DOCUMENT:Q161153  07-APR-1997  [vbwin]
TITLE   :HOWTO: Use the Assert Method for Debugging
PRODUCT :Microsoft Visual Basic for Windows
PROD/VER:5.0
OPER/SYS:WINDOWS
KEYWORDS:kbusage vb5all vb5howto VBKBDebug kbhowto

======================================================================
---------------------------------------------------------------------
The information in this article applies to:

 - Microsoft Visual Basic Control Creation and Enterprise Edition for
   Windows, version 5.0
---------------------------------------------------------------------

SUMMARY
=======

Microsoft Visual Basic 5.0 introduces a new debugging method for
applications. The Assert method of the Debug object allows monitoring of
an expression for failure conditions.

MORE INFORMATION
================

The following syntax is used for the Assert method:

      Debug.Assert (expression)

The Assert method syntax has the following object qualifier and part:

      Part            Description
      ----            -----------
      Debug           Required. The Assert method only applies to the
                      Debug object.

      expression      Required. Any logical expression.

The Assert method forces a design-time break at the Assert statement when
the expression evaluates to False. If the expression evaluates as True,
program operation continues. For example:

      Function myFunction (x as Long,y as Long, z as Long) as Long
          Debug.Assert (x<>0 And y<>0 And z<>0)
          myFunction = 1/x + 1/y + 1/z
      End Function

If you call myFunction as:

      q = myFunction (1,2,3)

the program continues as normal. However, passing a zero as any one of the
parameters forces a break. The following example breaks at the Assert
statement:

      q = myFunction (1,0,3)

The above example allows testing for inappropriate parameters to protect
against a division by zero error. If a break occurs at the Assert
statement, you can check the locals window to determine which value is
inappropriate. This is especially useful when the argument values come from
other functions:

     q = myFunction ( calcX(), calcY(), calcZ() )

The Assert method is only used for debugging. During compiling, Microsoft
Visual Basic 5.0 always removes Assert statements from the final code.
There is no workaround for this behavior.
======================================================================
Keywords            : kbusage vb5all vb5howto VBKBDebug kbhowto
Version             : 5.0
Platform            : WINDOWS
Issue type          : kbhowto

=============================================================================

THE INFORMATION PROVIDED IN THE MICROSOFT KNOWLEDGE BASE IS
PROVIDED "AS IS" WITHOUT WARRANTY OF ANY KIND.  MICROSOFT DISCLAIMS
ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, INCLUDING THE WARRANTIES
OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.  IN NO
EVENT SHALL MICROSOFT CORPORATION OR ITS SUPPLIERS BE LIABLE FOR
ANY DAMAGES WHATSOEVER INCLUDING DIRECT, INDIRECT, INCIDENTAL,
CONSEQUENTIAL, LOSS OF BUSINESS PROFITS OR SPECIAL DAMAGES, EVEN IF
MICROSOFT CORPORATION OR ITS SUPPLIERS HAVE BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.  SOME STATES DO NOT ALLOW THE EXCLUSION
OR LIMITATION OF LIABILITY FOR CONSEQUENTIAL OR INCIDENTAL DAMAGES
SO THE FOREGOING LIMITATION MAY NOT APPLY.

Copyright Microsoft Corporation 1997.