CreateWindow

The CreateWindow function creates an overlapped, pop-up, or child window. It specifies the window class, window title, window style, and (optionally) the initial position and size of the window. The function also specifies the window's parent or owner, if any, and the window's menu.

To use extended styles in addition to the styles supported by CreateWindow, use the CreateWindowEx function instead of using CreateWindow.

HWND CreateWindow(
  LPCTSTR lpClassName,  // pointer to registered class name
  LPCTSTR lpWindowName, // pointer to 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,          // handle to menu or child-window identifier
  HANDLE hInstance,     // handle to application instance
  LPVOID lpParam        // pointer to window-creation data
);
 

Parameters

lpClassName

Pointer to a null-terminated string or is an integer 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 less than 0xC000, must be in the low-order word of lpClassName; the high-order word must be zero.

If lpClassName is a string, it specifies the window class name. The class name can be any name registered with the RegisterClassEx function or any of the predefined control-class names. For a complete list, see the Remarks section.

lpWindowName

Pointer to a null-terminated string that specifies the window name.

If the window style specifies a title bar, the window title pointed to by lpWindowName is displayed in the title bar. When using CreateWindow to create controls, such as buttons, check boxes, and static controls, use lpWindowName to specify the text of the control.

dwStyle

Specifies the style of the window being created. This parameter can be a combination of the following window styles, plus the control styles indicated in the Remarks section.

Style	Meaning
WS_BORDER	Creates a window that has a thin-line border.
WS_CAPTION	Creates a window that has a title bar (includes the WS_BORDER style).
WS_CHILD	Creates a child window. This style cannot be used with the WS_POPUP style.
WS_CHILDWINDOW	Same as the WS_CHILD style.
WS_CLIPCHILDREN	Excludes the area occupied by child windows when drawing occurs within the parent window. This style is used when creating the parent window.
WS_CLIPSIBLINGS	Clips child windows relative to each other; that is, when a particular child window receives a WM_PAINT message, the WS_CLIPSIBLINGS style clips all other overlapping child windows out of the region of the child window to be updated. If WS_CLIPSIBLINGS is not specified and child windows overlap, it is possible, when drawing within the client area of a child window, to draw within the client area of a neighboring child window.
WS_DISABLED	Creates a window that is initially disabled. A disabled window cannot receive input from the user.
WS_DLGFRAME	Creates a window that has a border of a style typically used with dialog boxes. A window with this style cannot have a title bar.
WS_GROUP	Specifies the first control of a group of controls. The group consists of this first control and all controls defined after it, up to the next control with the WS_GROUP style. The first control in each group usually has the WS_TABSTOP style so that the user can move from group to group. The user can subsequently change the keyboard focus from one control in the group to the next control in the group by using the direction keys.
WS_HSCROLL	Creates a window that has a horizontal scroll bar.
WS_ICONIC	Creates a window that is initially minimized. Same as the WS_MINIMIZE style.
WS_MAXIMIZE	Creates a window that is initially maximized.
WS_MAXIMIZEBOX	Creates a window that has a Maximize button. Cannot be combined with the WS_EX_CONTEXTHELP style. The WS_SYSMENU style must also be specified.
WS_MINIMIZE	Creates a window that is initially minimized. Same as the WS_ICONIC style.
WS_MINIMIZEBOX	Creates a window that has a Minimize button. Cannot be combined with the WS_EX_CONTEXTHELP style. The WS_SYSMENU style must also be specified.
WS_OVERLAPPED	Creates an overlapped window. An overlapped window has a title bar and a border. Same as the WS_TILED style.
WS_OVERLAPPEDWINDOW	Creates an overlapped window with the WS_OVERLAPPED, WS_CAPTION, WS_SYSMENU, WS_THICKFRAME, WS_MINIMIZEBOX, and WS_MAXIMIZEBOX styles. Same as the WS_TILEDWINDOW style.
WS_POPUP	Creates a pop-up window. This style cannot be used with the WS_CHILD style.
WS_POPUPWINDOW	Creates a pop-up window with WS_BORDER, WS_POPUP, and WS_SYSMENU styles. The WS_CAPTION and WS_POPUPWINDOW styles must be combined to make the window menu visible.
WS_SIZEBOX	Creates a window that has a sizing border. Same as the WS_THICKFRAME style.
WS_SYSMENU	Creates a window that has a window-menu on its title bar. The WS_CAPTION style must also be specified.
WS_TABSTOP	Specifies a control that can receive the keyboard focus when the user presses the tab key. Pressing the tab key changes the keyboard focus to the next control with the WS_TABSTOP style.
WS_THICKFRAME	Creates a window that has a sizing border. Same as the WS_SIZEBOX style.
WS_TILED	Creates an overlapped window. An overlapped window has a title bar and a border. Same as the WS_OVERLAPPED style.
WS_TILEDWINDOW	Creates an overlapped window with the WS_OVERLAPPED, WS_CAPTION, WS_SYSMENU, WS_THICKFRAME, WS_MINIMIZEBOX, and WS_MAXIMIZEBOX styles. Same as the WS_OVERLAPPEDWINDOW style.
WS_VISIBLE	Creates a window that is initially visible.
WS_VSCROLL	Creates a window that has a vertical scroll bar.

x

Specifies the initial horizontal position of the window. For an overlapped or pop-up window, the x parameter is the initial x-coordinate of the window's upper-left corner, in screen coordinates. For a child window, x is the x-coordinate of the upper-left corner of the window relative to the upper-left corner of the parent window's client area.

