Re: [ctypes-users] Procedure called with not enough arguments (4bytesmissing) or wrong calling convention

[Victor B. <cty...@vi...>]

On Sun, Dec 13, 2009 at 11:55 PM, Victor Blomqvist <cty...@vi...>
wrote:
>
> On Sun, Dec 13, 2009 at 10:11 PM, Mark Tolonen <met...@gm...<metolone%2B...@gm...>>
wrote:
>>
>> > Thanks for your help, problem not solved but at least a little bit
>> > forward:
>> > When I try your code it does work fine compiled with cl, but get the
same
>> > error when compiled with gcc. And thanks to the printf I can see that
the
>> > error is created at the return statement:
>> >> python cp.py
>> > bb=(1.000000,2.000000,3.
>> > 000000,4.000000)
>> > v=(10.000000,12.000000)
>> > Traceback (most recent call last):
>> >  File "cp.py", line 31, in <module>
>> >    r = cpBBWrapVect(bb,Vec2d(10,12))
>> > ValueError: Procedure called with not enough arguments (4 bytes
missing)
>> > or
>> > wrong calling convention
>> >
>> > Apparently its something with return of Vec2d's (probably structs in
>> > general), but I don't know what or how to fix it?
>> >
>> > The full c library uses c99 and is mainly developed on linux/mac,
meaning
>> > it
>> > is a bit tricky to compile with visual studio/cl so the best and
easiest
>> > would be if it could be made to work with mingw / gcc to minimize the
work
>> > required to compile it. But I guess I will have to reconsider if I
don't
>> > get
>> > it to work properly..
>>
>> A possibility:  passing and returning structures on the stack  vs. with
>> pointers is likely compiler dependent.  If you have the option to
re-write
>> the function to avoid this that may fix the issue.
>>
>> -Mark
>
Yes, I changed the function to return a pointer instead and then it worked
as expected (same thing with ints or other simple types). However, I don't
think there's any chance to convince the author to change all returned
structs to struct pointers instead, and while I can modify it myself it
would be hard to maintain.
>
> But at least it feels like the problem is found, something with how gcc
return structs vs how ctypes expect them. I thought that a dll was callable
from different programs regardless of the compiler used. I wonder if there's
a compiler option to change the behaviour to something ctypes can
understand, or if its possible to set something in the wrapper python code..
>
> /Victor
>

Forgot to reply to the list :)
Sorry for the extra mail Mark.

/Victor