VB.NET Language in a Nutshell, Second Edition

Name

#Const Directive

Syntax

#Const constantname 
                  = 
                  expression

constantname (required; String literal)

Name of the constant

expression (required; literal)

Any combination of literal values, other conditional compilation constants defined with the #Const directive, and arithmetic or logical operators except Is

Description

Defines a conditional compiler constant.

By using compiler constants to create code blocks that are included in the compiled application only when a particular condition is met, you can create more than one version of the application using the same source code. This is a two-step process:

• Defining the conditional compiler constant. This step is optional; conditional compiler constants that are not explicitly defined by the #Const directive, but are referenced in code, default to a value of Nothing.

• Evaluating the constant in the conditional compiler #If...Then statement block.

A conditional compiler constant can be assigned any string, numeric, or logical value returned by an expression. However, the expression itself can only consist of literals, operators other than Is, and another conditional compiler constant.

When the constant is evaluated, the code within the conditional compiler #If... Then block is compiled as part of the application only when the expression using the conditional compiler constant evaluates to True.

Rules at a Glance

• Conditional compiler constants are evaluated by the conditional compiler #If... Then statement block.

• You can use any arithmetic or ...