Your c src files will be run through the c
pre-processor. The c objects won't know anything about the fortran
global variables but you can exchange what you need to between the c and
fortran in the call to the fortran subroutine. You end up with two
copies of allot of things but this is a decent way to get fotrran code
to talk to the modern programming world.

The only way I know to use the same memory namespace for both c and
fortran files is to run the fortran through the c pre-processor (name
your fortran src files .FPP). This lets you use c style includes and
compiler directives in your fortran code but does not support a common
block. You would have to declare global variables in c style includes.

LMH


Satish Balay wrote:
> Thanks for the note.
> 
> I had previously tried something similar - using the directives from
> http://gcc.gnu.org/onlinedocs/gfortran/GNU-Fortran-Compiler-Directives.html
> 
> However - I get errros.
> 
>>>>>>>>>>>
> balay@ps4 ~/junk
> $ cat cb_func.f
>       subroutine cb_func()
> !GCC$ ATTRIBUTES DLLEXPORT :: cb_func, /cb/
>       common /cb/ cvar
>       integer cvar
>       cvar = 2
>       end
> 
> balay@ps4 ~/junk
> $ gfortran -c cb_func.f 
> cb_func.f:2.40:
> 
> *GCC$ ATTRIBUTES DLLEXPORT :: cb_func, /cb/                             
>                                         1
> Error: Invalid character in name at (1)
> 
> balay@ps4 ~/junk
> $ 
> <<<<<<<<<<<<<
> 
> Wrt 'common blocks' vs 'module' - this usage is part of a c library
> supporting fortran interfaces [and works generally on various OSes,
> compilers]. We haven't worked with dlls on windows much. However this
> issue came up on such an attempt with cgwin/gnu compilers.
> 
> PS: I'm not subscribed to the ML - it would be great if I'm included in cc:
> 
> Thanks,
> Satish
> 
>>>>>>>>
> Hi,
> 
> while this is not directly related to gfortran on Cygwin, this article
> might help you appreciate the issues involved:
> https://software.intel.com/en-us/node/535307
> 
> Are you bound to common blocks? If not, you may get better results
> when you put the data in a module.
> 
> Regards,
> 
> Arjen
> 
> On Tue, 23 Jun 2015, Satish Balay wrote:
> 
>> Hi Cygwin,
>>
>> I'm debuging an issue with dlls with cygwin gnu compilers - and have
>> narrowed down the issue to the attached test case [script].
>>
>> Could you guide me to correct usage of 'fortran common block' with dlls?
>>
>> [In this example - using fortran 'common block' via static library
>> works. However the same code using a .dll fails]
>>
>> Thanks,
>> Satish
>>
>> ---------
>>
>> balay@ps4 ~/junk
>> $ ./cb_test.sh 
>> + cat
>> + cat
>> + rm -f '*.o' '*.dll' '*.a' '*.exe'
>> + gfortran -c cb_func.f cb_main.f
>> + ar cr libcb_static.a cb_func.o
>> + gfortran cb_main.o -L. -lcb_static -o cb_main_static
>> + gfortran -shared -o libcb_dynamic.dll cb_func.o
>> + gfortran cb_main.o -L. -lcb_dynamic -o cb_main_dynamic
>> + ./cb_main_static
>>  GOOD COMMON BLOCK
>> + ./cb_main_dynamic
>>  BAD COMMON BLOCK
>>
>>
>> balay@ps4 ~/junk
>> $ uname -a
>> CYGWIN_NT-6.1 ps4 2.0.4(0.287/5/3) 2015-06-09 12:22 x86_64 Cygwin
>>
>> balay@ps4 ~/junk
>> $ gfortran --version
>> GNU Fortran (GCC) 4.9.2
> 
> 
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