[Numpy-discussion] Calling routines from a Fortran library using python

[Nils Wagner]

On Thu, 11 Mar 2010 13:01:33 +0100
  Dag Sverre Seljebotn <dagss at student.matnat.uio.no> 
wrote:
> Nils Wagner wrote:
>> On Mon, 22 Feb 2010 22:18:23 +0900
>>   David Cournapeau <cournape at gmail.com> wrote:
>>   
>>> On Mon, Feb 22, 2010 at 10:01 PM, Nils Wagner
>>> <nwagner at iam.uni-stuttgart.de> wrote:
>>>
>>>     
>>>> ar x test.a
>>>> gfortran -shared *.o -o libtest.so -lg2c
>>>>
>>>> to build a shared library. The additional option -lg2c 
>>>> was
>>>> necessary due to an undefined symbol: s_cmp
>>>>       
>>> You should avoid the -lg2c option at any cost if 
>>> compiling with
>>> gfortran. I am afraid that you got a library compiled 
>>> with g77. If
>>> that's the case, you should use g77 and not gfortran. 
>>> You cannot mix
>>> libraries built with one with libraries with another.
>>>
>>>     
>>>> Now I am able to load the shared library
>>>>
>>>> from ctypes import *
>>>> my_lib = CDLL('test.so')
>>>>
>>>> What are the next steps to use the library functions
>>>> within python ?
>>>>       
>>> You use it as you would use a C library:
>>>
>>> http://python.net/crew/theller/ctypes/tutorial.html
>>>
>>> But the fortran ABI, at least for code built with g77 
>>> and gfortran,
>>> pass everything by reference. To make sure to pass the 
>>> right
>>> arguments, I strongly suggest to double check with the 
>>> .h you
>>> received.
>>>
>>> cheers,
>>>
>>> David
>>> _______________________________________________
>>> NumPy-Discussion mailing list
>>> NumPy-Discussion at scipy.org
>>> http://mail.scipy.org/mailman/listinfo/numpy-discussion
>>>     
>>
>> Hi all,
>>
>> I tried to run the following script.
>> The result is a segmentation fault.
>> Did I use byref correctly ?
>>
>> from ctypes import *
>> my_dsio = CDLL('libdsio20_gnu4.so')      # loading 
>>dynamic 
>> link libraries
>> #
>> # FORTRAN : CALL DSIO(JUNCAT,FDSCAT,IERR)
>> # 
>> #     int 
>>         I,J,K,N,IDE,IA,IE,IERR,JUNIT,JUNCAT,NDATA,NREC,LREADY,ONE=1;
>> #     Word        BUF[100],HEAD[30];
>> #     char        *PATH,*STRING;
>> #     char        *PGNAME,*DATE,*TIME,*TEXT;
>> #     int         LHEAD=30;
>> #
>> # C       : DSIO(&JUNCAT,FDSCAT,&IERR,strlen(FDSCAT));
>> #
>>
>>
>> IERR    = c_int()
>> FDSCAT  = c_char_p('dscat.ds')
>> JUNCAT  = c_int()
>> LDSNCAT = c_int(len(FDSCAT.value))
>> print
>> print 'LDSNCAT', LDSNCAT.value
>> print 'FDSCAT' , FDSCAT.value  , len(FDSCAT.value)
>>
>> my_dsio.dsio(byref(JUNCAT),byref(FDSCAT),byref(IERR),byref(LDSNCAT)) 
>> # segmentation fault
>> print IERR.value
>>
>>
>> Any idea ?
>>   
> You shouldn't have byref on FDSCAT nor LDSNCAT, as 
>explained by this line:
> 
> # C       : DSIO(&JUNCAT,FDSCAT,&IERR,strlen(FDSCAT));
> 
> Dag Sverre
  

Sorry, I am newbie to C. What is the correct way ?

Nils