/define (Visual Basic)

Defines conditional compiler constants.

' -or-





Required. The symbol to define.


Optional. The value to assign symbol. If value is a string, it must be surrounded by backslash/quotation-mark sequences (\") instead of quotation marks. If no value is specified, then it is taken to be True.


The /define option has an effect similar to using a #Const preprocessor directive in your source file, except that constants defined with /define are public and apply to all files in the project.

You can use symbols created by this option with the #If...Then...#Else directive to compile source files conditionally.

/d is the short form of /define.

You can define multiple symbols with /define by using a comma to separate symbol definitions.

To set /define in the Visual Studio integrated development environment

  1. Have a project selected in Solution Explorer. On the Project menu, click Properties. For more information, see Introduction to the Project Designer.

  2. Click the Compile tab.

  3. Click Advanced.

  4. Modify the value in the Custom Constants box.


The following code defines and then uses two conditional compiler constants.

    ' Vbc /define:DEBUGMODE=True,TRAPERRORS=False test.vb 
    Sub mysub()
#If debugmode Then 
        ' Insert debug statements here.
         MsgBox("debug mode")
        ' Insert default statements here.
#End If 
    End Sub

See Also


#If...Then...#Else Directives

#Const Directive

Sample Compilation Command Lines (Visual Basic)

Other Resources

Visual Basic Command-Line Compiler