The C Preprocessor
In a macro processor, a conditional is a directive that allows a part of the program to be ignored during compilation, on some conditions. In the C preprocessor, a conditional can test either an arithmetic expression or whether a name is defined as a macro.
A conditional in the C preprocessor resembles in some ways an `if'
statement in C, but it is important to understand the difference between
them. The condition in an `if' statement is tested during the execution
of your program. Its purpose is to allow your program to behave differently
from run to run, depending on the data it is operating on. The condition
in a preprocessing conditional directive is tested when your program is compiled.
Its purpose is to allow different code to be included in the program depending
on the situation at the time of compilation.
The C Preprocessor
Packaging copyright © 1988-2000 OAR Corporation
Context copyright by each document's author. See Free Software Foundation for information.