How a DLL Can Display a Message Using MessageBox()

 Last reviewed: July 22, 1997
Article ID: Q22374
3.00 3.10 WINDOWS kbprg

The information in this article applies to:

  • Microsoft Windows Software Development Kit (SDK) for Windows versions 3.1 and 3.0

SUMMARY

In the Microsoft Windows graphical environment, it may be necessary for a function in a dynamic-link library (DLL) to communicate some information to the user. The MessageBox() API is available for this purpose.

MORE INFORMATION

If a function exported from a DLL displays a message box, one of the parameters to the function should be the handle to a window in the application that acts as the parent window for the message box. While the message box is displayed, if Task Manager closes the parent application for the message box, the message box is destroyed.

When a function in a DLL displays a message only in response to an error condition, specify NULL as the value of the hWndParent parameter, as follows: 

   MessageBox(NULL, "Hi there!", "DEMO", MB_OK);
After the user dismisses the dialog box, the focus returns to the window that previously had the focus, as above. However, because the message box has no parent window, closing one or more applications with the Task Manager does not destroy the message box.

Note that the hWndParent parameter must not specify a child window, such as a control in a dialog box. If an appropriate window handle is not readily available, specify NULL for the value of hWndParent and specify the MB_TASKMODAL flag in the wType (fourth) parameter. This prevents the user from interacting with any windows of the current application without suspending other applications.

Additional reference words: 3.00 3.10
KBCategory: kbprg
KBSubcategory: KrDll
Keywords : kb16bitonly

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Last reviewed: July 22, 1997
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