Perhaps I should look into Cython as I'm currently working on a
project that utilises a C API.
I've been finding that getting the data types to be exactly what the C
API is expecting to be the hardest part.
With the original question in mind, here's an example calling into a
C++ external C API:
(Works if compiled is VisualStudio. The DLL produced by MinGW-G++ didn't work).
-------------------------------
// main.h
#ifndef __MAIN_H__
#define __MAIN_H__
#include <windows.h>
#define DLL_EXPORT __declspec(dllexport)
#ifdef __cplusplus
extern "C"
{
#endif
int DLL_EXPORT add(int a, int b);
#ifdef __cplusplus
}
#endif
#endif // __MAIN_H__
-------------------------------
-------------------------------
//main.cpp
#include "main.h"
// a sample exported function
int DLL_EXPORT add(int a, int b)
{
return(a + b);
}
extern "C" DLL_EXPORT BOOL APIENTRY DllMain(HINSTANCE hinstDLL, DWORD
fdwReason, LPVOID lpvReserved)
{
switch (fdwReason)
{
case DLL_PROCESS_ATTACH:
// attach to process
// return FALSE to fail DLL load
break;
case DLL_PROCESS_DETACH:
// detach from process
break;
case DLL_THREAD_ATTACH:
// attach to thread
break;
case DLL_THREAD_DETACH:
// detach from thread
break;
}
return TRUE; // succesful
}
-------------------------------
-------------------------------
# -*- coding: utf-8 -*-
# dll.py
import ctypes
class DllInterface(object):
dll_handle = None
def __init__(self, dll_file):
self.dll_handle = ctypes.WinDLL(dll_file)
def add_a_and_b(self, a=0, b=0):
return self.dll_handle.add(a, b)
if __name__ == '__main__':
dll_file = 'PythonDLL.dll'
external_lib = DllInterface(dll_file)
int_a = ctypes.c_int(1)
int_b = ctypes.c_int(2)
result = external_lib.add_a_and_b(int_a, int_b)
print(result)
-------------------------------
--
James
--
James
On 13 March 2014 15:57, Stefan Behnel <stefan...@behnel.de> wrote:
> Alan Gauld, 12.03.2014 23:05:
>> On 12/03/14 16:49, Stefan Behnel wrote:
>>> Alan Gauld, 12.03.2014 10:11:
>>>> If it were a library then you would have to call
>>>> the individual C++ functions directly using
>>>> something like ctypes, which is usually more
>>>> complex.
>>>
>>> ctypes won't talk to C++, but Cython can do it quite easily.
>>
>> I thought it would work provided the interface functions
>> were declared as C functions? That might involve
>> writing a wrapper around it but that is usually
>> trivial if you have to compile the source anyway.
>
> The thing is: if you have to write your own wrapper anyway (trivial or
> not), then why not write it in Cython right away and avoid the intermediate
> plain C level?
>
> It's usually much nicer to work with object oriented code on both sides
> (assuming you understand the languages on both sides), than to try to
> squeeze them through a C-ish API bottleneck in the middle.
>
> Stefan
>
>
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