#If...Then...#Else Directive

       

Conditionally compiles selected blocks of Visual Basic code.

Syntax

#If expression Then

statements

[#ElseIf expression-n Then

[elseifstatements]]

[#Else

[elsestatements]]

#End If

The #If...Then...#Else directive syntax has these parts:

Part	Description
expression	Required. Any expression, consisting exclusively of one or more conditional compiler constants, literals, and operators, that evaluates to True or False.
statements	Required. Visual Basic program lines or compiler directives that are evaluated if the associated expression is True.
expression-n	Optional. Any expression, consisting exclusively of one or more conditional compiler constants, literals, and operators, that evaluates to True or False.
elseifstatements	Optional. One or more program lines or compiler directives that are evaluated if expression-n is True.
elsestatements	Optional. One or more program lines or compiler directives that are evaluated if no previous expression or expression-n is True.

Remarks

The behavior of the #If...Then...#Else directive is the same as the If...Then...Else statement, except that there is no single-line form of the #If, #Else, #ElseIf, and #End If directives; that is, no other code can appear on the same line as any of the directives. Conditional compilation is typically used to compile the same program for different platforms. It is also used to prevent debugging code from appearing in an executable file. Code excluded during conditional compilation is completely omitted from the final executable file, so it has no size or performance effect.

Regardless of the outcome of any evaluation, all expressions are evaluated. Therefore, all constants used in expressions must be defined — any undefined constant evaluates as Empty.

Note   The Option Compare statement does not affect expressions in #If and #ElseIf statements. Expressions in a conditional-compiler directive are always evaluated with Option Compare Text.