How To Use the Assert Method for Debugging

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Article ID: 161153 - View products that this article applies to.
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The Assert method of the Debug object allows monitoring of an expression for failure conditions.


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 always removes Assert statements from the final code. There is no workaround for this behavior.


Article ID: 161153 - Last Review: July 13, 2004 - Revision: 3.1
  • Microsoft Visual Basic 6.0 Learning Edition
  • Microsoft Visual Basic 6.0 Professional Edition
  • Microsoft Visual Basic 6.0 Enterprise Edition
  • Microsoft Visual Basic 5.0 Control Creation Edition
  • Microsoft Visual Basic 5.0 Enterprise Edition
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