Header Files in C Programming Language

Header Files in C Programming Language

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Updated on Jun 20, 2023 18:32 IST

The standard pre-defined library functions for the C programming language are contained in header files. By adding a header file using the C preprocessor directive “#include,” you ask for permission to use it in your program.

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The “. h” file extension is used for all header files. In this article, we will discuss more header files, it’s types, ‘include’ operations in C as well as illustrations with examples using C code. 

Table of contents

Header Files in C

A source file with the ‘.h’ extension is a header file. While constants, macros, and system-wide global variables are found in source code, function prototypes, and declarations are found in header files. We just include the header file where the function is declared whenever we need to define a function.

There are 2 types available for header files. They are given below:

  • System-defined header file: System-defined file is a predetermined header file.
  • User-defined header file: User-defined header file is one that has been defined by the user.

You can also explore: Understanding Logical Operators in C

Using the pre-processing directive (#), a program can have both system-defined as well as user-defined header files. The compiler is told to process the files prior to compilation using these preprocessing directives. Two methods exist for including header files:

  • #include<file>
  • #include ‘file’

The header files listed above differ from one another. We can declare the header within angular brackets if the header file is specified in the established source directory.-You can provide the complete path of the header file inside double quotes if it isn’t defined in the pre-defined root directory.

The include function

  • Assume that the header .h comprises of the below declaration:
int *t()
  • The source file will be defined as:
 
#include"header.h"
int main()
{
puts(t());
return 0;
}
Copy code
  • The definition of the header will be replaced by the compiler: 
 
int *t()
int main()
{
puts(t());
return 0;
}
Copy code

You can also explore: C++ Structure and Functions

Explore: Free C++ Courses Online

Check: C++ Online Courses & Certifications

Creating personalized header file

To avoid writing lengthy and complex code, use header files. When we make our own header file, we can then easily utilize it wherever. It improves the functionality and readability of the code.

You can also explore: Ternary Operator in C: Syntax, Examples and Advantages

The steps to make your personalized header file is given as follows:

We’ll start by creating C code and then save it in a file with the ‘.h’ extension. 

 
int multiplytwono(int x, int y)
{
return (x*y);
}
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In the second step, we will create a main program:

 
#include<stdio.h>
#include "multiply.h"
int main()
{
int x=2, y = 3; cout << "The result of multiplication of the two numbers is : "
<< multiplytwono(x, y);
}
Copy code

Common Header Files

  • Use the printf() and scanf() functions to execute input and output operations by including the #include<stdio.h> header file.
  • Use strlen(), strcmp(), and other string-related functions by  #include<string.h> header file.
  • Using the cin and cout objects,  #include<iostream.h> is used to conduct input and output operations.
  • Sqrt(), log2(), pow(), and other predefined math functions are included in this header file through the #include<math.h> directive.
  • #include<iomanip.h> defines the set() and setprecision() functions, which are used to restrict the number of decimal places in variables.
  • #include<signal.h>provides definitions of functions like “signal(),” “raise,” and other ones used to handle signals ().
  • Errno(), strerror(), perror(), and other error handling-related activities are carried out by #include<errno.h>.

You can also epxlore: Learning About Pointers in C

Conclusion

In this article, we have discussed Header Files in C Programming. The standard pre-defined library functions for the C programming language are contained in header files. A source file with the ‘.h’ extension is a header file. We have also discussed the included operation in a header file with example in C code as well as various header files used in C. 

Author: Megha Garg

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FAQs

What are the best practices for working with header files in C?

Here are some best practices: Use header guards to prevent multiple inclusion of the same header file. Keep header files concise and focused on specific functionalities. Avoid including unnecessary headers to minimize dependencies. Use meaningful and descriptive names for functions, structures, and constants defined in the header file. Document the usage and purpose of functions and structures through comments in the header file. By following these practices, you can ensure cleaner and more maintainable code when working with header files in C.

How do I create and use a custom header file in C?

To create a custom header file, you typically create a text file with a .h extension and define the necessary declarations and definitions within it. To use the custom header file in your source code, you include it using the #include directive, providing the file name in double quotes or angle brackets, depending on whether it is a local or system header file, respectively.

Can I create my own header files in C?

Absolutely! You can create your own header files to encapsulate declarations and definitions specific to your project or module. It is a common practice to create header files for custom functions, structures, constants, and other components to promote code reusability and modularity.

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