🚀 go-pugleaf

Niels Hilbrink <Niels@imacsg1.epfl.ch> wrote:
>Hi,
>
>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.
>
>Gr.
>Niels Hiblrink
>
>
>-- 
>
>   The most overlooked advantage to owning a computer is 
>   that if they foul up there's no law against wacking   
>   them around a little.                                 
>
>------------------------------------------------------------
>Koen D'Hondt			              Niels Hilbrink
>koen@@dutlhs1.lr.tudelft.nl      niels@dutlcc3.lr.tudelft.nl
>
>**** Ripley Software Development ****
>(finger niels@dutlcc3.lr.tudelft.nl for more information.)
>------------------------------------------------------------

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. 



typedef int     INTEGER;
typedef float   REAL;
typedef int     LOGICAL; 

#include "character.h"  // CHARACTER class (see below)

#define  SUBROUTINE        extern "C" void __stdcall
#define  INTEGER_FUNCTION  extern "C" INTEGER __stdcall
#define  REAL_FUNCTION     extern "C" REAL __stdcall



The CHARACTER class may look something like this:



#include <string.h>

/*
  class CHARACTER
  ===============
  A minimal class used when passing C-string arguments from C++ to
  FORTRAN 77 (received as FORTRAN 77 CHARACTER strings), and subsequently
  returned back to C++ as properly zero terminated c-strings.

  Method used for zero-termination:
  =================================
  When the CHARACTER destructor is activated (typically when the
  CHARACTER object goes out of scope within a C++ stub function)
  the zero-termination of the c-string is automatically managed.

  FORTRAN Assumptions:
  ====================
  (1) FORTRAN truncates assigned strings when CHARACTER variable is too short
  (2) FORTRAN pads CHARACTER variable with blanks when assigned string is short
  (3) FORTRAN represents a CHARACTER as a string pointer followed by a length

  Author: Carsten A. Arnholm, 20-AUG-1995
*/

class CHARACTER {
public:
    CHARACTER(char* cstring) : rep(cstring), len(strlen(cstring)) {};
    CHARACTER(char* cstring, const size_t lstr);
   ~CHARACTER();
public:
    char*   rep;  // Actual string
    size_t  len;  // String length, used by FORTRAN intrinsic function LEN()
};

inline CHARACTER::CHARACTER(char* cstring, const size_t lstr) : rep(cstring), len(lstr-1)
{
   size_t actual = strlen(rep);
   for(size_t i=actual;i<len;i++) rep[i]=' ';
   rep[len]='\0';
}

inline CHARACTER::~CHARACTER() {
   for(size_t i=strlen(rep)-1;i>=0;i--) {
     if(rep[i] != ' ') {
        rep[i+1] = '\0';
        break;
     }
   }
}


now you can declare FORTRAN subroutine prototypes in C++:

SUBROUTINE MYSUB(INTEGER& I1, CHARACTER C1, INTEGER& I2);

To create a portable solution, do the following:

a) Write header files for your FORTRAN libraries as shown above.
b) Compile FORTRAN code and create *.lib files.
c) Include the FORTRAN library header files in your C++ code.
d) Call FORTRAN according to above prototype example.
e) Compile C++ code and link with FORTRAN libraries
f) This executes directly for Visual C++ 2.1 & 4.0 in combination
   With Fortran Powerstation

porting to other machines:

a) Leave C++ and Fortran code untouched (single source requirement!)
b) Write a small C++ program that read your FORTRAN library header files, 
   and generate:
   b.1: a platform-specific header file for the fortran
        library. Here you deal with upper/lowercase names,
        trailing underscores, character lengths etc.
   b.2: a platform-specific *.CPP file containing inline
        functions that convert from 
        MYSUB(INTEGER& I1, CHARACTER C1, INTEGER& I2)
        to
        mysub_(int& I1, char* C1.rep, int& I2, int C1.len)

        (example above is for for SGI)
c) Compile & link this generated code with your application.
e) Should execute on basically any platform (UNIX, VMS, ...)


Other issues
============

a) Calling/linkage convention (C++).
   This is taken care of through the use of the statement: extern "C"
   This avoids name mangling which is not used in FORTRAN.

b) Routine names
   An ANSI standard FORTRAN routine name should be defined in UPPERCASE
   and max 6 characters. This does not, however, mean that the name
   used when calling from C/C++ should be in uppercase. On the SGI machine
   (i.e. unix) the routine must be in lowercase with a trailing underscore.
   On other unix boxes, you may need a leading underscore and/or uppercase
   name.

   Example:
   FORTRAN                              :          SUBROUTINE MYSUB
   Machine-dependent C++ prototype (SGI):     extern "C" void mysub_();

c) Parameter types and argument passing
   FORTRAN will always require parameters to be passed by reference
               
   FORTRAN                              :  SUBROUTINE MYSUB(IVAL)
                                           INTEGER          IVAL

   Machine-dependent C++ prototype (SGI):  extern "C" void mysub_(int& IVAL);


d) Machine dependent comparison of language types:

   FORTRAN               C++ 
   =======               ===
   INTEGER               int&
   REAL                  float&
   LOGICAL               int&
   CHARACTER             char*   (+ size_t length )
   DOUBLE PRECISION      double&

good luck,

Carsten Arnholm
ca@sesam.dnv.no 

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

-- 

   The most overlooked advantage to owning a computer is 
   that if they foul up there's no law against wacking   
   them around a little.                                 

------------------------------------------------------------
Koen D'Hondt			              Niels Hilbrink
koen@dutlhs1.lr.tudelft.nl      niels@dutlcc3.lr.tudelft.nl

**** Ripley Software Development ****
(finger niels@dutlcc3.lr.tudelft.nl for more information.)
------------------------------------------------------------

Niels Hilbrink 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.

> Niels Hiblrink

I was also scanning this newsgroup to find some info on linking Fortran 
with C++.(Using windows 3.1) I am using Borland C++ version 4.5 and 
Microsoft Fortran Powerstation. No luck so far. It might be possible 
doing this using DLL but the Microsoft Fortran makes no provision for 
compiling to dll, only .lib and .exe files. Can you please forward any 
info you might find.

Burt Wilson

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

In article <3110887E.41C6@imacsg1.epfl.ch>, Niels@imacsg1.epfl.ch says...
>
>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 ?
>

This is rather more difficult. To my knowlegde there are no standard 
methods for C++ call handling. So if your get this working by some trick
you may fail to make it work on any other machine. You could write a small C++
jacket which accepts opject A by reference and calls A.GetData() and call this
jacket from fortran: 
	 
      CALL GET_DATA_JACKET(OBJ, DATA)

However the C++ compiler mangles the names of routines. So your GET_DAT_JACKET
symbol would not be resolved unless you have a look at the map files for the 
true name (Something like GET_DATA_JACKETaB_12_876YFgDR... ) and use that name 
in fortran. Some compilers like GCC will let you define the true name by 
__asm__ directive. It is all very tricky and messy and not worth it at all.