Practical Guide – Building and Using a Static Library (Single Folder Setup)

UpdatedMarch 25, 2026

Heya! 👋 I love helping people, and one of the best ways I do this is by sharing my knowledge and experiences. My journey reflects the power of growth and transformation, and I’m here to document and share it with you.

I started as a pharmacist, practicing at a tertiary hospital in the Northern Region of Ghana. There, I saw firsthand the challenges in healthcare delivery and became fascinated by how technology could offer solutions. This sparked my interest in digital health, a field I believe holds the key to revolutionizing healthcare.

Determined to contribute, I taught myself programming, mastering tools like HTML, CSS, JavaScript, React, PHP, and more. But I craved deeper knowledge and practical experience. That’s when I joined the ALX Software Engineering program, which became a turning point. Spending over 70 hours a week learning, coding, and collaborating, I transitioned fully into tech.

Today, I am a Software Engineer and Digital Health Solutions Architect, building and contributing to innovative digital health solutions. I combine my healthcare expertise with technical skills to create impactful tools that solve real-world problems in health delivery.

Imposter syndrome has been part of my journey, but I’ve learned to embrace it as a sign of growth. Livestreaming my learning process, receiving feedback, and building in public have been crucial in overcoming self-doubt. Each experience has strengthened my belief in showing up, staying consistent, and growing through challenges.

Through this platform, I document my lessons, challenges, and successes to inspire and guide others—whether you’re transitioning careers, exploring digital health, or diving into software development.

I believe in accountability and the value of shared growth. Your feedback keeps me grounded and motivated to continue this journey. Let’s connect, learn, and grow together! 🚀

Comments

Join the discussion

No comments yet. Be the first to comment.

C Programming

Part 34 of 40

From today, I will be starting lessons on C programming in my ALX Software Engineering class and I look forward to sharing with you everything I learn through this series.

Up next

How Programs Receive Input (argc & argv Basics)

Up to this point, most of your C programs have looked like this: int x = 5; You hardcode values directly inside the program. That works… but it’s limited. What if you want your program to behave diff

🟦 Scenario

You have multiple functions you’ve written before, like:

_strlen
_puts
_isalpha
_isdigit

Instead of copying them into every program, you want to:

Combine them into a reusable static library and use them in another program.

🟩 Step 1: Your Starting Files (All in One Folder)

Your directory looks like this:

0-strlen.c
1-puts.c
2-isalpha.c
3-isdigit.c
_putchar.c
main.h
main.c

🔹 What each file does:

.c files → your function implementations
main.h → function prototypes
main.c → program that will use the library

🟩 Step 2: Write Your Header File (`main.h`)

#ifndef MAIN_H
#define MAIN_H

int _strlen(char *s);
void _puts(char *s);
int _isalpha(int c);
int _isdigit(int c);
int _putchar(char c);

#endif

👉 This file tells the compiler what functions exist.

🟩 Step 3: Compile All `.c` Files into `.o` Files

Run:

gcc -Wall -Werror -Wextra -pedantic -std=gnu89 -c *.c

⚠️ Important Note

This will also compile main.c into main.o.

That’s fine — we just won’t include it in the library.

After this step, you get:

0-strlen.o
1-puts.o
2-isalpha.o
3-isdigit.o
_putchar.o
main.o

🟩 Step 4: Create the Static Library

Now we bundle ONLY the function object files (not main.o).

ar -rc libmy.a 0-strlen.o 1-puts.o 2-isalpha.o 3-isdigit.o _putchar.o

Now you have:

libmy.a

👉 This is your static library.

🟩 Step 5: Index the Library

ranlib libmy.a

👉 This allows the compiler to find functions inside the library quickly.

🟩 Step 6: Check What’s Inside the Library (Optional)

ar -t libmy.a

You should see:

0-strlen.o
1-puts.o
2-isalpha.o
3-isdigit.o
_putchar.o

🟩 Step 7: Write a Program That Uses the Library

main.c

#include "main.h"

int main(void)
{
    _puts("Hello from my static library!");
    return 0;
}

🟩 Step 8: Compile and Link the Library

Now the most important command:

gcc main.c -L. -lmy -o myprogram

🔍 Breakdown

Part	Meaning
`main.c`	your program
`-L.`	look for libraries in current directory
`-lmy`	link `libmy.a`
`-o myprogram`	output executable

🔑 Key Rule

libmy.a → -lmy

Remove:

lib
.a

🟩 Step 9: Run Your Program

./myprogram

Output:

Hello from my static library!

