Use CUserException when you want to use the throw/catch exception mechanism for application-specific exceptions. "User" in the class name can be interpreted as "my user did something exceptional that I need to handle."

A CUserException is usually thrown after calling the global function AfxMessageBox to notify the user that an operation has failed. When you write an exception handler, handle the exception specially since the user usually has already been notified of the failure. The framework throws this exception in some cases. To throw a CUserException yourself, alert the user and then call the global function AfxThrowUserException.

In the example below, a function containing operations that may fail alerts the user and throws a CUserException. The calling function catches the exception and handles it specially:

void DoSomeOperation( )
{
    // Processing
    // If something goes wrong...
    AfxMessageBox( "The x operation failed" );
    AfxThrowUserException( );
}

BOOL TrySomething( )
{
    TRY
    {
        // Could throw a CUserException or other exception.
        DoSomeOperation( ); 
    }
    CATCH( CUserException, e )
    {
        return FALSE;    // User already notified.
    }
    AND_CATCH( CException, e )
    {
        // For other exception types, notify user here.
        AfxMessageBox( "Some operation failed" );
        return FALSE;
    }
    END_CATCH
    return TRUE;   // No exception thrown.
}

For more information on using CUserException, see the article Exception Handling (MFC).

Header: afxwin.h

Reference

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