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.
Value Meaning - 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.
To indicate the default button, specify one of the following values.
To indicate the modality of the dialog box, specify one of the following values.
To specify other options, use one or more of the following values.
Value Meaning - 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/value | Description |
|---|---|
|
The Abort button was selected. |
|
The Cancel button was selected. |
|
The Continue button was selected. |
|
The Ignore button was selected. |
|
The No button was selected. |
|
The OK button was selected. |
|
The Retry button was selected. |
|
The Try Again button was selected. |
|
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.
| Icon | Flag values |
|---|---|
![]() | MB_ICONHAND, MB_ICONSTOP, or MB_ICONERROR |
![]() | MB_ICONQUESTION |
![]() | MB_ICONEXCLAMATION or MB_ICONWARNING |
![]() | MB_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:

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] |
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Header |
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Library |
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DLL |
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Unicode and ANSI names | MessageBoxW (Unicode) and MessageBoxA (ANSI) |
See also
- Reference
- MessageBoxEx
- MessageBoxIndirect
- SetForegroundWindow
- Conceptual
- Dialog Boxes
- Other Resources
- FlashWindow
- MessageBeep



