Monday, 29 February 2016
The C Preprocessor is
not a part of the compiler, but is a separate step in the compilation process.
In simple terms, a C Preprocessor is just a text substitution tool and it
instructs the compiler to do required pre-processing before the actual
compilation. We'll refer to the C Preprocessor as CPP.
All
preprocessor commands begin with a hash symbol (#). It must be the first
nonblank character, and for readability, a preprocessor directive should begin
in the first column. The following section lists down all the important preprocessor
directives −
|
Directive
|
Description
|
|
#define
|
Substitutes
a preprocessor macro.
|
|
#include
|
Inserts
a particular header from another file.
|
|
#undef
|
Undefines
a preprocessor macro.
|
|
#ifdef
|
Returns
true if this macro is defined.
|
|
#ifndef
|
Returns
true if this macro is not defined.
|
|
#if
|
Tests
if a compile time condition is true.
|
|
#else
|
The
alternative for #if.
|
|
#elif
|
#else
and #if in one statement.
|
|
#endif
|
Ends
preprocessor conditional.
|
|
#error
|
Prints
error message on stderr.
|
|
#pragma
|
Issues
special commands to the compiler, using a standardized method.
|
example: #include<stdio.h>
Basic example showing constants usage in C
ReplyDeletec codings