Stefan Behnel schrieb:
> Hi,
>
> welcome to Cython.
>
> Martin Gysel wrote:
>> I'm quite new to cython and try to bind some c code to python. Now I'm
>> not sure if I understood the cython doc correctly since what I'm trying
>> do do doesn't work :-(
>> It looks like this:
>>
>> cdef class Cobj:
>> cdef a_c_struct_t *loop
>>
>> def __init__(self):
>> self.loop = c_lib_call()
>> c_lib_call_reg_callback(<c_cb_t>self.callback, NULL)
>>
>> cdef void callback(self, void *userdata) with gil:
>> # but here, self.loop seems to be NULL instead of something
>> # to test this:
>> # if self.loop == NULL: print "isNull"
>> doSomething(self.loop)
>>
>> in the callback self.loop is NULL but in the init it wasn't. is it
>> possible to access self and its members in a c callback?
>
> Yes. However, since "callback" is a C function (and not a Python method),
> it cannot remember what instance it belongs to. You will have to pass along
> the pointer to its Python object yourself. This is what the "userdata"
> pointer is there for. It should work to do this:
>
>
> cdef class Cobj:
> cdef a_c_struct_t *loop
>
> def __init__(self):
> self.loop = c_lib_call()
> c_lib_call_reg_callback(<c_cb_t>self.callback, <void*>self)
>
> cdef void callback(self) with gil:
> if self.loop == NULL: print "isNull"
> doSomething(self.loop)
thanks Stefan, but now it is a little bit more complex as my callback
expects more than one argument
to register:
c_lib_call_reg_callback(mycontext, <c_cb_t>self.callback, <void*>self)
and the callback (as plain c fuction)
void callback(context *c, void *userdata)
according to your code above, the first argument where the callback gets
called is the first argument of the declared callback (in code above,
cb(userdata) -> callback(self): userdata->self)
so I assume if I have more arguments it works in the same way but then
self would be context instead of userdata (at this point code seems to
get kind of ugly):
cdef void callback(self, void *userdata)
now I'm asking myself what's the benefit to declare a c callback in the
class rather then outside and and call another class method from there,
like this:
cdef void callback(context *c, void *userdata):
doWhatHasToBeDone(c)
anotherOperation(<a_c_struct_t *>(<Cobj>userdata).loop)
itsDone((<Cobj>userdata).cbDone())
what's the best way to do such things?
/martin
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