如何用 C++ 為 Python 寫 dll

1. 先新建一個名為 hello.cpp 的 C++ 源文件：

Cpp代碼   
#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：

Cpp代碼   
cl /LD hello.cpp  
cl /LD hello.cpp 

注意， 這裡的參數是 /LD, 而不是 /DL。

3. 編寫一個名為 hello.py 的 python 文件：

Python代碼   
# 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. 輸出為：

Python代碼   
starting...   
Hello world!  
starting...
Hello world!

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

Python代碼   
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  www.2cto.com

2. 是使用 ctypes.CDLL 還是 ctypes.WinDLL 呢？
反正我是分不清，所以在 dll 中的接口函數中顯式地加上了 __stdcall. 似乎一個是 caller 清棧，另外一個是 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.