[C++-sig] Pointers to simple types, arrays and arrays of pointers to types

[Nicodemus]

Niall Douglas wrote:

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>My apologies if this is really simple. I did search ASPN and didn't 
>get anything relevent after 20 mins, so ...
>
>I have everything compiling except for eight of over 100 source files 
>(thanks again to everyone here!). Most of these won't compile because 
>some method returns a pointer to a simple type eg;
>
>typedef unsigned long FXColor;
>
>class FXImage
>{
>public:
>    FXColor* getData() const;
>};
>
>using namespace boost::python;
>
>void Export_FXImage()
>{
>    class_< FXImage >("FXImage")
>		.def("getData", &FXImage::getData, return_internal_reference< 1 
>  
>
>>())
>>    
>>
>    ;
>};
>
>This won't compile because FXColor is not a class. Ideally I'd like 
>the python side to be able to access the array of FXColor's being 
>returned - no limits are needed because other methods return the 
>length.
>

I don't think that's possible, since ints are immutable... it would at 
least be very troublesome. 8/
Do you plan to change the values in Python? If not, create a wrapper 
that returns a list of ints. If you want to change it in Python, you 
will have to create a function setData, that receives a list of ints and 
changes the original array. Notice that this function can be present 
just in the binding, you don't have to code it for the C++ class. This 
interface seems more Pythonic to me. 8)

>In other places still I have a find() function returning a pointer to 
>a single float for example. In this situation I'd want the float to 
>dereference to a float if the pointer is not null, otherwise return 
>none. But if I use a thin wrapper, it can only return float and not 
>none! :(
>

The wonders of Boost.Python (untested):

PyObject* find_wrapper(MyClass* cl)
{
     float *res = cl.find();
     if (res == NULL) {
          Py_INCREF(Py_None);
          return Py_None;
     }
     else {
          return PyFloat_FromDouble((float)v);
     }
}

(I couldn't create a None using Boost Python's api, I tried object(NULL) 
but it didn't work... how can one do that?)

>Lastly, some other methods return a type ** ie; an array of pointers 
>to object instances. How on earth can this get wrapped? Is that 
>indexing suite the right answer for these?
>

I think creating wrappers is the solution here.

Regards,
Nicodemus.