Header Files in C

header file is a file with extension .h which contains C function declarations and macro definitions to be shared between several source files. 
 
There are two types of header files: the files that the programmer writes and the files that comes with your compiler.
 
You request to use a header file in your program by including it with the C preprocessing directive #include, like you have seen inclusion of stdio.h header file, which comes along with your compiler.
 
Including a header file is equal to copying the content of the header file but we do not do it because it will be error-prone and it is not a good idea to copy the content of a header file in the source files, especially if we have multiple source files in a program.

A simple practice in C  is that we keep all the constants, macros, system wide global variables, and function prototypes in the header files and include that header file wherever it is required.

Include Syntax
Both the user and the system header files are included using the preprocessing directive #include. It has the following two forms −
#include <file>
This form is used for system header files. It searches for a file named 'file' in a standard list of system directories. You can prepend directories to this list with the -I option while compiling your source code.
#include "file"
This form is used for header files of your own program. It searches for a file named 'file' in the directory containing the current file. You can prepend directories to this list with the -I option while compiling your source code.
 
Once-Only Headers
If a header file happens to be included twice, the compiler will process its contents twice and it will result in an error. The standard way to prevent this is to enclose the entire real contents of the file in a conditional, like this −
#ifndef HEADER_FILE
#define HEADER_FILE
the entire header file file
#endif
This construct is commonly known as a wrapper #ifndef. When the header is included again, the conditional will be false, because HEADER_FILE is defined. The preprocessor will skip over the entire contents of the file, and the compiler will not see it twice.

Comments

Post a Comment

Popular posts from this blog

Programming in C GXEST204 - KTU 2024 scheme syllabus notes pdf ------- Dr Binu V P

About me About the course- Scheme and Evaluation GXEST204 Syllabus GXEST204 Model Question Paper GXEST204 Programming in C - KTU 2024 Scheme University Question Paper GXEST204 Programming in C - KTU 2024 Scheme Introduction to C Programming Beginning with C Programming Programming in C using gcc in Linux Debugging C Program using gdb Module-1 C Fundamentals Structure of a C Program Variables and constants in C Escape Sequences Keywords and Identifiers Data Types and qualifiers   Data Type summary Primitive and Derived Data Type Preprocessor Directive Header Files in C Input-output printf() and scanf() Operators, precedence and expressions Bitwise operators in C Simple Programs to Begin with Control Statements Control statements in C if-else statement , sample programs, programs to try switch case statement, examples, programs to try looping statements, examples, programs to try. Program transfer control statements. Nesting of loops, examples, programs to try. Infinite Loops Mo...
Read more

Structure of a C Program

Image
Lets understand the  basic structure of a C program. A C program is divided into different sections. There are six main sections to a basic c program. The six sections are, Documentation Include/Link/Preprocessor      section Definition Global Declarations ( Functions and variables) Main function Subprogram functions     Now let us learn about each of this layer in detail. Figure: Basic Structure Of C Program Sample Program The C program here will find the area of a circle using a user-defined function and a global variable PI holding the value of pi /* File Name: areaofcircle.c Author: Abhijith date: 06/05/2021   description: a program to calculate area of circle user enters the radius */ #include<stdio.h>    //link section #define PI    3.14;//definition section float area(float r);//global declaration /****************************/ int main()//main function { float r; printf(" Enter the radius:\n"); scanf("%f...
Read more

Files in C

  A file is a repository of data that is store d in a permanent storage media, mainly in secondary memory. In order to use the files we should learn how to read information from a file and how to write information into a file. A very important concept in C is the stream.The stream is a common logical interface to the various devices( files).A stream is linked to a file while using an open operation. A stream is disassociated from a file while using a close operation. The current location, also referred to as the current position, is the location in a file where the next file access will occur.There are two types of streams text and binary. The following are some difference between text and binary files Text file is human readable because everything is stored in terms of text. In binary file everything is written in terms of 0 and 1, therefore binary file is not human readable. A newline(\n) character is converted into the carriage return-linefeed combination before being written to...
Read more