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.
C Programming Language
C Programming Language

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.

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


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