ctypes: delay conversion from c_char_p to string

Brendan Miller catphive at catphive.net
Thu Apr 22 00:29:24 CEST 2010

Here's the method I was using. Note that tmp_char_ptr is of type
c_void_p. This should avoid the memory leak, assuming I am
interpreting the semantics of the cast correctly. Is there a cleaner
way to do this with ctypes?

    def get_prop_string(self, prop_name):
        # Have to work with c_void_p to prevent ctypes from copying to a string
        # without giving me an opportunity to destroy the original string.
        tmp_char_ptr = _get_prop_string(self._props, prop_name)
        prop_val = cast(tmp_char_ptr, c_char_p).value
        return prop_val

On Wed, Apr 21, 2010 at 3:15 PM, Brendan Miller <catphive at catphive.net> wrote:
> I have a function exposed through ctypes that returns a c_char_p.
> Since I need to deallocate that c_char_p, it's inconvenient that
> ctypes copies the c_char_p into a string instead of giving me the raw
> pointer. I believe this will cause a memory leak, unless ctypes is
> smart enough to free the string itself after the copy... which I
> doubt.
> Is there some way to tell ctypes to return an actual c_char_p, or is
> my best bet to return a c_void_p and cast to c_char_p when I'm reading
> to convert to a string?
> Thanks
> Brendan

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