Skip to main content

User Defined Header Files in C

User-defined header files​

  • User-defined header files are created by the programmer and are used to share commonly used code between different parts of a program or between different programs.

  • They contains declarations for functions, variables, and other code elements.

  • Header files are used to avoid code repetition, which can save time and reduce errors.

Using User-defined header files​

Creating Header File​

  • Open a text editor or an integrated development environment (IDE).
  • Write the declarations for functions, variables, and other code elements that you want to include in the header file.
  • Save the file with a .h extension.
  • Example: "filename.h"

Using Header File​

  • In the C program where you want to include header file, add the following line at the beginning:
#include "filename.h"
  • Use the functions or variables declared in the header file in your C program as needed.

Example - Using User-defined header files​

Following example illustrates how to create and use a header file:

  • Create a new file called "myheader.h" and add the following declaration to it:
int add(int x, int y);
  • Save the file.
  • Create a new file called "main.c" and add the following code to it
#include "myheader.h"
#include <stdio.h>

int main() {
    int a = 5, b = 10, sum;
    sum = add(a, b);
    printf("The sum of %d and %d is %d\n", a, b, sum);
    return 0;
}
  • Save the file and compile it using a C compiler.
  • Run the program. It should output "The sum of 5 and 10 is 15".

Naming conventions for User-defined header files​

Following are some suggested naming conventions for User-defined header files:

  • Use all lowercase letters: Example "myheader.h"

  • Use underscores to separate words: Example "my_library.h"

  • Use a unique prefix: Good practice for large projects

  • Use a descriptive name: Avoid using generic names like "header.h" or "file.h" and instead use names that describe the contents of the file.