Do you really understand #include?

PublishedDecember 24, 2023

I am Jyotiprakash, a deeply driven computer systems engineer, software developer, teacher, and philosopher. With a decade of professional experience, I have contributed to various cutting-edge software products in network security, mobile apps, and healthcare software at renowned companies like Oracle, Yahoo, and Epic. My academic journey has taken me to prestigious institutions such as the University of Wisconsin-Madison and BITS Pilani in India, where I consistently ranked among the top of my class.

At my core, I am a computer enthusiast with a profound interest in understanding the intricacies of computer programming. My skills are not limited to application programming in Java; I have also delved deeply into computer hardware, learning about various architectures, low-level assembly programming, Linux kernel implementation, and writing device drivers. The contributions of Linus Torvalds, Ken Thompson, and Dennis Ritchie—who revolutionized the computer industry—inspire me. I believe that real contributions to computer science are made by mastering all levels of abstraction and understanding systems inside out.

In addition to my professional pursuits, I am passionate about teaching and sharing knowledge. I have spent two years as a teaching assistant at UW Madison, where I taught complex concepts in operating systems, computer graphics, and data structures to both graduate and undergraduate students. Currently, I am an assistant professor at KIIT, Bhubaneswar, where I continue to teach computer science to undergraduate and graduate students. I am also working on writing a few free books on systems programming, as I believe in freely sharing knowledge to empower others.

Comments

Join the discussion

No comments yet. Be the first to comment.

C Programming

Part 23 of 50

Up next

Pros use Conditional Compilation

Let's explore conditional compilation in C with detailed examples, including the use of #ifdef, #ifndef, #else, #endif, and #undef. We'll also incorporate bash scripting and environment variables to demonstrate dynamic control over compilation. Examp...

More from this blog

Why Energy and Momentum Are Conserved: Noether's Theorem, Derived by Hand

Two conservation laws, derived from scratch with first-year calculus, then measured to check.

Aug 10, 202630 min read

Socket Programming in Java: Understanding TCP Communication

Socket programming forms the backbone of network communication in modern applications. Whether you're building a web service, a chat application, or a distributed system, understanding how to work wit

Aug 6, 202626 min read

Computer Arithmetic: From Fast Adders to Floating-Point

Arithmetic is the beating heart of every processor. Whether your machine is rendering 3-D graphics, training a neural network, or simply incrementing a loop counter, the ALU (Arithmetic Logic Unit) is doing the heavy lifting. In this deep-dive, I wan...

Feb 12, 202629 min read

The Complete Memory Hierarchy: From Semiconductor RAM to Virtual Memory

The performance gap between processors and main memory has been widening for decades. Modern processors can execute billions of instructions per second, but accessing data from main memory takes hundreds of processor cycles. This disparity creates a ...

Jan 7, 202670 min read

The Ultimate Spring Boot Guide: From Fundamentals to Production-Ready REST APIs

Introduction Welcome to the most comprehensive Spring Boot guide you'll find! This isn't just another tutorial that skims the surface. We're going to dive deep into every concept, explain every annotation, walk through every line of code, and underst...

Dec 26, 2025125 min read

Jyotiprakash's Blog

253 posts

I'm Jyotiprakash, a software dev and professor at KIIT, with expertise in system programming.

The #include directive is used in C programming to include the contents of a header file into the source code during the compilation process. This is a fundamental mechanism for organizing code into modular components and reusing code across multiple source files. Let's take a detailed look at the #include directive with a larger example:

Suppose we have three files:

main.c: The main source file where the program starts.

 // main.c

 #include <stdio.h>
 #include "math_operations.h" // Include our custom header file

 int main() {
     int a = 10, b = 5;

     printf("Sum: %d\n", add(a, b));
     printf("Difference: %d\n", subtract(a, b));

     return 0;
 }

math_operations.h: A custom header file that declares functions for mathematical operations.

 // math_operations.h

 #ifndef MATH_OPERATIONS_H
 #define MATH_OPERATIONS_H

 int add(int a, int b);
 int subtract(int a, int b);

 #endif // MATH_OPERATIONS_H

math_operations.c: The implementation of the functions declared in math_operations.h.

 // math_operations.c

 #include "math_operations.h"

 int add(int a, int b) {
     return a + b;
 }

 int subtract(int a, int b) {
     return a - b;
 }

Now, let's break down how the #include directive works in this example:

main.c:
- The #include <stdio.h> includes the standard input/output library, which provides functions like printf.
- The #include "math_operations.h" includes the custom header file math_operations.h. This allows the main.c file to use the functions declared in math_operations.h without needing to know their implementations.
math_operations.h:
- The #ifndef, #define, and #endif lines are used for header guards. They prevent the header file from being included multiple times in the same compilation unit, which helps avoid redefinition errors.
- The file declares two functions add and subtract without providing their implementations. This is the interface that other files can use.
math_operations.c:
- The #include "math_operations.h" line includes the same header file that was included in main.c. This ensures that the function declarations in math_operations.h match the actual implementations in this file.
- The file provides the implementations for the add and subtract functions.

When you compile the program, you typically compile all source files together. For example:

gcc main.c math_operations.c -o my_program

This compilation command tells the compiler to compile both main.c and math_operations.c together, linking them into the executable my_program. The #include directives facilitate the organization of code into separate files and enable code reuse, making the program more modular and maintainable.

Command Palette

Comments

C Programming

Pros use Conditional Compilation

More from this blog