5.2.3 #IFDEF

Syntax:

#IFDEF name

Lines following #IFDEF are read only if the keyword name following it is defined.

They are read until the keywords #ELSE or #ENDIF are encountered, after which normal processing is resumed.

Example :

#IFDEF VER2_6_0  
-Fu/usr/lib/fpc/2.6.0/linuxunits  
#ENDIF

In the above example, /usr/lib/fpc/2.6.0/linuxunits will be added to the path if you’re compiling with version 2.6.0 of the compiler.