ctypes with Compaq Visual Fortran 6.6B *.dll (Windows XP), passing of integer and real values

Tue Jan 27 16:41:31 EST 2009

Hello everybody
I am mainly a Fortran programmer and beginning to learn Python(2.5)
and OOP programming.
I hope in the end to put a GUI on my existing Fortran code.
Therefore I am also trying to learn Python's "ctypes" library.

Unfortunately the ctypes tutorial does not show simple examples so I
set up a simple fortran module
and Python script to test.
But even with passing Integer and Real values I get the right output
but with subsequent error:
ValueError: Procedure probably called with too many arguments (4 bytes
in excess)
The scripts exits then, so the second subroutine call does not happen.

>From reading comp.lang.python and comp.lang.fortran I understood that
passing character strings
may not be simple but I could not find any solution to my problem.
Maybe somebody can help me with solving it?

The Fortran module (footst.f90):

!
      module footst
!
      implicit none
!
!
!- End of module header
------------------------------------------------
!
!- Execution part of the module
----------------------------------------
!
!
      contains
!- Define procedures contained in this module.
!
!-----------------------------------------------------------------------
!
!
      subroutine foo1(int_tst)
      !DEC$ ATTRIBUTES DLLEXPORT :: foo1
      integer, intent(in):: int_tst
      write(unit=*, fmt="(a)") "Subroutine foo1(int_tst)"
      write(unit=*, fmt="(a, i4)") "a= ", int_tst
      end subroutine foo1
!
!
      subroutine foo2(real_tst)
      !DEC$ ATTRIBUTES DLLEXPORT :: foo2
      real, intent(in):: real_tst
      write(unit=*, fmt="(a)") "Subroutine foo2(real_tst)"
      write(unit=*, fmt="(a, f6.2)") "a= ", real_tst
      end subroutine foo2
!
!
      end module footst
!

The Python script (footst.py):

#!/usr/bin/env python
#
#
from ctypes import *
#
#
if __name__ == '__main__':
    tst=windll.LoadLibrary("f:\\scratch\\test2\\footst.dll")
#    tst.restype=None
#    tst.argtypes=(c_int)
    x=c_int(999)
    y=c_float(10.5)
    tst.footst_mp_foo1_(byref(x))
#    Passing Real values commented out, but leads to the same error
#    tst.footst_mp_foo2_(byref(y))
#
    main()
#
#

The DOS prompt output:

F:\Scratch\Test2>df /dll /iface=(cref,nomixed_str_len_arg)/
names:lowercase /assume:underscore footst.f90
Compaq Visual Fortran Optimizing Compiler Version 6.6 (Update B)
Copyright 2001 Compaq Computer Corp. All rights reserved.

/entry:_DllMainCRTStartup at 12
/ignore:505
/debugtype:cv
/debug:minimal
/pdb:none
F:\SysTemp\obj5B.tmp
dfordll.lib
msvcrt.lib
dfconsol.lib
dfport.lib
kernel32.lib
/out:footst.dll
/dll
   Creating library footst.lib and object footst.exp

Dump of file footst.dll

File Type: DLL

  Section contains the following exports for footst.dll

           0 characteristics
    497F5CC3 time date stamp Tue Jan 27 20:13:07 2009
        0.00 version
           1 ordinal base
           2 number of functions
           2 number of names

    ordinal hint RVA      name

          1    0 00001000 footst_mp_foo1_
          2    1 000010A6 footst_mp_foo2_

  Summary

        1000 .data
        1000 .rdata
        1000 .reloc
        1000 .text

F:\Scratch\Test2>footst.py
Subroutine foo1(int_tst)
a=  999
Traceback (most recent call last):
  File "F:\Scratch\Test2\footst.py", line 13, in <module>
    tst.footst_mp_foo1_(byref(x))
ValueError: Procedure probably called with too many arguments (4 bytes
in excess)

F:\Scratch\Test2>