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\ -> Commands -> #ifdef

#ifdef

A #ifdef command (like #if and #ifndef) can be used to conditionally include lines of text, this can be any other type of line or command except #elseif or #endif.

#if commands can be nested to any level and there need not be any lines between a #if command and a #endif or #elseif command.

Note that this command only checks on a single variable, for more complex requirements you will need to use a #if command along with calls to the Defined() routine. For performance reasons it is recommended that you use #ifdef and #ifndef commands where possible.

A common use of this command is as a method of creating block comments. Simply specify a variable you know does not exist!

Syntax

[WhiteSpace]#ifdef  MacroName

The "MacroName" specifies the name of a macro that should exist for the test to evaluate to true.

Example #1

#define Fred FredsValue
#ifdef Fred
    ...
#endif

Example #2 - Block Comment

#ifdef DoesNotExist
       <P>This paragraph
       has been commented out
       as we are testing for
       a variable we
       know does not exist.
#endif


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Sunday November 05 2017 at 10:00am