WNDCLASS info Overview Group

The WNDCLASS structure contains the window class attributes that are registered by the RegisterClass function.

typedef struct _WNDCLASS {    // wc 

    UINT    style; 

    WNDPROC lpfnWndProc; 

    int     cbClsExtra; 

    int     cbWndExtra; 

    HANDLE  hInstance; 

    HICON   hIcon; 

    HCURSOR hCursor; 

    HBRUSH  hbrBackground; 

    LPCTSTR lpszMenuName; 

    LPCTSTR lpszClassName; 

} WNDCLASS;

Members

style

Specifies the class style(s). Styles can be combined by using the bitwise OR (|) operator. This member can be any combination of the following values:

Value	Action
CS_BYTEALIGNCLIENT	Aligns the window’s client area on the byte boundary (in the x direction) to enhance performance during drawing operations. This style affects the width of the window and its horizontal position on the display.
CS_BYTEALIGNWINDOW	Aligns a window on a byte boundary (in the x direction) to enhance performance during operations that involve moving or sizing the window. This style affects the width of the window and its horizontal position on the display.
CS_CLASSDC	Allocates one device context to be shared by all windows in the class. Because window classes are process specific, it is possible for multiple threads of a multithreaded application to create a window of the same class. It is also possible for the threads to attempt to use the device context simultaneously. When this happens, the operating system allows only one of the threads to successfully finish its drawing operation.
CS_DBLCLKS	Sends double-click messages to the window procedure when the user double-clicks the mouse while the cursor is within a window belonging to the class.
CS_GLOBALCLASS	Allows an application to create a window of the class regardless of the value of the hInstance parameter passed to the CreateWindow or CreateWindowEx function. If you do not specify this style, the hInstance parameter passed to the CreateWindow (or CreateWindowEx) function must be the same as the hInstance parameter passed to the RegisterClass function.
	You can create a global class by creating the window class in a dynamic-link library (DLL) and listing the name of the DLL in the registry under the following keys:
	HKEY_LOCAL_MACHINE\Software \Microsoft\Windows NT\ CurrentVersion\Windows\APPINIT_DLLS
	Whenever a process starts, the operating system loads the specified DLLs in the context of the newly started process before calling the main function in that process. The DLL must register the class during its initialization procedure and must specify the CS_GLOBALCLASS style.
CS_HREDRAW	Redraws the entire window if a movement or size adjustment changes the width of the client area.
CS_NOCLOSE	Disables the Close command on the System menu.
CS_OWNDC	Allocates a unique device context for each window in the class.
CS_PARENTDC	Sets the clipping region of the child window to that of the parent window so that the child can draw on the parent. A window with the CS_PARENTDC style bit receives a regular device context from the system’s cache of device contexts. It does not give the child the parent’s device context or device context settings. Specifying CS_PARENTDC enhances an application’s performance.
CS_SAVEBITS	Saves, as a bitmap, the portion of the screen image obscured by a window. Windows uses the saved bitmap to re-create the screen image when the window is removed. Windows displays the bitmap at its original location and does not send WM_PAINT messages to windows obscured by the window if the memory used by the bitmap has not been discarded and if other screen actions have not invalidated the stored image. This style is useful for small windows (for example, menus or dialog boxes) that are displayed briefly and then removed before other screen activity takes place. This style increases the time required to display the window, because the operating system must first allocate memory to store the bitmap.
CS_VREDRAW	Redraws the entire window if a movement or size adjustment changes the height of the client area.

lpfnWndProc

Points to the window procedure. You must use the CallWindowProc function to call the window procedure. For more information, see WindowProc.

cbClsExtra

Specifies the number of extra bytes to allocate following the window-class structure. The operating system initializes the bytes to zero.

cbWndExtra

Specifies the number of extra bytes to allocate following the window instance. The operating system initializes the bytes to zero. If an application uses the WNDCLASS structure to register a dialog box created by using the CLASS directive in the resource file, it must set this member to DLGWINDOWEXTRA.

hInstance

Identifies the instance that the window procedure of this class is within.

hIcon

Identifies the class icon. This member must be a handle of an icon resource. If this member is NULL, an application must draw an icon whenever the user minimizes the application’s window.

hCursor

Identifies the class cursor. This member must be a handle of a cursor resource. If this member is NULL, an application must explicitly set the cursor shape whenever the mouse moves into the application’s window.

hbrBackground

Identifies the class background brush. This member can be a handle to the physical brush to be used for painting the background, or it can be a color value. A color value must be one of the following standard system colors (the value 1 must be added to the chosen color). If a color value is given, you must convert it to one of the following HBRUSH types:

COLOR_ACTIVEBORDER
COLOR_ACTIVECAPTION
COLOR_APPWORKSPACE
COLOR_BACKGROUND
COLOR_BTNFACE
COLOR_BTNSHADOW
COLOR_BTNTEXT
COLOR_CAPTIONTEXT
COLOR_GRAYTEXT
COLOR_HIGHLIGHT
COLOR_HIGHLIGHTTEXT
COLOR_INACTIVEBORDER
COLOR_INACTIVECAPTION
COLOR_MENU
COLOR_MENUTEXT
COLOR_SCROLLBAR
COLOR_WINDOW
COLOR_WINDOWFRAME
COLOR_WINDOWTEXT

The operating system automatically deletes class background brushes when the class is freed. An application should not delete these brushes, because a class may be used by multiple instances of an application.

When this member is NULL, an application must paint its own background whenever it is requested to paint in its client area. To determine whether the background must be painted, an application can either process the WM_ERASEBKGND message or test the fErase member of the PAINTSTRUCT structure filled by the BeginPaint function.

lpszMenuName

Points to a null-terminated character string that specifies the resource name of the class menu, as the name appears in the resource file. If you use an integer to identify the menu, use the MAKEINTRESOURCE macro. If this member is NULL, windows belonging to this class have no default menu.

lpszClassName

Points to a null-terminated string or is an atom. If this parameter is an atom, it must be a global atom created by a previous call to the GlobalAddAtom function. The atom, a 16-bit value, must be in the low-order word of lpszClassName; the high-order word must be zero.

If lpszClassName is a string, it specifies the window class name.

WNDCLASS info Overview Group

Members

See Also