Extending Tcl with Fortran

There are three routes to linking Fortran code into Tcl. One is simply drive you Fortran application using expect. Secondly we might be able to import the Tcl C API into a format useful for Fortran and link Tcl into the Fortran module.

This section deals with wrapping the Fortran code into a Tcl package.

The GNU Compiler Collection is useful here as the Fortran component (g77) generates objects that are directly compatible with the C generated objects. Other Fortran compilers may also work. YMMV.

Two files are given below, power.f is Fortran77 code that provides a single function. tclpower.c is the C wrapper code that creates an interface callable from Tcl. To compile this using gcc/g77 on unix or the Mingw tools under Windows you should do:

  g77 -c power.f
  gcc -I/opt/tcl/include -DBUILD_power -DUSE_TCL_STUBS -c tclpower.c
  gcc -shared tclpower.o power.o /opt/tcl/lib/tclstub84.lib -o power01.dll

(fix the extensions for your system. Extending the TEA build system is simple enough, but I don't want to clutter the page here.)

Now you can use the library:

  % load power01.dll Power
  % power 5.5
  11803.0648209

AM I am working on a Fortran version for Critcl - the pieces are coming together! With this package, extending Tcl with Fortran will become much easier - see Critcl goes Fortran

AM (9 november 2007) What about extending a Fortran program, say, with a Fortran-like scripting language? See: Almost Fortran

power.f

 c     power.f - Copyright (C) 2003 Pat Thoyts <[email protected]>
 c
 c     Demonstrate linking Fortran subroutines into Tcl packages.
 c
 c     $Id: 8507,v 1.5 2007-03-10 07:00:14 jcw Exp $
 c
       double precision function power(x)
       double precision x

       power = x ** x

       end function power

tclpower.c

 /* tclpower.c - Copyright (C) 2003 Pat Thoyts <[email protected]>
  *
  * Demonstrate creation of a Tcl module that interfaces to Fortran 
  * subroutines.
  *
  * This package relies upon g77's ability to create objects that can be
  * easily linked into C generated modules.
  *
  * $Id: 8507,v 1.5 2007-03-10 07:00:14 jcw Exp $
  */

 #include <tcl.h>

 #ifdef BUILD_power
 #undef TCL_STORAGE_CLASS
 #define TCL_STORAGE_CLASS DLLEXPORT
 #endif

 #define PACKAGE "Power"
 #ifndef VERSION
 #define VERSION "0.1"
 #endif

 EXTERN int Power_Init(Tcl_Interp *interp);
 EXTERN int Power_SafeInit(Tcl_Interp *interp);

 /*
  * Declare the fortran functions - to be linked in to this executable. 
  */
 double power_(CONST double *d);

 /*
  * Tcl command procedures
  */
 static Power_ObjCmd(ClientData, Tcl_Interp *, int, Tcl_Obj *CONST []);

 /* ---------------------------------------------------------------------- */

 int
 Power_Init(Tcl_Interp* interp)
 {
 #ifdef USE_TCL_STUBS
     Tcl_InitStubs(interp, "8.1", 0);
 #endif

     // Call Tcl_CreateObjCommand etc.
     Tcl_CreateObjCommand(interp, "power", Power_ObjCmd, (ClientData *)NULL, 
                          (Tcl_CmdDeleteProc *)NULL);

     return Tcl_PkgProvide(interp, PACKAGE, VERSION);
 }

 int
 Test2_SafeInit(Tcl_Interp* interp)
 {
     // We don't need to be specially safe so...
     return Power_Init(interp);
 }

 /* ---------------------------------------------------------------------- */

 static int
 Power_ObjCmd(ClientData clientData, Tcl_Interp *interp,
               int objc, Tcl_Obj *CONST objv[])
 {
     double d, dr;
     int r = TCL_OK;

     if (objc != 2) {
         Tcl_WrongNumArgs(interp, 1, objv, "real value");
         r = TCL_ERROR;
     }

     if (r == TCL_OK)
         r = Tcl_GetDoubleFromObj(interp, objv[1], &d);

     if (r == TCL_OK)
     {
         dr = power_(&d);
         Tcl_SetObjResult(interp, Tcl_NewDoubleObj(dr));
     }

     return r;
 }

 /* ---------------------------------------------------------------------- */
 /* 
  * Local variables:
  *   mode: c
  *   indent-tabs-mode: nil
  * End:
  */