HOWTO: Use the Assert Method for Debugging

ID: Q161153

The information in this article applies to:

Microsoft Visual Basic Learning, Professional, and Enterprise Editions for Windows, version 6.0
Microsoft Visual Basic Control Creation and Enterprise Editions for Windows, version 5.0

SUMMARY

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

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Platform : WINDOWS
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