If directive

Format
... ... ...
 * 1) if Val
 * 1) elif Val2
 * 1) else
 * 1) endif

Description
The  statement is used to conditionally compile code. If Val is true (non-zero), the code following the  statement will be compiled. Otherwise, compilation skips to the next ,, or   statement.

defined function
The function  can be used in the conditional expression. It is true if its argument is a defined macro (with ) and false otherwise.

Example // This code will be compiled if DEBUG is // defined // This code will be compiled if DEBUG is // not defined
 * 1) if defined(DEBUG)
 * 1) else
 * 1) endif