python对象与C指针对象的转换问题

通过python的ctypes模块调用C函数，常常需要用到用户指针数据指针。如通过python调用Win32 API生成窗口时使用的窗口流程就是一个实例，本文通过这个实例说明如何在python对象和C语言中的指针对象进行相互转换问题。

1、python对象转换为C指针对象

当Python调用SetWindowLong绑定一个Python对象为用户数据时，我们可以如此调用：

from ctypes import *

SetWindowLong= windll.user32.SetWindowLongA

SetWindowLong.restype = c_void_p

SetWindowLong.argtypes = [c_int, c_int, py_object]

CreateWindowEx = windll.user32.CreateWindowExA

CreateWindowEx.argtypes = [c_int,c_char_p,c_char_p,c_int,c_int,c_int,c_int,c_int,c_int,c_int,c_int,c_int]

CreateWindowEx.restype = InvalidHandle

pyObject = py_object(aQWidget) # 转换一个已有的QtWidget对象为pyObject对象，相当于void*指针

hWnd = CreateWindowEx(dwExStyle,szClassName,szWndName,dwStyle,x,y,cx,cy,hWndParent,hMenu,hInstance,0)

SetWindowLong(hWnd,GWL_USERDATA,pyObject ) # 绑定用户数据为void*指针

SetWindowLongPtr(hWnd,GWL_WNDPROC,s_globalWndProcEntryInstance) # Hook窗口流程

2、C指针对象转换为Python对象

当静态窗口流程派发到对象窗口流程时，需要转换void*指针为python对象，我们可以如此调用：

def globalWndProcEntry(hWnd, nMsg, wParam, lParam):

'''全局窗口流程入口'''

# 尝试得到窗口绑定的用户数据

pUserData = GetWindowLongPtr(c_int(hWnd),GWL_USERDATA)

if not pUserData:

if nMsg in (WM_NCCREATE,WM_CREATE):

CreateStruct = cast(lParam, POINTER(CREATESTRUCT)).contents

pUserData = CreateStruct.lpCreateParams

SetWindowLongPtr(c_int(hWnd),GWL_USERDATA,pUserData)

aWindow = cast(pUserData,py_object).value

if hasattr(aWindow,"m_hWnd"):

aWindow.m_hWnd = hWnd

# 处理窗口流程

if pUserData:

aWindow = cast(pUserData,py_object).value

if hasattr(aWindow,"WndProc"):

return aWindow.WndProc(hWnd, nMsg, wParam,lParam)

else:

return DefWindowProc(hWnd,nMsg,wParam,lParam)

else:

return DefWindowProc(hWnd,nMsg,wParam,lParam)

s_globalWndProcEntryInstance = WNDPROC(globalWndProcEntry)