MessageBox
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.
int MessageBox(
|
HWND hWnd, |
// handle of owner
window |
|
LPCTSTR lpText, |
// address of text
in message box |
|
LPCTSTR lpCaption, |
// address of title
of message box |
|
UINT uType |
// style of message
box |
|
); |
|
Parameters
hWnd
Identifies the
owner window of the message box to be created. If this parameter is NULL, the
message box has no owner window.
lpText
Points to a
null-terminated string containing the message to be displayed.
lpCaption
Points to a
null-terminated string used for the dialog box title. If this parameter is
NULL, the default title Error is used.
uType
Specifies a
set of bit flags that determine the contents and behavior of the dialog box.
This parameter can be a combination of flags from the following groups of
flags.
Specify one
of the following flags to indicate the buttons contained in the message box:
|
Flag |
Meaning |
|
MB_ABORTRETRYIGNORE |
The message
box contains three push buttons: Abort, Retry, and Ignore. |
|
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. |
Specify one
of the following flags to display an icon in the message box:
|
Flag |
Meaning |
|
MB_ICONEXCLAMATION,
|
An
exclamation-point icon appears in the message box. |
|
MB_ICONINFORMATION,
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. |
Specify one
of the following flags to indicate the default button:
|
Flag |
Meaning |
|
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. |
Specify one
of the following flags to indicate the modality of the dialog box:
|
Flag |
Meaning |
|
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 applications 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 application. 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
task 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 current application
without suspending other applications. |
In addition,
you can specify the following flags:
MB_DEFAULT_DESKTOP_ONLY
The desktop
currently receiving input must be a default desktop; otherwise, the function
fails. A default desktop is one an application runs on after the user has
logged on.
MB_HELP
Adds a Help
button to the message box. Choosing the Help button or pressing F1 generates a
Help event.
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, Windows 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
only: 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.
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 Windows
NT version 4.0, the value of MB_SERVICE_NOTIFICATION has changed. See WINUSER.H for the old and new values. 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 and MessageBoxEx.
This mapping is only done for executables that have a version number, as set by
the linker, less than 4.0.
To build a
service that uses MB_SERVICE_NOTIFICATION, and can run on both Windows NT 3.x
and Windows NT 4.0, you have two choices.
|
1. At link-time, specify a version number less
than 4.0; or |
|
2. 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. |
MB_SERVICE_NOTIFICATION_NT3X
Windows NT
only: This value corresponds to the
value defined for MB_SERVICE_NOTIFICATION for Windows NT version 3.51.
Return Values
The return
value is zero if there is not enough memory to create the message box.
If the
function succeeds, the return value is one of the following menu-item values
returned by the dialog box:
|
Value |
Meaning |
|
IDABORT |
Abort
button was selected. |
|
IDCANCEL |
Cancel
button was selected. |
|
IDIGNORE |
Ignore
button was selected. |
|
IDNO |
No button was
selected. |
|
IDOK |
OK button
was selected. |
|
IDRETRY |
Retry
button was selected. |
|
IDYES |
Yes button
was selected. |
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.
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.
When an
application calls MessageBox and specifies the MB_ICONHAND and
MB_SYSTEMMODAL flags for the uType parameter, Windows displays the
resulting message box regardless of available memory. When these flags are
specified, Windows limits the length of the message box text to three lines.
Windows does not automatically break the lines to fit in the message
box, however, so the message string must contain carriage returns to break the
lines at the appropriate places.
If you create
a message box while a dialog box is present, use the handle of 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: The system can support a maximum
of 16,364 window handles.
See Also