🖨️ ft_printf

A reimplementation of the standard C printf() function written from scratch, designed to demonstrate variadic functions, formatted output processing, and low-level memory handling.

ft_printf is one of the fundamental projects of the 42 curriculum, where the goal is to recreate the behavior of the standard printf function using only a limited subset of the C standard library.

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Quick Overview

• Built with: C
• Focus: Recreating printf-like output formatting, variadic functions, and format parsing.
• What I learned: Modular design, parsing logic, variadic arguments, type handling, and careful output management.

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📌 Project Objective

Recreate the function:

int ft_printf(const char *format, ...);

The function must:

• Parse a format string

• Detect format specifiers

• Retrieve variadic arguments

• Format and print the output correctly

• Return the number of printed characters

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⚙️ Supported Format Specifiers

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

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🧠 Core Concept — Variadic Functions

ft_printf relies on variadic arguments, allowing functions to accept a variable number of parameters.

Example:

int ft_printf(const char *format, ...);

Arguments are accessed using:

va_list args;
va_start(args, format);
va_arg(args, type);
va_end(args);

Flow:

ft_printf()
   │
   ▼
parse format string
   │
   ▼
detect %
   │
   ▼
retrieve argument
   │
   ▼
format output
   │
   ▼
write to stdout

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🔎 Parsing the Format String

The algorithm scans the string character by character.

Example:

ft_printf("Hello %s %d", name, age);

Parsing Steps

H → print
e → print
l → print
l → print
o → print
(space)
% → specifier detected
s → print string
(space)
% → specifier detected
d → print integer

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🧩 Conversion Handling

Each specifier triggers a dedicated conversion function.

Example architecture:

ft_printf
 │
 ├── handle_char
 ├── handle_string
 ├── handle_pointer
 ├── handle_integer
 ├── handle_unsigned
 ├── handle_hex
 └── handle_percent

Each handler:

• Retrieves the argument using va_arg

• Converts it to a printable format

• Writes it using write()

📊 Output Flow

FORMAT STRING
      │
      ▼
  ft_printf
      │
      ▼
FORMAT PARSER
      │
      ▼
SPECIFIER DETECTED
      │
      ▼
ARGUMENT RETRIEVAL
      │
      ▼
CONVERSION FUNCTION
      │
      ▼
write() → STDOUT

📁 Project Structure

ft_printf/
│
├── ft_printf.c
├── ft_printf.h
│
├── ft_putchar.c
├── ft_putstr.c
├── ft_putnbr.c
│
├── ft_puthex.c
├── ft_putptr.c
│
└── README.md

Core Files	File Role
ft_printf.c	Main formatting engine
ft_printf.h	Function prototypes
ft_putchar.c	Character printing
ft_putstr.c	String printing
ft_putnbr.c	Integer printing
ft_puthex.c	Hexadecimal conversion
ft_putptr.c	Pointer printing

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▶️ Example Usage

#include "ft_printf.h"

int main(void)
{
    ft_printf("Hello %s\n", "world");
    ft_printf("Number: %d\n", 42);
    ft_printf("Hex: %x\n", 255);
    ft_printf("Pointer: %p\n", &main);
}

📄 Example Output

Hello world
Number: 42
Hex: ff
Pointer: 0x7ffee4b6c9a0

⚡ Compilation

Compile using:

cc -Wall -Wextra -Werror *.c

Or with a Makefile:

make

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🧩 Challenges Solved

• Implementing printf from scratch requires solving several non-trivial problems:

• Parsing formatted strings

• Handling variadic arguments

• Implementing number-to-string conversions

• Managing hexadecimal and pointer formatting

• Handling edge cases

• Returning accurate printed length

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🛠 Skills Developed

• Low-Level Programming

• variadic functions

• formatted output

• system calls (write)

• Memory Handling

• stack argument management

• integer conversion algorithms

• Algorithm Design

• parsing engines

• format interpretation

• Debugging

• segmentation faults

• incorrect format parsing

• integer conversion bugs

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📚 Concepts Mastered

• variadic functions (stdarg.h)

• formatted string parsing

• integer-to-string conversion

• hexadecimal representation

• pointer formatting

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👨‍💻 Author

Walid Krati

Software Engineering Student • System Programming • C

GitHub:

https://github.com/wkratos77

⭐ If you found this project interesting, feel free to explore the implementation.