对于Windows NT 4.0，MB_SERVICE_NOTIFICATION的值己经改变。对于旧的和新的值，请参见WINUSER。
Windows NT 4.O通过把旧值映射到MessageBox和MessageBoxEx执行中的新值，为先存在的服务程序提供逆兼容。此映射只为有了版本数目的可执行程序而做。
为了建立一个用MB_SERVICE_NOTIFICATION的服务器，且可以在Windows NT 3.X和Window NT 4.0上执行，可有两种选择。在连接时间，指定一个版本数目小于4.0的版本，或在连接时间，指定一个4.0版本。在运行时间，用函数GetVersionEx来检测系统版本，然后在Windows NT 3.X上用MB_SERVICE_NOTIFICATION_NT 3.x来运行和在Windows NT 4.0上用MB_SERVICE_NOTIFICAION来运行。MB_SERVCE_NOTIFICATION_NT3.x（WindowNT）此值响应于为WindowNT3.51的MB_SERVICE_NOTIFICAION
The MessageBox function creates, displays, and operates a message box. The message box contains an application-defined message and title, plus any combination of predefined icons and push buttons.
hWnd
[in] Handle to the owner window of the message box to be created. If this parameter is NULL, the message box has no owner window.
lpText
[in] Pointer to a null-terminated string that contains the message to be displayed.
lpCaption
[in] Pointer to a null-terminated string that contains the dialog box title. If this parameter is NULL, the default title Error is used.
uType
[in] Specifies the contents and behavior of the dialog box. This parameter can be a combination of flags from the following groups of flags.
To indicate the buttons displayed in the message box, specify one of the following values.
MB_ABORTRETRYIGNORE
The message box contains three push buttons: Abort, Retry, and Ignore.
MB_CANCELTRYCONTINUE
Microsoft® Windows® 2000/XP: The message box contains three push buttons: Cancel, Try Again, Continue. Use this message box type instead of MB_ABORTRETRYIGNORE.
MB_HELP
Windows 95/98/Me, Windows NT® 4.0 and later: Adds a Help button to the message box. When the user clicks the Help button or presses F1, the system sends a WM_HELP message to the owner.
MB_OK
The message box contains one push button: OK. This is the default.
MB_OKCANCEL
The message box contains two push buttons: OK and Cancel.
MB_RETRYCANCEL
The message box contains two push buttons: Retry and Cancel.
MB_YESNO
The message box contains two push buttons: Yes and No.
MB_YESNOCANCEL
The message box contains three push buttons: Yes, No, and Cancel.
To display an icon in the message box, specify one of the following values.
MB_ICONEXCLAMATION
An exclamation-point icon appears in the message box.
MB_ICONWARNING
An exclamation-point icon appears in the message box.
MB_ICONINFORMATION
An icon consisting of a lowercase letter i in a circle appears in the message box.
MB_ICONASTERISK
An icon consisting of a lowercase letter i in a circle appears in the message box.
MB_ICONQUESTION
A question-mark icon appears in the message box.
MB_ICONSTOP
A stop-sign icon appears in the message box.
MB_ICONERROR
A stop-sign icon appears in the message box.
MB_ICONHAND
A stop-sign icon appears in the message box.
To indicate the default button, specify one of the following values.
MB_DEFBUTTON1
The first button is the default button.
MB_DEFBUTTON1 is the default unless MB_DEFBUTTON2, MB_DEFBUTTON3, or MB_DEFBUTTON4 is specified.
MB_DEFBUTTON2
The second button is the default button.
MB_DEFBUTTON3
The third button is the default button.
MB_DEFBUTTON4
The fourth button is the default button.
To indicate the modality of the dialog box, specify one of the following values.
MB_APPLMODAL
The user must respond to the message box before continuing work in the window identified by the hWnd parameter. However, the user can move to the windows of other threads and work in those windows.
Depending on the hierarchy of windows in the application, the user may be able to move to other windows within the thread. All child windows of the parent of the message box are automatically disabled, but popup windows are not.
MB_APPLMODAL is the default if neither MB_SYSTEMMODAL nor MB_TASKMODAL is specified.
MB_SYSTEMMODAL
Same as MB_APPLMODAL except that the message box has the WS_EX_TOPMOST style. Use system-modal message boxes to notify the user of serious, potentially damaging errors that require immediate attention (for example, running out of memory). This flag has no effect on the user's ability to interact with windows other than those associated with hWnd.
