🚀 go-pugleaf

Niels Hilbrink <Niels@imacsg1.epfl.ch> wrote:
>Carsten Arnholm wrote:
>> 
>> Niels Hilbrink <Niels@imacsg1.epfl.ch> wrote:
>
>> >I have to link a piece of fortran code with c++ code but since if never
>> >done that before I'd like to know a) can it be done and b) is it
>> >difficult.
>> >
>> >Everything concerning this subject is welcome.
>> 
>> Hi there,
>> 
>> Mixed language programming (C++/FORTRAN 77) is not as hard as
>> it may seem.
>> 
>> The only non-trivial problem you must solve is fortran CHARACTERs.
>> You need to write a minimal CHARACTER class in C++.
>> 
>> If you require single-source portability, it becomes slightly
>> more complicated, but not impossible.
>> 
>> Below follows a summary of some stuff that I have done, plus
>> some additional thoughts.
>
>As understand it, this is the way to go if you want to call fortran routines 
>in a c++ code. But what if you  want to do go the other way around ? 
>
>So how do I call an data member from a c++ class in fortran ?
>say I want to call a member function called GetData() in fortran so
>how do I transplate Class->GetData() in fortran ?
>
>Thanxs,
>Niels


Well, I have never done that, but generally I guess you would have to

a) Write a C-API (i.e. a set of C++ functions with C linkage) for the 
   things you want to call from FORTRAN. Do this by declaring the API 
   functions as extern "C" (avoids name mangling).

b) Provide some kind of pointer in the API to identify objects. These 
   pointers are not used by FORTRAN, they're just object identifiers.


Here's my suggestion (I don't know if it works).


C++:

   class myClass {
   public:
       myMemFunc();
   }


C-API:

   extern "C" int myClass_create() 
   {
       myClass* myObject = new myClass;
       return (int) (*myObject);
   }

   extern "C" void myClass_myMemFunc(int& object)  
   {
       myClass* myObject = (myClass*) &object;
       myObject->myMemFunc();
   }


FORTRAN:

    PROGRAM TEST
    INTEGER MYOBJ
    MYOBJ = myClass_create();
    myClass_myMemFunc(MYOBJ)
    END


Anyone done this, or similar ?

Carsten
ca@sesam.dnv.no