关于GetWindowLong函数的简单问题!

[Jinglihui]

有这样的代码:
LRESULT CALLBACK IwcmServer::WndProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam)
{
CServer *_this = (CServer *) GetWindowLong(hwnd, GWL_USERDATA);
....
}
谁告诉我这是什么目的啊?

[supervar]

对应于
SetWindowLong( int nIndex, LONG dwNewLong );存储4字节到窗口的扩展空间中
GetWindowLong( int nIndex, LONG dwNewLong );得到4字节从窗口的扩展空间中

知道了吧，为什么在IwcmServer类中可以使用CServer的指针了吧！

[superhard]

Retrieves the user data associated with the window. This data is intended for use by the application that created the window. Its value is initially zero.

[fengzi_zhu]

HWND CreateWindow(
LPCTSTR lpClassName, // registered class name
LPCTSTR lpWindowName, // window name
DWORD dwStyle, // window style
int x, // horizontal position of window
int y, // vertical position of window
int nWidth, // window width
int nHeight, // window height
HWND hWndParent, // handle to parent or owner window
HMENU hMenu, // menu handle or child identifier
HINSTANCE hInstance, // handle to application instance
LPVOID lpParam // 【window-creation data】
);