Re: How to add code to a C wrapper function generated by SWIG (for Python)

From what I can see, implementing the destructor in an %extend results in a
delete_<Class> function and a _wrap_delete<Class> function being generated
in the Swig wrapper code.

However, having taken a closer look, I see I did not remember all of this
correctly. I was not %ignore'ing the destructor; the destructor was
already private in the class being wrapped. Instead there was a public
destroy method and it is _this_ that is being %ignore'd in the wrapper.
Then the C++ destroy function is used to implement the destructor defined
in the %extend section.

So I do not know if this is at all useful for the question being asked here.

On Fri, 22 Jan 2021 at 11:05, Rokas Kupstys via Swig-user <
[email protected]> wrote:

> And you have to call destructor manually instead of wrapper handling it?
>
> -- Rokas Kupstys
>
> On 2021-01-22 12:57, Ian Boyd wrote:
>
> Yes, that's the point - to prevent the generation of the wrapper. The
> destructor is then implemented using %extend.
>
> The reason I remember this approach is that I had to fix up some code a
> couple of years ago that had done something like this. I ran into issues
> because of a Swig upgrade. There is a small thread in the archives:
> https://sourceforge.net/p/swig/mailman/message/36465099/
>
> It was someone else's code I was fixing up. I am not an expert on this,
> and it might not be the right approach, but I thought I would mention in
> case it might be useful in this case.
>
> On Fri, 22 Jan 2021 at 10:38, Rokas Kupstys via Swig-user <
> [email protected]> wrote:
>
>> How would that work? %ignore would prevent generation of wrappers for
>> ignored thing. I dont see how ignored destructor would then be called by
>> wrapper code at appropriate time.
>>
>> -- Rokas Kupstys
>>
>> On 2021-01-22 12:12, Ian Boyd wrote:
>>
>> Another option I think I have seen before is to use %ignore to prevent
>> Swig from generating a destructor and then use %extend to implement a
>> custom one.
>>
>> On Fri, 22 Jan 2021 at 10:00, Rokas Kupstys via Swig-user <
>> [email protected]> wrote:
>>
>>> Maybe %newobject + %newfree typemaps would work for you in this case?
>>>
>>> -- Rokas Kupstys
>>>
>>> On 2021-01-22 10:48, lille stor wrote:
>>>
>>> Hi,
>>>
>>> When generating a Python wrapper using SWIG, many C wrapper functions
>>> are generated. One of them is called "_wrap_delete_Cursor" which looks
>>> like this (I have stripped it to the bare minimum):
>>>
>>>    SWIGINTERN PyObject *_wrap_delete_Cursor(PyObject *self, PyObject *args) {
>>>
>>>        // some generated C code by SWIG
>>>
>>>        // need to add code to call a C function to release allocated memory
>>>
>>>    }
>>>
>>> This function is called when the object Cursor (created in Python) no
>>> longer exists. Now, my problem is that I have some allocated memory on the
>>> C side that needs to be released before existing the function (otherwise,
>>> there will be memory leaks).
>>>
>>> Do you know how I can add a line of code this function to release
>>> memory? All help is really welcome!
>>>
>>> L.
>>>
>>>
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