very simple shared dll with ctypes

[Thomas Heller]

mclaugb schrieb:
> I have created a simple windows small_dll.dll exporting a function that does
> a computation using C and C++ classes which i wish to call from Python.  I
> have read lots of ctypes documentation but I still dont quite understand how
> to call the function.
> 
> As a test, I have written a much simpler mathematical function below to try
> to get it to work from Python.
> 
> I am trying to call this from python by:
> 
>>>from ctypes import *
>>>print cdll.small_dll.adder(c_double(5.343534),c_double(3.4432))
>>>2223968
> 
> Can someone give me a few tips to get going!

You should assign the .restype and the .argtypes attributes to your function.
That gives the the proper result, and you don't have to pack the arguments into
c_double yourself.

> The DLL declaration is below.
> 
> #include<windows.h>
> #if defined(_MSC_VER)
> #define DLL extern "C" __declspec(dllexport)
> #else
> #define DLL
> #endif
> 
> DLL double adder(double a, double b){
> double c;
> c=a+b;
> return c;
> }
> 

from ctypes import *
adder = cdll.small_dll.adder
adder.restype = c_double
adder.argtypes = c_double, c_double

print adder(5.343534, 3.4432)


Thomas