M E N U
Content
Introduction
Release Notes
Features
FAQs
Requirements
Installation
Change Log
Future Plans
Knowledge Base
Reference Manual
Conventions
iPP
Templates
Constants
Identifiers
Operators
Directives
## // /* */
#define
#error
#if{def|ndef}
#include
#message
#undef
Macros
Legal
Feedback
|
Used to control compilation of a block of statements when the specified expression evaluates to true.
Syntax
[ #if expression | #ifdef identifier | #ifndef identifier ]
{ statement }...
{ [ #elif | #elseif ] expression
{ statement }... }...
{#else
{ statement }... }
#endif
Notes
#if
|
Used when evaluating an expression.
|
#ifdef
|
Used to check if an identifier is defined.
|
#ifndef
|
Used to check if an identifier is not defined.
|
#elif
#elseif
|
Used when evaluating an expression. Only evaluated when the preceding
if, elif or elseif directives evaluate to false.
|
#else
|
Used only used when the preceding #if, #ifdef, #ifndef,
#elif or elseif directives evaluate to false.
|
#endif
|
Used to end #if, #ifdef and #ifndef directives.
|
expression
|
the expression to evaluate.
|
identifier
|
the identifier to check for existence.
|
statement
|
the statement(s) to compile when the preceding #if, #ifdef,
#ifndef, #elif or elseif evaluates to true.
|
Example
#ifndef EOF
#define EOF (-1)
#endif
#if VERSION == 1
#include <v1sup.h>
#elif VERSION == 2
#include <v2sup.h>
#elif VERSION == 3
#include <v3sup.h>
#else
#error version not supported
#endif
|