| LONG GetWindowLong(hwnd, nOffset) | |||||
| HWND hwnd; | /* handle of window, */ | ||||
| int nOffset; | /* offset of value to retrieve | */ | |||
The GetWindowLong function retrieves a long value at the specified offset into the extra window memory of the given window. Extra window memory is reserved by specifying a nonzero value in the cbWndExtra member of the WNDCLASS structure used with the RegisterClass function.
hwnd
Identifies the window.
nOffset
Specifies the zero-based byte offset of 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 12 or more bytes of extra memory was specified, a value of 8 would be an index to the third long integer), or one of the following values:
| Value | Meaning |
| GWL_EXSTYLE | Extended window style |
| GWL_STYLE | Window style |
| GWL_WNDPROC | Long pointer to the window procedure |
The following values are also available when the hwnd parameter identifies a dialog box:
| Value | Meaning |
| DWL_DLGPROC | Specifies the address of the dialog box procedure. |
| DWL_MSGRESULT | Specifies the return value of a message processed in the dialog box procedure. |
| DWL_USER | Specifies extra information that is private to the application, such as handles or pointers. |
The return value specifies information about the given window if the function is successful.
To access any extra 4-byte values allocated when the window-class structure was created, use a positive byte offset as the index specified by the nOffset parameter, starting at 0 for the first 4-byte value in the extra space, 4 for the next 4-byte value, and so on.