如何用 C++ 爲 Python 寫 dll

如何用 C++ 爲 Python 寫 dll

來自： http://zhongwei-leg.iteye.com/blog/693519

博客分類：
• C++

C C# C++ Python OS 

1. 先新建一個名爲 hello.cpp 的 C++ 源文件：

#include <stdio.h>

#define DLLEXPORT extern "C" __declspec(dllexport)

DLLEXPORT int __stdcall hello()
{
    printf("Hello world!\n");
    return 0;
}

#include <stdio.h>

#define DLLEXPORT extern "C" __declspec(dllexport)

DLLEXPORT int __stdcall hello()
{
    printf("Hello world!\n");
    return 0;
}

 

2. 編譯成 dll 文件：

cl /LD hello.cpp

cl /LD hello.cpp

 

注意， 這裏的參數是 /LD, 而不是 /DL。


3. 編寫一個名爲 hello.py 的 python 文件：

# coding: utf-8

import os
import ctypes

CUR_PATH = os.path.dirname(__file__)

if __name__ == '__main__':
    print 'starting...'
    dll = ctypes.WinDLL(os.path.join(CUR_PATH, 'hello.dll'))
    dll.hello()

# coding: utf-8

import os
import ctypes

CUR_PATH = os.path.dirname(__file__)

if __name__ == '__main__':
    print 'starting...'
    dll = ctypes.WinDLL(os.path.join(CUR_PATH, 'hello.dll'))
    dll.hello()

 

4. 輸出爲：

 

starting...
Hello world!

starting...
Hello world!

 

須要注意的地方：
1. C++ 的 dll 中的接口函數必須以 extern "C" __declspec(dllexport) 爲前綴， C 的以 __declspec(dllexport) 爲前綴。
不然會報錯：

 

Traceback (most recent call last):
  File "hello.py", line 12, in <module>
    dll.hello()
  File "C:\Python25\lib\ctypes\__init__.py", line 361, in __getattr__
    func = self.__getitem__(name)
  File "C:\Python25\lib\ctypes\__init__.py", line 366, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
AttributeError: function 'hello' not found

Traceback (most recent call last):
  File "hello.py", line 12, in <module>
    dll.hello()
  File "C:\Python25\lib\ctypes\__init__.py", line 361, in __getattr__
    func = self.__getitem__(name)
  File "C:\Python25\lib\ctypes\__init__.py", line 366, in __getitem__
    func = self._FuncPtr((name_or_ordinal, self))
AttributeError: function 'hello' not found

 

2. 是使用 ctypes.CDLL 仍是 ctypes.WinDLL 呢？
反正我是分不清，因此在 dll 中的接口函數中顯式地加上了 __stdcall. 彷佛一個是 caller 清棧，另一個是 callee 清。

MSDN 中關於 __stdcall, __cdecl 的介紹：
__cdecl：
http://msdn.microsoft.com/en-us/library/zkwh89ks(VS.80).aspx
This is the default calling convention for C and C++ programs. Because the stack is cleaned up by the caller, it can do vararg functions. The __cdecl calling convention creates larger executables than __stdcall, because it requires each function call to include stack cleanup code. The following list shows the implementation of this calling convention.

__stdcall：
http://msdn.microsoft.com/en-us/library/zxk0tw93(VS.71).aspx
The __stdcall calling convention is used to call Win32 API functions. The callee cleans the stack, so the compiler makes vararg functions __cdecl.

參考文檔：
1. 《How to write a DLL/SO in C/C++ for Python》
http://wolfprojects.altervista.org/dllforpyinc.php

2. 《Python調用windows下DLL詳解 - ctypes庫的使用》
http://blog.csdn.net/magictong/archive/2008/10/14/3075478.aspx