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 MessageBox

The MessageBox function creates, displays, and operates a message box. The message box contains an application-defined message and title, along with any combination of predefined icons and push buttons.

Syntax

    int MessageBox(
          HWND hWnd,
          LPCTSTR lpText,
          LPCTSTR lpCaption,
          UINT uType
        );

Parameters

• 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. The question-mark message icon is no longer recommended because it does not clearly represent a specific type of message and because the phrasing of a message as a question could apply to any message type. In addition, users can confuse the message symbol question mark with Help information. Therefore, do not use this question mark message symbol in your message boxes. The system continues to support its inclusion only for backward compatibility.
  • 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 pop-up 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 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 that 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. For information on security considerations in regard to using this flag, see Interactive Services.
  • 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

Adding two right-to-left marks (RLMs), represented by Unicode formatting character U+200F, in the beginning of a MessageBox display string is interpreted by the Win32 MessageBox rendering engine so as to cause the reading order of the MessageBox to be rendered as right-to-left (RTL).

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 preexisting services by mapping the old value to the new value in the implementation of MessageBox. This mapping is done only for executables that have a version number earlier 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 on Windows 95/98/Me Systems to give more consistent behavior across all Windows operating systems.

Function Information

• Minimum DLL Version user32.dll
• Header Declared in Winuser.h, include Windows.h
• Import library User32.lib
• Minimum operating systems Windows 95, Windows NT 3.1
• Unicode Implemented as ANSI and Unicode versions.

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Notebook exported on Monday, 7 July 2008, 18:56:50 PM Eastern Daylight Time