ft_printf – Recreating printf in C

This is my implementation of ft_printf, a foundational project at 42 where we re-create the functionality of the standard printf function in C. This project gave me hands-on experience with variadic functions, manual type conversion, and output formatting, while reinforcing modular programming practices in low-level C.

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🚀 Project Overview

The goal of this project was to write a simplified version of the standard printf function from scratch. This includes:

• Parsing a format string
• Handling a variable number of arguments
• Converting different data types to formatted output
• Writing each output character manually

This library compiles into a static library libftprintf.a, which can be reused in future C projects.

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🧠 What I Learned

• How variadic functions work using stdarg.h
• How to convert integers, hexadecimals, and pointers to strings manually
• Structuring reusable and testable code in C
• Writing helper functions for string and character output
• Implementing custom formatting logic without relying on standard C library I/O functions like printf
• Managing memory carefully and avoiding leaks
• Writing and maintaining a proper Makefile
• Combining ft_printf with my custom libft for extended functionality

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📁 Project Structure

ft_printf/
├── ft_printf.c          # Main printf logic and format parser
├── ft_printf.h          # Header file with declarations and macros
├── ft_putchar_pf.c      # Writes a single character
├── ft_putstr_pf.c       # Writes a string
├── ft_putnbr_pf.c       # Converts and prints signed integers
├── ft_putuint_pf.c      # Converts and prints unsigned integers
├── ft_puthex_pf.c       # Converts and prints hex numbers
├── ft_putptr_pf.c       # Converts and prints pointers (with "0x" prefix)
├── Makefile             # Build rules for compiling the static library
└── libft/               # My custom implementation of C standard library functions

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✅ Supported Format Specifiers

Specifier	Description
%c	Print a single character
%s	Print a string
%d / %i	Print a signed decimal integer
%u	Print an unsigned decimal integer
%x	Print an unsigned hexadecimal (lowercase)
%X	Print an unsigned hexadecimal (uppercase)
%p	Print a pointer (as hexadecimal with 0x prefix)
%%	Print a literal percent sign

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🧪 Test Your Implementation

You can test your libft implementation using Francinette, a popular automated testing tool designed for 42 libft projects.

To use Francinette:

1. Clone the repo:

   git clone https://github.com/alelievr/francinette.git

2. Follow the instructions in its README to set up and run tests.

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🛠️ How to Use

1. Clone the repository:

git clone https://github.com/your-username/ft_printf.git
cd ft_printf

2. Build the library:

make

This will compile all .c files and produce the static library libftprintf.a. It also builds libft as a dependency.

3. Include it in your own C program:

In your C file:

#include "ft_printf.h"

To compile:

 gcc -Wall -Wextra -Werror main.c libftprintf.a -I. -Ilibft 

🛠️ Example Usage:

#include "ft_printf.h"

int main(void)
{
    int score = 95;
    char *name = "Hossein";

    ft_printf("Hello, %s!\n", name);
    ft_printf("You scored %d%% on your test.\n", score);
    ft_printf("Memory address: %p\n", name);
    ft_printf("Hex value: %x | Upper: %X\n", 255, 255);

    return (0);
}

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🧾 License

This project is part of the 42 School curriculum. You’re welcome to use and learn from it, but do not copy it directly for your own submission.

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👤 Author

Hossein Khoshnevis
🧠 Software Developer | 📍 Based in the Netherlands
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