C Headers Tutorial

1. What are Header Files?

Header files in C contain function prototypes, macro definitions, constants, and declarations of variables used in multiple source files. They are included at the beginning of your C programs using the #include directive.

2. Basic Syntax of Header Files

To create a header file, use the .h extension. Here’s an example:

#ifndef HEADER_FILE_NAME_H
#define HEADER_FILE_NAME_H

// Function prototypes and declarations
void printMessage(void);

#endif
                

The #ifndef and #define directives prevent multiple inclusions of the same header file.

3. Including Header Files

To use the header file in a C program, include it with the #include directive:

#include "headerfile.h"
                

Note that quotes are used for custom header files, while <headerfile.h> is used for standard library headers.

4. Example: Using a Header File

Here's a simple example demonstrating the use of header files in C:

// file1.c
#include "myheader.h"
#include <stdio.h>

void printMessage(void) {
    printf("Hello from the header file!\n");
}

int main() {
    printMessage();
    return 0;
}

// myheader.h
#ifndef MYHEADER_H
#define MYHEADER_H

void printMessage(void);

#endif
                

In this example, the printMessage function is declared in the header file myheader.h and used in file1.c.

5. Conclusion

Header files are essential for managing large C projects and organizing reusable code. Proper use of header files improves code maintainability and readability.