Information Technology Reference
In-Depth Information
Conditional Compilation
Conditional compilation allows you to mark a section of source code to be either compiled or
skipped, depending on whether a particular compilation symbol is defined.
There are four directives for specifying conditional compilation:
#if
#else
#elif
#endif
A
condition
is a simple expression that returns either
true
or
false
.
A condition can consist of a single compilation symbol, or an expression of symbols
and operators, as summarized in Table 22-2. Sub-expressions can be grouped with
parentheses.
The literals
true
and
false
can also be used in conditional expressions.
Table 22-2.
Conditions Used in the #if and #elif Directives
True
: If the symbol has been defined
using a
#define
directive.
False: Otherwise.
Compilation
symbol
Identifier, defined (or not) using the
#define
directive.
True
: If the expression evaluates to
true
.
False: Otherwise.
Expression
Constructed using symbols and the
operators:
!
,
==
,
!=
,
&&
,
||
The following are examples of conditional compilation conditions.
Expression
↓
#if !DemoVersion
...
#endif
Expression
↓
#if (LeftHanded && OemVersion) || FullVersion
...
#endif
#if true // The following code segment will always be compiled.
...
#endif
