Header Files in C

Hello everyone, This is my first post to dev.to in which I’m excited to share some insights on Header Files in C. I hope you find this discussion useful and informative

The C language is famous for its various libraries and predefined functions pre-written within it. These make the programmer's effort a lot easier.

What are the Header Files
Header files are additional files in a C language containing definitions of different functions and their associated variables that need to be imported into a C program with the help of a preprocessor #include statement. All the header files have a '.h' extension that contains C function declarations and macro definitions. The default header file that comes with the C compiler is the stdio.h.

  The basic syntax of using these header files is:
  #include<stdio.h>

There are two types of header files in C

1. Standard Header Files in C
2. User-defined Header Files in C

Standard Header Files in C

Standard header files contain the libraries defined in the ISO standard of the C programming language. They are stored in the default directory of the compiler and are present in all the C compilers from any vendor.
There are 31 standard header files in the latest version of C language.

Let’s have a look at some standard header files to have a better understanding:

 - <stdio.h>    : The very basic one which enables input and output.
 - <math.h>     : Allows us to use the Mathematical functions
 - <conio.h>    : Has certain in-built functions like clrscr(), getch(), etc.
 - <complex.h>  : Complex number arithmetic
 - <float.h>    : Contains constants related to floating point values.
 - <tgmath.h>   : Combines math.h and complex.h
 - <time.h>     : time/date utilities
 - <stdbool.h>  : Boolean datatype
 - <signal.h>   : Signal handling

User-defined Header Files in C

User-defined header file is self-explanatory. C language offers a feature that enables us to create a header file and includes it in our code.
User-defined header files in C enable you to declare functions, macros, and types that can be shared across multiple source files, enhancing modularity and code reusability. These files typically have a .h extension and contain declarations, while the corresponding definitions are placed in .c files.

• Header File Creation:
  Create a .h header file (e.g., my_header.h) and add function prototypes, macros, and type definitions. Use include guards (#ifndef, #define, #endif) to prevent multiple inclusions, which could lead to errors.
  Example:

   #ifndef MY_HEADER_H
   #define MY_HEADER_H
  
   void myFunction();
   #define PI 3.14159
   typedef struct {
     int x;
     int y;
     } Point;
  
    #endif
  

• Including the Header:

In your source files, include the header using #include "my_header.h". This allows you to access the declared functions, macros, and types.

• Function Definitions:

Implement the functions declared in the header within a .c file (e.g., my_functions.c).
Example:

 #include "my_header.h"

 void myFunction() {
    printf("Function defined in a user-defined header file.\n");
 }

• Compilation:

Compile the source files together (e.g., gcc main.c my_functions.c -o my_program), linking the code to create an executable.

Comments

[Paul J. Lucas]

A better article is here.