Writing Python ctypes for Function pointer callback function in C

c, ctypes, python

Solution

Your callback type has the wrong signature; you forgot the result type. It's also getting garbage collected when the function exits; you need to make it global.

Your `GetStatus` call is missing the argument `pArg`. Plus when working with pointers you need to define `argtypes`, else you'll have problems on 64-bit platforms. ctypes' default argument type is a C `int`.

from ctypes import * 

api = CDLL('API.dll')
StatusCB = WINFUNCTYPE(None, c_int, c_int, c_void_p)

GetStatus = api.GetStatus
GetStatus.argtypes = [StatusCB, c_void_p]
GetStatus.restype = None

def status_fn(nErrorCode, nSID, pArg):        
    print 'Hello world'
    print pArg[0]  # 42?

# reference the callback to keep it alive
_status_fn = StatusCB(status_fn)

arg = c_int(42) # passed to callback?    

def start():        
    GetStatus(_status_fn, byref(arg))

Problem

I am trying to write python code to call dll functions and stuck at the function below, which I believe is related to the typedef callback function or the function pointer thing. I have tested the code below, when the callback function is called, python crashes (Window notification-- python.exe has stop responding) with no debug msg. I am deeply confused, any help will be appreciated :) Thanks! C: ``` #ifdef O_Win32 /** @cond */ #ifdef P_EXPORTS #define API __declspec(dllexport) #else #define API __declspec(dllimport) #endif // #ifdef P_EXPORTS /** @endcond */ #endif // #ifdef O_Win32 // Type definition typedef void (__stdcall *StatusCB)(int nErrorCode, int nSID, void *pArg); //Function void GetStatus(StatusCB StatusFn, void *pArg); ``` Python: ``` from ctypes import * def StatusCB(nErrorCode, nSID, pArg): print 'Hello world' def start(): lib = cdll.LoadLibrary('API.dll') CMPFUNC = WINFUNCTYPE(c_int, c_int, c_void_p) cmp_func = CMPFUNC(StatusCB) status_func = lib.GetStatus status_func(cmp_func) ```

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