A Question about ctypes and a function f(void **)

[sapsi]

Hello,
I have a C function f(void**,int *), in which it writes some
information (it is a RGB32 image).

Here is what i do
rowlength=c_int ()
data=c_void_p()
d=pointer(data)
f(d,byref(rowle ngth)
The call works (no segmentation fault), now how do i access the data
in d? Because i need to pass it to a another function QImage that
takes void* as its first parameter.

If i do d.contents i get c_void_p(306747 8024L)

All suggestions welcome.
Regards
Saptarshi

[Nick Craig-Wood]

Re: A Question about ctypes and a function f(void **)

sapsi <saptarshi.guha @gmail.comwrote :

I have a C function f(void**,int *), in which it writes some
information (it is a RGB32 image).
>
Here is what i do
rowlength=c_int ()
data=c_void_p()
d=pointer(data)
f(d,byref(rowle ngth)
The call works (no segmentation fault), now how do i access the data
in d? Because i need to pass it to a another function QImage that
takes void* as its first parameter.
>
If i do d.contents i get c_void_p(306747 8024L)

You almost answered your own question!

d.contents is a c_void_p ie a (void *) so you can pass d.contents to
QImage directly I would have thought.

If you want to actually read the data from python then you'll need to
cast it to some other pointer type than c_void_p first, eg

>>d

c_void_p(136692 916)

>>s = c_char_p(d.valu e)
>>s

c_char_p(136692 916)

>>s.value

'hello'

>>>

or use ctypes.memmove to copy the data out to somewhere else.

--
Nick Craig-Wood <nick@craig-wood.com-- http://www.craig-wood.com/nick