Preprocessor in C Language – Introduction of C Preprocessor & its advantages

Introduction to C Preprocessor in C Programming Language

• A preprocessor is a program that processes Source Code before it passes through the compiler for compilation.
• There are some preprocessor commands and directives that are used to instruct Preprocessor and mostly placed at the starting of the C source code.
• To include the various instructions to the compiler in the C source code, some directives are used called as Preprocessor Directives.
• Preprocessor expands the scope of the programming environment.
• Preprocessor commands are executed before the compiler compiles the source code.
• These commands will change the original code according to the operating environment and adds the code that will be required by calls to library functions.

There are 2 main uses of preprocessor directives :

• To include external files such as Header files(stdio.h , math.h etc).
• To define macros.

Preprocessor commands begins with a symbol # as directives.

Example:
A standard input-output header file is written as:
#include <stdio.h>

It is a command which tells the preprocessor to include this external header file as part of the program to be compiled.

• Each preprocessor directive must be on its separate line,

Example:
Wrong:     #include<stdio.h>       #include<math.h>
Correct:   #include<stdio.h>
           #include<math.h>

• To maintain the portability of C programming language in different architectures or compilers,the concept of Preprocessor is introduced.
• All the preprocessor processed before the staring of actual compilation and create an intermediate file.
• In the intermediate file all preprocessor statement/commands are replaced by corresponding C code. During the process of compilation that intermediate file is deleted by the compiler automatically.

Advantages of Preprocessor in C Language

• C Preprocessor improves the readability of C program.
• C  Preprocessor makes the C program easy to maintain.
• C  Preprocessor makes the C program more portable.