MessageBoxA function (winuser.h)

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 MessageBoxA(
  [in, optional] HWND   hWnd,
  [in, optional] LPCSTR lpText,
  [in, optional] LPCSTR lpCaption,
  [in]           UINT   uType
);

Parameters

[in, optional] hWnd

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.

[in, optional] lpText

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.

[in, optional] lpCaption

Type: LPCTSTR

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

[in] uType

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.

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.

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 will no effect - unless an MB_OK button is present. If an MB_OK button is displayed and the user presses ESC, the return value will be IDOK.

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.

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

See also

Conceptual

Dialog Boxes

FlashWindow

MessageBeep

MessageBoxEx

MessageBoxIndirect

Other Resources

Reference

SetForegroundWindow