ctypes pointer

[mclaugb]

I have a simple function

void adder(double a, double b, double *c){
*c = a+b;
}

i have created a shared dll -- "small_dll4.dll" of it using visual studio.

now i wish to call it from python.
to do so, i have done the following:

libx = cdll("small_dll4.dll", RTLD_GLOBAL)
libx.adder.argtypes = [c_double, c_double, POINTER(c_double)]
libx.adder.restype = None
size=c_double()
zz=libd.adder(3.342, 4, byref(size))

and the result is an access violation!

  File "<console>", line 0, in __main__
WindowsError: exception: access violation reading 0x7EF9DB23

I cant figure out what is causing this.
thanks in advance,
Bryan