MB_TASKMODAL
Same as MB_APPLMODAL except that all the top-level windows belonging to the current thread are disabled if the hWnd parameter is NULL. Use this flag when the calling application or library does not have a window handle available but still needs to prevent input to other windows in the calling thread without suspending other threads.
To specify other options, use one or more of the following values.
MB_DEFAULT_DESKTOP_ONLY
Windows NT/2000/XP: Same as MB_SERVICE_NOTIFICATION except that the system will display the message box only on the default desktop of the interactive window station. For more information, see Window Stations.
Windows NT 4.0 and earlier: If the current input desktop is not the default desktop, MessageBox fails.
Windows 2000/XP: If the current input desktop is not the default desktop, MessageBox does not return until the user switches to the default desktop.
Windows 95/98/Me: This flag has no effect.
MB_RIGHT
The text is right-justified.
MB_RTLREADING
Displays message and caption text using right-to-left reading order on Hebrew and Arabic systems.
MB_SETFOREGROUND
The message box becomes the foreground window. Internally, the system calls the SetForegroundWindow function for the message box.
MB_TOPMOST
The message box is created with the WS_EX_TOPMOST window style.
MB_SERVICE_NOTIFICATION
Windows NT/2000/XP: The caller is a service notifying the user of an event. The function displays a message box on the current active desktop, even if there is no user logged on to the computer.
Terminal Services: If the calling thread has an impersonation token, the function directs the message box to the session specified in the impersonation token.
If this flag is set, the hWnd parameter must be NULL. This is so the message box can appear on a desktop other than the desktop corresponding to the hWnd.
For more information on the changes between Microsoft® Windows NT® 3.51 and Windows NT 4.0, see Remarks.
MB_SERVICE_NOTIFICATION_NT3X
Windows NT/2000/XP: This value corresponds to the value defined for MB_SERVICE_NOTIFICATION for Windows NT version 3.51.
For more information on the changes between Windows NT 3.51 and Windows NT 4.0, see Remarks.
Return Value
If a message box has a Cancel button, the function returns the IDCANCEL value if either the ESC key is pressed or the Cancel button is selected. If the message box has no Cancel button, pressing ESC has no effect.
If the function fails, the return value is zero. To get extended error information, call GetLastError.
If the function succeeds, the return value is one of the following menu-item values.
IDABORT Abort button was selected.
IDCANCEL Cancel button was selected.
IDCONTINUE Continue button was selected.
IDIGNORE Ignore button was selected.
IDNO No button was selected.
IDOK OK button was selected.
IDRETRY Retry button was selected.
IDTRYAGAIN Try Again button was selected.
IDYES Yes button was selected.
Remarks
When you use a system-modal message box to indicate that the system is low on memory, the strings pointed to by the lpText and lpCaption parameters should not be taken from a resource file, because an attempt to load the resource may fail.
If you create a message box while a dialog box is present, use a handle to the dialog box as the hWnd parameter. The hWnd parameter should not identify a child window, such as a control in a dialog box.
Windows 95/98/Me: The system can support a maximum of 16,364 window handles.
Windows NT/2000/XP: The value of MB_SERVICE_NOTIFICATION changed starting with Windows NT 4.0. Windows NT 4.0 provides backward compatibility for pre-existing services by mapping the old value to the new value in the implementation of MessageBox. This mapping is only done for executables that have a version number less than 4.0, as set by the linker.
To build a service that uses MB_SERVICE_NOTIFICATION, and can run on both Microsoft Windows® NT 3.x and Windows NT 4.0, you can do one of the following.
At link-time, specify a version number less than 4.0
At link-time, specify version 4.0. At run-time, use the GetVersionEx function to check the system version. Then when running on Windows NT 3.x, use MB_SERVICE_NOTIFICATION_NT3X; and on Windows NT 4.0, use MB_SERVICE_NOTIFICATION.
Windows 95/98/Me: Even though MessageBoxW exists, it is supported by the Microsoft Layer for Unicode to give more consistent behavior across all Windows operating systems. To use this, you must add certain files to your application, as outlined in .
Example
For an example, see Displaying a Message Box.
Function Information
Header Declared in Winuser.h, include Windows.h
Import library User32.lib
Minimum operating systems Windows 95, Windows NT 3.1
Unicode Implemented as Unicode and ANSI versions on Windows NT, Windows 2000, Windows XP
