GetWindowLong函數詳解

函數功能描述:用這個函數能夠獲得指定視窗的資訊

函數原型：
LONG GetWindowLong( HWND hWnd,int nIndex )

參數：
hWnd：指定視窗的控制代碼
nIndex：需要獲得的資訊的類型
     值            功能

nIndex取值如下:
GWL_EXSTYLE    得到擴充的視窗風格
GWL_STYLE      得到視窗風格
GWL_WNDPROC    得到視窗回呼函數的地址，或者控制代碼。得到後必須使用CallWindowProc函數來調用
GWL_HINSTANCE  得到應用程式運行執行個體的控制代碼
GWL_HWNDPARENT 得到父視窗的控制代碼
GWL_ID         得到視窗的標識符
GWL_USERDATA   得到和視窗相關聯的32位的值（每一個視窗都有一個有意留給建立視窗的應用程式是用的32位
               的值）

當hWnd標識一個對話方塊時可以使用下面的值
Value Action
DWL_DLGPROC   得到對話方塊回呼函數的地址，或者控制代碼。得到後必須使用CallWindowProc函數來調用
DWL_MSGRESULT 得到對話方塊回呼函數中訊息處理過程的傳回值
DWL_USER      得到額外的應用程式私人資訊，如一些控制代碼和指標等

傳回值：
成功時，返回一個請求的32位的值
失敗時，返回0，可以使用GetLastError來取得錯誤資訊

 MSDN的原文:

GetWindowLong

The GetWindowLong function retrieves information about the specified window. The function also retrieves the 32-bit (long) value at the specified offset into the extra window memory of a window.

LONG GetWindowLong( HWND hWnd, // handle of window int nIndex  // offset of value to retrieve); 

Parameters

hWnd

Handle to the window and, indirectly, the class to which the window belongs.

nIndex

Specifies the zero-based offset to the value to be retrieved. Valid values are in the range zero through the number of bytes of extra window memory, minus four; for example, if you specified 12 or more bytes of extra memory, a value of 8 would be an index to the third 32-bit integer. To retrieve any other value, specify one of the following values:

Value	Action
GWL_EXSTYLE	Retrieves the extended window styles.
GWL_STYLE	Retrieves the window styles.
GWL_WNDPROC	Retrieves the address of the window procedure, or a handle representing the address of the window procedure. You must use the CallWindowProc function to call the window procedure.
GWL_HINSTANCE	Retrieves the handle of the application instance.
GWL_HWNDPARENT	Retrieves the handle of the parent window, if any.
GWL_ID	Retrieves the identifier of the window.
GWL_USERDATA	Retrieves the 32-bit value associated with the window. Each window has a corresponding 32-bit value intended for use by the application that created the window.

The following values are also available when the hWnd parameter identifies a dialog box:

Value	Action
DWL_DLGPROC	Retrieves the address of the dialog box procedure, or a handle representing the address of the dialog box procedure. You must use the CallWindowProc function to call the dialog box procedure.
DWL_MSGRESULT	Retrieves the return value of a message processed in the dialog box procedure.
DWL_USER	Retrieves extra information private to the application, such as handles or pointers.

Return Values

If the function succeeds, the return value is the requested 32-bit value.

If the function fails, the return value is zero. To get extended error information, callGetLastError.