C language has numerous libraries that include predefined functions to make programming easier.
In C language, header files contain the set of predefined standard library functions. Your request to use a header file in your program by including it with the C preprocessing directive “#include”. All the header file have a ‘.h’ an extension. By including a header file, we can use its contents in our program.
C++ also offers its users a variety of functions, one of which is included in header files. In C++, all the header files may or may not end with the “.h” extension but in C, all the header files must necessarily end with the “.h” extension.
A header file contains:
Function definitions
Data type definitions
Macros
It offers the above features by importing them into the program with the help of a preprocessor directive “#include”. These preprocessor directives are used for instructing compiler that these files need to be processed before compilation.
In C program should necessarily contain the header file which stands for standard input and output used to take input with the help of scanf() and printf() function respectively.
In C++ program has the header file which stands for input and output stream used to take input with the help of “cin” and “cout” respectively.
There are of 2 types of header file:
Pre-existing header files: Files which are already available in C/C++ compiler we just need to import them.
User-defined header files: These files are defined by the user and can be imported using “#include”.
Syntax:
#include <filename.h>
or
#include "filename.h"
We can include header files in our program by using one of the above two syntax whether it is pre-defined or user-defined header file. The “#include” preprocessor is responsible for directing the compiler that the header file needs to be processed before compilation and includes all the necessary data type and function definitions.
Note: We can’t include the same header file twice in any program.
Create your own Header File:
Instead of writing a large and complex code, we can create your own header files and include them in our program to use it whenever we want. It enhances code functionality and readability.
