Re: The newbie's question about wrapping c++ class with pyrex

On Apr 17, 2008, at 6:47 PM, Yong Sun wrote:

> Hi, experts,
>
> I am following the tutorial at http://wiki.cython.org/ 
> WrappingCPlusPlus, and found a minor issue,
>
> cdef class Rectangle:
>  - c_Rectangle *thisptr # hold a C++ instance which we're wrapping
>  + cdef c_Rectangle *thisptr # hold a C++ instance which we're  
> wrapping

Thanks. I've made this change on the Cython wiki. I also corrected an  
error about operator overloading.

I'd like to add this example to the automated testing infrastructure,  
but it seems unclear how to do so with the current runtests.py.

>
> I need the above change to make it successfully compiled by cython.  
> While, when I tried to compile it with pyrexc, I met following errors,
>
> $ pyrexc --cplus rect.pyx
> rect.pyx:4:21: Non-extern C function declared but not defined
> rect.pyx:5:21: Non-extern C function declared but not defined
> rect.pyx:6:19: Non-extern C function declared but not defined
> rect.pyx:7:17: Non-extern C function declared but not defined
> rect.pyx:18:27: Object of type 'c_Rectangle' has no attribute  
> 'getLength'
> rect.pyx:20:27: Object of type 'c_Rectangle' has no attribute  
> 'getHeight'
> rect.pyx:22:27: Object of type 'c_Rectangle' has no attribute  
> 'getArea'
> rect.pyx:24:20: Object of type 'c_Rectangle' has no attribute 'move'
>
> BTW, I am using the latest stable version,
>
> $ pyrexc --version
> Pyrex version 0.9.6.4

In Pyrex you need to declare functions as function pointers, i.e.

cdef extern from "Rectangle.h":
     ctypedef struct c_Rectangle "Rectangle":
         int x0, y0, x1, y1
         (int *getLength)()
         ...

>
> Thank you very much!
>
> Regards,
>
>
>
> cdef extern from "Rectangle.h":
>     ctypedef struct c_Rectangle "Rectangle":
>         int x0, y0, x1, y1
>         int getLength()
>         int getHeight()
>         int getArea()
>         void move(int dx, int dy)
>     c_Rectangle *new_Rectangle "new Rectangle" (int x0, int y0, int  
> x1, int y1)
>     void del_Rectangle "delete" (c_Rectangle *rect)
>
> cdef class Rectangle:
>     cdef c_Rectangle *thisptr      # hold a C++ instance which  
> we're wrapping
>     def __cinit__(self, int x0, int y0, int x1, int y1):
>         self.thisptr = new_Rectangle(x0, y0, x1, y1)
>     def __dealloc__(self):
>         del_Rectangle(self.thisptr)
>     def getLength(self):
>         return self.thisptr.getLength()
>     def getHeight(self):
>         return self.thisptr.getHeight()
>     def getArea(self):
>         return self.thisptr.getArea()
>     def move(self, dx, dy):
>         self.thisptr.move(dx, dy)
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