C Header Files

In C Programming Language Header Files gives us way to reuse the external declarations, functions or macro definition and allows us to share between other source files.When you include a header file, the compiler adds the functions, data types, and other information in the header file to the list of reserved words and commands in the language. We can include a header file in our program using C Preprocessor Directive “#include”, Header files almost always have a .h extension.Including header file produces the same result as you copy the source code in your program.

In C Programming Language Headers file are used for following purpose –

  • It enables you to include system or operating system related macro definition and function, so that you can invoke system calls and libraries.
  • You can create your own custom header files so that you can reuse and share it.
  • It makes program more manageable.
  • It increase the portability of program.

One of the most commonly used header file is for the standard input/output routines is called stdio.h.

We can include header files in following two ways –

includes a header file from the current directory (the directory in which your C source code file appears), and

includes a file from a system directory.

Type Of Header Files

Standard Header Files

It is the set of header files those used for performing various common and standard operations.

stdio.h – Defines core input and output functions

string.h – Defines string handling functions.

time.h – Defines date and time handling functions

math.h – Defines common mathematical functions.

User Defined Header Files

In C Programming Language user can have their own custom header file that provide additional capabilities.

How to Create Your Own Header File in C Programming Language

Step #1

Type the below source code in a file

Put only function definition as you write in General C Program

Step #2

  • Save Above Code with [.h ] Extension .
  • Let name of our header file be myhead [ myhead.h ]
  • Compile Code if required.

Step #3

Write Main Program

  • Include Our New Header File .
  • Instead of writing < myhead.h> use this terminology “myhead.h”
  • All the Functions defined in the myhead.h header file are now ready for use .
  • Directly call function add(); [ Provide proper parameter and take care of return type ]

While running your program both files (myhead.h and sample.c) should be in same directory.