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MessageBox function

Displays a modal dialog box that contains a system icon, a set of buttons, and a brief application-specific message, such as status or error information. The message box returns an integer value that indicates which button the user clicked.

Syntax


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

Parameters

hWnd [in, optional]

Type: HWND

A 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, optional]

Type: LPCTSTR

The message to be displayed. If the string consists of more than one line, you can separate the lines using a carriage return and/or linefeed character between each line.

lpCaption [in, optional]

Type: LPCTSTR

The dialog box title. If this parameter is NULL, the default title is Error.

uType [in]

Type: UINT

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.

ValueMeaning
MB_ABORTRETRYIGNORE
0x00000002L

The message box contains three push buttons: Abort, Retry, and Ignore.

MB_CANCELTRYCONTINUE
0x00000006L

The message box contains three push buttons: Cancel, Try Again, Continue. Use this message box type instead of MB_ABORTRETRYIGNORE.

MB_HELP
0x00004000L

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
0x00000000L

The message box contains one push button: OK. This is the default.

MB_OKCANCEL
0x00000001L

The message box contains two push buttons: OK and Cancel.

MB_RETRYCANCEL
0x00000005L

The message box contains two push buttons: Retry and Cancel.

MB_YESNO
0x00000004L

The message box contains two push buttons: Yes and No.

MB_YESNOCANCEL
0x00000003L

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.

ValueMeaning
MB_ICONEXCLAMATION
0x00000030L

An exclamation-point icon appears in the message box.

MB_ICONWARNING
0x00000030L

An exclamation-point icon appears in the message box.

MB_ICONINFORMATION
0x00000040L

An icon consisting of a lowercase letter i in a circle appears in the message box.

MB_ICONASTERISK
0x00000040L

An icon consisting of a lowercase letter i in a circle appears in the message box.

MB_ICONQUESTION
0x00000020L

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
0x00000010L

A stop-sign icon appears in the message box.

MB_ICONERROR
0x00000010L

A stop-sign icon appears in the message box.

MB_ICONHAND
0x00000010L

A stop-sign icon appears in the message box.

 

To indicate the default button, specify one of the following values.

ValueMeaning
MB_DEFBUTTON1
0x00000000L

The first button is the default button.

MB_DEFBUTTON1 is the default unless MB_DEFBUTTON2, MB_DEFBUTTON3, or MB_DEFBUTTON4 is specified.

MB_DEFBUTTON2
0x00000100L

The second button is the default button.

MB_DEFBUTTON3
0x00000200L

The third button is the default button.

MB_DEFBUTTON4
0x00000300L

The fourth button is the default button.

 

To indicate the modality of the dialog box, specify one of the following values.

ValueMeaning
MB_APPLMODAL
0x00000000L

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
0x00001000L

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
0x00002000L

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.

ValueMeaning
MB_DEFAULT_DESKTOP_ONLY
0x00020000L

Same as desktop of the interactive window station. For more information, see Window Stations.

If the current input desktop is not the default desktop, MessageBox does not return until the user switches to the default desktop.

MB_RIGHT
0x00080000L

The text is right-justified.

MB_RTLREADING
0x00100000L

Displays message and caption text using right-to-left reading order on Hebrew and Arabic systems.

MB_SETFOREGROUND
0x00010000L

The message box becomes the foreground window. Internally, the system calls the SetForegroundWindow function for the message box.

MB_TOPMOST
0x00040000L

The message box is created with the WS_EX_TOPMOST window style.

MB_SERVICE_NOTIFICATION
0x00200000L

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 information on security considerations in regard to using this flag, see Interactive Services. In particular, be aware that this flag can produce interactive content on a locked desktop and should therefore be used for only a very limited set of scenarios, such as resource exhaustion.

 

Return value

Type: int

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.

Return code/valueDescription
IDABORT
3

The Abort button was selected.

IDCANCEL
2

The Cancel button was selected.

IDCONTINUE
11

The Continue button was selected.

IDIGNORE
5

The Ignore button was selected.

IDNO
7

The No button was selected.

IDOK
1

The OK button was selected.

IDRETRY
4

The Retry button was selected.

IDTRYAGAIN
10

The Try Again button was selected.

IDYES
6

The Yes button was selected.

 

Remarks

The following system icons can be used in a message box by setting the uType parameter to the corresponding flag value.

IconFlag values
Icon for MB_ICONHAND, MB_ICONSTOP, and MB_ICONERRORMB_ICONHAND, MB_ICONSTOP, or MB_ICONERROR
Icon for MB_ICONQUESTIONMB_ICONQUESTION
Icon for MB_ICONEXCLAMATION and MB_ICONWARNINGMB_ICONEXCLAMATION or MB_ICONWARNING
Icon for MB_ICONASTERISK and MB_ICONINFORMATIONMB_ICONASTERISK or MB_ICONINFORMATION

 

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 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.

Examples

In the following example, the application displays a message box that prompts the user for an action after an error condition has occurred. The message box displays the message that describes the error condition and how to resolve it. The MB_CANCELTRYCONTINUE style directs MessageBox to provide three buttons with which the user can choose how to proceed. The MB_DEFBUTTON2 style sets the default focus on the second button of the message box, in this case, the Try Again button.


int DisplayResourceNAMessageBox()
{
    int msgboxID = MessageBox(
        NULL,
        (LPCWSTR)L"Resource not available\nDo you want to try again?",
        (LPCWSTR)L"Account Details",
        MB_ICONWARNING | MB_CANCELTRYCONTINUE | MB_DEFBUTTON2
    );

    switch (msgboxID)
    {
    case IDCANCEL:
        // TODO: add code
        break;
    case IDTRYAGAIN:
        // TODO: add code
        break;
    case IDCONTINUE:
        // TODO: add code
        break;
    }

    return msgboxID;
}

The following image shows the output from the preceding code example:

Message box

For another message box example, see Displaying a Message Box.

Requirements

Minimum supported client

Windows 2000 Professional [desktop apps only]

Minimum supported server

Windows 2000 Server [desktop apps only]

Header

Winuser.h (include Windows.h)

Library

User32.lib

DLL

User32.dll

Unicode and ANSI names

MessageBoxW (Unicode) and MessageBoxA (ANSI)

See also

Reference
MessageBoxEx
MessageBoxIndirect
SetForegroundWindow
Conceptual
Dialog Boxes
Other Resources
FlashWindow
MessageBeep

 

 

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