Conditional compilation

Syntax 1

&ifdef identifier
...
[&else
...]
&endif

Syntax 2

&ifndef identifier
...
[&else
...]
&endif

identifier is a preprocessor constant.

Usage

The &ifdef and &ifndef preprocessor macros can be used to integrate code lines conditionally according to the existence of a preprocessor constant.

The constant is defined with a &define or with the -D option in the command line.

Even if the condition is evaluated to false, the content of the &ifdef block is still scanned and tokenized. Therefore, it must be lexically correct.

Sometimes it is useful to use some code if a macro is not defined. You can use &ifndef, that evaluates to true if the macro is not defined.

Source: File A

&define IS_DEFINED
&ifdef IS_DEFINED
DISPLAY "The macro is defined"
&endif  /* IS_DEFINED */

Result:

& 1 "A"


DISPLAY "The macro is defined"