INTRODUCTION:
The C preprocessor, often known as cpp, is a macro processor
that is used automatically by the C compiler to transform your program before
compilation. It is called a macro processor because it allows you to define macros,
which are brief abbreviations for longer constructs.
The C preprocessor is intended to be used only with C, C++, and Objective-C
source code. In the past, it has been abused as a general text processor. It
will choke on input which does not obey C's lexical rules. For example,
apostrophes will be interpreted as the beginning of character constants, and
cause errors. Also, you cannot rely on it preserving characteristics of the
input which are not significant to C-family languages. If a Makefile is preprocessed,
all the hard tabs will be removed, and the Makefile will not work.
Include Syntax
Both user and system header files are
included using the preprocessing directive `#include'.
It has two variants:
#include <file> #include "file" 