ft_printf

A custom reimplementation of the printf function in C, built as part of 42's common core curriculum.

About

ft_printf recreates the core behavior of the standard C library's printf, handling variadic arguments and formatted output without relying on the original implementation. The goal is to understand how a formatted output function actually works under the hood: parsing a format string, handling variadic arguments with stdarg.h, and converting values to their correct string representation for each format specifier.

Supported conversions

Specifier	Description
%c	character
%s	string
%p	pointer address
%d	signed decimal integer
%i	signed decimal integer
%u	unsigned decimal integer
%x	unsigned hexadecimal integer (lowercase)
%X	unsigned hexadecimal integer (uppercase)
%%	literal percent sign

(Adjust this table if you implemented additional flags/specifiers, such as width, precision, or the -, 0, # flags.)

Build

ft_printf is meant to be compiled as a static library and linked into other projects.

make

This generates libftprintf.a at the root of the project.

Other available targets:

make clean    # removes object files
make fclean   # removes object files and the library
make re       # rebuilds the library from scratch

Usage

Include the header and link the library when compiling your project:

#include "ft_printf.h"

int main(void)
{
    ft_printf("Hello, %s! You are %d years old.\n", "world", 42);
    ft_printf("Pointer: %p, hex: %x\n", &main, 255);
    return (0);
}

cc -Wall -Wextra -Werror main.c -L. -lftprintf -o test
./test

Project structure

ft_printf/
├── srcs/
│   ├── ft_printf.c
│   ├── conversions/
│   └── utils/
├── includes/
│   └── ft_printf.h
├── libft/          # personal library reused across projects
├── Makefile
└── README.md

(Adjust this tree to match your actual project structure.)

What I learned

• Working with variadic functions using stdarg.h (va_start, va_arg, va_end)
• Converting values between types and formatting them correctly for each base and representation (decimal, hexadecimal, pointer addresses)
• Designing a small, extensible parser for a format string
• Building and linking a static library (.a) for reuse across other C projects

Authors

• Nathan Jeanbourquin — 42

License

Project built as part of the 42 curriculum. Educational use.