Re: callback from C DLL returning an int [SEC=PERSONAL]

From: RayS

> My ctypes attempt is crashing the wxPython app.
> 
> This is how SetCallback is defined in the DLL:
> 
> extern "C" void __declspec(dllexport) SetCallback( long lAddress )
>   {
>     s_frontend.set_callback((FUNCPTR)lAddress );
>   }
> //The function takes in a 32-bit long pointer to a function. 
> //The function when defined in a calling C program should take in one parameter such as:
> 
> void ASLocalCode::call_back( int iMessage )
> 
> //This is fired when a new block of data is available. iMessage integer value is always 6.
> 
> 
> In Python I did this:
> ______________________________________
> ...
> class myADC:
>   def __init__:
>     ...
>     self.driver = cdll.dataDll
>     ...
>     def data_ready_func(r):
>         print r
> 
>     CB_TYPE = CFUNCTYPE(None, c_int)
>     self.data_ready_ref = CB_TYPE(data_ready_func)
>     print CB_TYPE, self.data_ready_ref
>     self.driver.SetCallback(self.data_ready_ref)
> 
> This prints:
> data_ready_func 6
> then XP pops up a notice "python.exe has encountered a problem"  (the app is still running!), then it all closes with the XP dialog "don't send" button.
> What is wrong here?

The only thing that looks to me like a potential problem is that you don't keep an explicit reference to the callback function - the "def" just creates it at runtime in the scope of the __init__().

I'd try adding something like

  self.callback = data_ready_func

just after defining the callback, to test this theory.

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