Hi Gerry,
I think I see whats going on. If the pointer that is being passed to
> pointer_to_array is void, then you get a array of void pointers. In my case
> the original array was an array of strings, so...
>
> arr = pointer_to_array(cbdata, 4, true)
> println(bytestring(convert(Ptr{Uint8}, val[1])))
>
Was the original array of strings allocated by Julia, or in your C function?
I think your solution is close. It would be slightly cleaner if you
declared you function to take a Ptr{Ptr{Uint8}}:
function my_callback(cbdata::Ptr{Ptr{Uint8}})
arr = pointer_to_array(cbdata, 4) # arr of length 4
println(bytestring(arr[1]))
nothing
end
cbfunc = cfunction(my_callback, Void, (Ptr{Ptr{Uint8}},))
Does this work?
BTW, have you seen Steven Johnson's blog post on Passing Julia Callback
Functions to C <http://julialang.org/blog/2013/05/callback/>? I've found
it quite useful.
Cheers!
Kevin
> Is there a better way to do this?
>
> Thanks,
> -G
>
>
> On Sunday, August 10, 2014 4:23:29 AM UTC-5, Gerry Weaver wrote:
>>
>> Hi Kevin,
>>
>> I found the pointer_to_array function, but I'm having some trouble
>> figuring how to call it correctly. I assume it has something to do with the
>> pointer being a void pointer. I've been searching for something that might
>> give me a clue how to do this, but I haven't found anything very useful so
>> far.
>>
>> Thanks,
>> -G
>>
>> On Sunday, August 10, 2014 4:06:52 AM UTC-5, Kevin Squire wrote:
>>>
>>> Hi Gerry,
>>>
>>> "pointer_to_array" is probably what you're looking for. See
>>> http://julia.readthedocs.org/en/latest/manual/calling-
>>> c-and-fortran-code/#accessing-data-through-a-pointer for more
>>> information.
>>>
>>> Cheers,
>>> Kevin
>>>
>>>
>>> On Sun, Aug 10, 2014 at 1:17 AM, Gerry Weaver <[email protected]> wrote:
>>>
>>>> I forgot to mention that I'm trying to accomplish this with arrays
>>>> right now. I can pass a Julia array to C and access it there, but I can't
>>>> figure out how to convert it back to a Julia array from a C void pointer
>>>> when calling back to Julia from C.
>>>>
>>>>
>>>> On Sunday, August 10, 2014 1:57:18 AM UTC-5, Gerry Weaver wrote:
>>>>>
>>>>> Hello All,
>>>>>
>>>>> I have a C function called mycfunc that takes a callback function
>>>>> pointer (cbfunc) and a void pointer (cbdata) as arguments. mycfunc calls
>>>>> the callback function (cbfunc) passing the void pointer (cbdata) as its
>>>>> argument. I'm trying to figure out how to pass a Julia type as the void
>>>>> pointer argument and convert it back to the Julia type in the Julia
>>>>> function passed as the callback function argument. I can do this with a
>>>>> simple string, but I'm having some difficulty in figuring out how to do it
>>>>> with arrays and other types. Any advice on this would be much appreciated.
>>>>>
>>>>>
>>>>> typedef int (* mycallback)(void *cbdata);
>>>>>
>>>>> void mycfunc(mycallback cbfunc, void *cbdata)
>>>>> {
>>>>> cbfunc(cbdata);
>>>>> }
>>>>>
>>>>> Thanks,
>>>>> -G
>>>>>
>>>>>
>>>>>
>>>