🟦 What Just Happened (Behind the Scenes)

When you ran:

gcc main.c -L. -lmy

The compiler:

Saw _puts() in your code
Looked inside libmy.a
Found _puts
Copied its compiled code into your program

👉 Only the functions you use are included.

🟦 Important Insight

Even if your library contains:

50 functions

Your program might only include:

1 function

This keeps your executable efficient.

🟦 Clean Up (Optional but Recommended)

Remove .o files after building the library:

rm *.o

Your folder becomes:

0-strlen.c
1-puts.c
2-isalpha.c
3-isdigit.c
_putchar.c
main.h
main.c
libmy.a
myprogram

Clean and organized.

🟦 Common Mistakes (Very Important)

❌ Forgetting `-L.`

library not found

👉 Fix:

-L.

❌ Wrong library name

-lmy   ✅ correct
-llibmy ❌ wrong

❌ Forgetting `ranlib`

Sometimes causes linking issues.

Always run:

ranlib libmy.a

❌ Including `main.o` in library

👉 Never include your main program in the library.

🟦 Practice (Without Solving Project Directly)

Try this:

Add 2–3 more functions to your .c files
Rebuild your library
Write a program that uses only ONE of those functions
Compile and run

👉 Observe: only the used function is included.

🟦 Final Mental Model

Think of it like this:

Functions → compiled → packaged → linked → executable

🟦 Key Takeaways

Static libraries bundle compiled functions into one file
You compile .c → .o → .a
You link using:

gcc main.c -L. -lmy -o program

Only used functions are included
Your final program becomes self-contained

What’s Next

Now that you understand the full workflow, you are ready to:

Build your own static library for the project
Organize your functions properly
Follow the required rules

This is one of the most important steps toward writing modular and reusable C code.

Practical Guide – Building and Using a Static Library (Single Folder Setup)

Comments

C Programming

How Programs Receive Input (argc & argv Basics)

More from this blog

Choosing the Right AI Model for the Job

How Source Documents Make AI More Reliable

Why AI Sounds Smart Even When It Is Wrong

Prompt Engineering: Thinking Like a Professional AI User

How AI actually processes your prompt under the hood

🟦 Scenario

🟩 Step 1: Your Starting Files (All in One Folder)

🔹 What each file does:

🟩 Step 2: Write Your Header File (`main.h`)

🟩 Step 3: Compile All `.c` Files into `.o` Files

⚠️ Important Note

After this step, you get:

🟩 Step 4: Create the Static Library

Now you have:

🟩 Step 5: Index the Library

🟩 Step 6: Check What’s Inside the Library (Optional)

🟩 Step 7: Write a Program That Uses the Library

🟩 Step 8: Compile and Link the Library

🔍 Breakdown

🔑 Key Rule

🟩 Step 9: Run Your Program

🟦 What Just Happened (Behind the Scenes)

🟦 Important Insight

🟦 Clean Up (Optional but Recommended)

🟦 Common Mistakes (Very Important)

❌ Forgetting `-L.`

❌ Wrong library name

❌ Forgetting `ranlib`

❌ Including `main.o` in library

🟦 Practice (Without Solving Project Directly)

🟦 Final Mental Model

🟦 Key Takeaways

What’s Next

Command Palette

Comments

C Programming

How Programs Receive Input (argc & argv Basics)

More from this blog

🟦 Scenario

🟩 Step 1: Your Starting Files (All in One Folder)

🔹 What each file does:

🟩 Step 2: Write Your Header File (main.h)

🟩 Step 3: Compile All .c Files into .o Files

⚠️ Important Note

After this step, you get:

🟩 Step 4: Create the Static Library

Now you have:

🟩 Step 5: Index the Library

🟩 Step 6: Check What’s Inside the Library (Optional)

🟩 Step 7: Write a Program That Uses the Library

🟩 Step 8: Compile and Link the Library

🔍 Breakdown

🔑 Key Rule

🟩 Step 9: Run Your Program

🟦 What Just Happened (Behind the Scenes)

🟦 Important Insight

🟦 Clean Up (Optional but Recommended)

🟦 Common Mistakes (Very Important)

❌ Forgetting -L.

❌ Wrong library name

❌ Forgetting ranlib

❌ Including main.o in library

🟦 Practice (Without Solving Project Directly)

🟦 Final Mental Model

🟦 Key Takeaways

What’s Next

🟩 Step 2: Write Your Header File (`main.h`)

🟩 Step 3: Compile All `.c` Files into `.o` Files

❌ Forgetting `-L.`

❌ Forgetting `ranlib`

❌ Including `main.o` in library