If this parameter is set to CW_USEDEFAULT, the system selects the default position for the window's upper-left corner and ignores the y parameter. CW_USEDEFAULT is valid only for overlapped windows; if it is specified for a pop-up or child window, the x and y parameters are set to zero.

y

Specifies the initial vertical position of the window. For an overlapped or pop-up window, the y parameter is the initial y-coordinate of the window's upper-left corner, in screen coordinates. For a child window, y is the initial y-coordinate of the upper-left corner of the child window relative to the upper-left corner of the parent window's client area. For a list box, y is the initial y-coordinate of the upper-left corner of the list box's client area relative to the upper-left corner of the parent window's client area.

If an overlapped window is created with the WS_VISIBLE style bit set and the x parameter is set to CW_USEDEFAULT, the system ignores the y parameter.

nWidth

Specifies the width, in device units, of the window. For overlapped windows, nWidth is either the window's width, in screen coordinates, or CW_USEDEFAULT. If nWidth is CW_USEDEFAULT, the system selects a default width and height for the window; the default width extends from the initial x-coordinate to the right edge of the screen, and the default height extends from the initial y-coordinate to the top of the icon area. CW_USEDEFAULT is valid only for overlapped windows; if CW_USEDEFAULT is specified for a pop-up or child window, nWidth and nHeight are set to zero.

nHeight

Specifies the height, in device units, of the window. For overlapped windows, nHeight is the window's height, in screen coordinates. If nWidth is set to CW_USEDEFAULT, the system ignores nHeight.

hWndParent

Handle to the parent or owner window of the window being created. To create a child window or an owned window, supply a valid window handle. This parameter is optional for pop-up windows.

Windows NT 5.0 and later: To create a message-only window, supply HWND_MESSAGE or a handle to an existing message-only window.

hMenu

Handle to a menu, or specifies a child-window identifier depending on the window style. For an overlapped or pop-up window, hMenu identifies the menu to be used with the window; it can be NULL if the class menu is to be used. For a child window, hMenu specifies the child-window identifier, an integer value used by a dialog box control to notify its parent about events. The application determines the child-window identifier; it must be unique for all child windows with the same parent window.

hInstance

Handle to the instance of the module to be associated with the window.

lpParam

A pointer to a value to be passed to the window through the CREATESTRUCT structure passed in the lParam parameter the WM_CREATE message. If an application calls CreateWindow to create a multiple document interface (MDI) client window, lpParam must point to a CLIENTCREATESTRUCT structure.

Return Values

If the function succeeds, the return value is a handle to the new window.

If the function fails, the return value is NULL. To get extended error information, call GetLastError.

Remarks

Before returning, CreateWindow sends a WM_CREATE message to the window procedure. For overlapped, pop-up, and child windows, CreateWindow sends WM_CREATE, WM_GETMINMAXINFO, and WM_NCCREATE messages to the window. The lParam parameter of the WM_CREATE message contains a pointer to a CREATESTRUCT structure. If the WS_VISIBLE style is specified, CreateWindow sends the window all the messages required to activate and show the window.

For information on controlling whether the Taskbar displays a button for the created window, see Visibility of Taskbar Buttons.

The following predefined control classes can be specified in the lpClassName parameter. Note the corresponding control styles you can use in the dwStyle parameter.

Windows 95: The system can support a maximum of 16,364 window handles.

Note  If you specify Windows version 4.x when linking your application, its windows cannot have caption buttons unless they also have window menus. This is not a requirement if you specify Windows version 3.x when linking your application.

Windows CE: CreateWindow is implemented as a macro. It is defined as CreateWindowEx, but with the dwExStyle parameter set to 0L.

Menu bars are not supported. The hMenu parameter must be NULL, unless it is used as a child-window identifier.

The MDICLIENT window class is not supported.

The dwStyle parameter can be a combination of the window styles and control styles documented in:

Dialog Boxes

Windows

Controls

The following dwStyle flags are not supported for windows:

The following dwStyle flags are not supported for controls and dialog boxes:

You can use the BS_OWNERDRAW style as a substitute for the BS_USERBUTTON style.

You can use the SS_LEFT or SS_LEFTNOWORDWRAP style instead of the SS_SIMPLE style for static controls..

The MDICLIENT window class is not supported.

All windows implicitly have the WS_CLIPSIBLINGS and WS_CLIPCHILDREN styles.

Windows CE 1.0 does not support owned windows, except for dialog boxes. If the hwndParent parameter is not NULL, the window is implicitly given the WS_CHILD style.

Windows CE version 1.0 does not support menu bars.

QuickInfo

  Windows NT: Requires version 3.1 or later.
  Windows: Requires Windows 95 or later.
  Windows CE: Requires version 1.0 or later.
  Header: Declared in winuser.h.
  Import Library: Use user32.lib.
  Unicode: Implemented as Unicode and ANSI versions on Windows NT.

See Also

Windows Overview, Window Functions, CLIENTCREATESTRUCT, CREATESTRUCT, CreateWindowEx, GlobalAddAtom, RegisterClassEx, WM_COMMAND, WM_CREATE, WM_GETMINMAXINFO, WM_NCCREATE, WM_PAINT