Re: How to pass String BYREF to C function?

Hi Marco,

 

Thanks for the response, but I still get an error ;-(

 

ctypes.ArgumentError: argument 2: <type 'exceptions.TypeError'>: wrong type

 

I tried this code:

 


import ctypes as c

import os

 

if __name__ == "__main__":

      if os.name=='nt':            

            userExit = c.cdll.LoadLibrary("libUserExits.dll")

            executeUserExit = userExit.executeUserExit

            executeUserExit.argtypes = [c.c_char_p, c.c_char_p]

            executeUserExit.restype = c.c_int

            stream = c.c_char_p()

            stream.value = "hello world"            

            exitResult = c.pointer(c.c_char_p())            

            result = executeUserExit(stream, exitResult)

      

      print "Finished"      

      

 

Do you have any other ideas?

 

Thanks for the help thus far ;-)

 

Lynton

 

From: marco cassisa [mailto:[email protected]] 
Sent: 17 August 2010 09:51 PM
To: Lynton Grice
Subject: Re: [ctypes-users] How to pass String BYREF to C function?

 

Hi 
I am absolutely no pro (just trying to use ctypes in these days), but AFICT
c_char_p is equivalent to char*, while pointer(c_char_p) is equivalent to
char**
So it seems to me that your C-declaration isn't equivalent to your
ctypes'one
Hope not to be wrong...
bye

marco

2010/8/17 Lynton Grice <[email protected]>

Hi there,

 

I have the following example C function that basically take 2 arguments and
"halves the first string" and puts that result in the second argument.

 


int executeUserExit(char *buffer, char **userExitResultBuffer){

   int total_len;

 

   total_len = strlen(buffer) / 2;

   *userExitResultBuffer = (char*) malloc(total_len);

   strncpy(*userExitResultBuffer, buffer, total_len);

   return 0;

}

 

I have call this from C code happily, but am having trouble from Python.

 

I created a DLL from the code above

 


import ctypes as c

import os

 

if __name__ == "__main__":

      if os.name=='nt':            

            userExit = c.cdll.LoadLibrary("libUserExits.dll")

            executeUserExit = userExit.executeUserExit

            executeUserExit.argtypes = [c.c_char_p, c.c_char_p]

            executeUserExit.restype = c.c_int

            stream = c.c_char_p()

            stream.value = "hello world"            

            exitResult = c.c_char_p()

            result = executeUserExit(c.pointer(stream), c.byref(exitResult))

            print result

      

      print "Finished"      

            

 

I am not too sure how the BYREF and POINTER stuff should work in the above
code?

 

I keep getting the error:

 

"ctypes.ArgumentError: argument 1: <type 'exceptions.TypeError'>: wrong
type"

 

I have been reading online but cannot find any nice example to follow, can
someone please give me some advise on this?

 

Your help is greatly appreciated ;-)

 

Lynton


----------------------------------------------------------------------------
--
This SF.net email is sponsored by

Make an app they can't live without
Enter the BlackBerry Developer Challenge
http://p.sf.net/sfu/RIM-dev2dev 
_______________________________________________
ctypes-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/ctypes-users

------------------------------------------------------------------------------
This SF.net email is sponsored by 

Make an app they can't live without
Enter the BlackBerry Developer Challenge
http://p.sf.net/sfu/RIM-dev2dev

_______________________________________________
ctypes-users mailing list
[email protected]
https://lists.sourceforge.net/lists/listinfo/ctypes-users