_printf

Custom implementation of the C printf function using variadic functions, format parsing and low-level output handling.

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Description

_printf is a custom implementation of the standard C library function printf.

This project reproduces basic formatted output behavior by parsing a format string and printing supported conversion specifiers to the standard output.

The project was developed as part of the Holberton School curriculum to practice variadic functions, modular programming, manual string parsing and low-level output handling in C.

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Objectives

• Recreate part of the behavior of the standard printf function.
• Understand variadic functions with va_list, va_start, va_arg and va_end.
• Parse format strings manually.
• Handle different conversion specifiers.
• Write output using low-level functions.
• Organize C code into modular functions.
• Practice memory-safe and readable C programming.

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Supported Format Specifiers

Specifier	Description
%c	Prints a single character
%s	Prints a string of characters
%d	Prints a signed decimal integer
%i	Prints a signed decimal integer
%%	Prints a literal percent character

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Technologies Used

• C
• GCC
• Linux / Ubuntu
• Variadic functions
• Git
• Betty style checker
• Valgrind

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Prerequisites

This project was developed and tested using:

• Ubuntu 20.04 LTS
• GCC
• Git
• Betty style checker
• Valgrind

Check GCC installation:

gcc --version

Check Valgrind installation:

valgrind --version

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Installation

Clone the repository:

git clone https://github.com/Alreix/holbertonschool-printf.git
cd holbertonschool-printf

Compile the project with a test file:

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

This creates an executable named:

_printf

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Usage

Create or use a main.c file to test the _printf function.

Example:

#include "main.h"

int main(void)
{
    _printf("Character: %c\n", 'H');
    _printf("String: %s\n", "Holberton");
    _printf("Integer: %d\n", 2026);
    _printf("Percent: %%\n");

    return (0);
}

Compile:

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

Run:

./_printf

Example output:

Character: H
String: Holberton
Integer: 2026
Percent: %

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Project Structure

holbertonschool-printf/
├── main.h                  # Header file with prototypes and structures
├── _printf.c               # Main _printf function
├── print_char.c            # Character printing handler
├── print_string.c          # String printing handler
├── print_integer.c         # Integer printing handler
├── get_function.c          # Specifier selection logic
├── man_3_printf            # Manual page
├── Images/                 # Images used in the README
└── README.md               # Project documentation

File names may vary depending on the final project organization.

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Features

• Custom _printf function.
• Format string parsing.
• Support for %c, %s, %d, %i and %%.
• Modular handler functions.
• Manual output handling.
• Return value based on number of printed characters.
• Manual page included.

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Screenshots

Example test file:

Example output:

Flowchart:

Manual page preview:

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Manual Page

A manual page is included in the repository.

To display it, use:

man ./man_3_printf

Or, depending on your environment:

man 3 _printf

Summary of sections

• NAME — brief description
• SYNOPSIS — basic usage
• DESCRIPTION — main features
• RETURN VALUE — descriptions of returned values
• EXAMPLES — usage examples
• ADDITIONAL INFORMATION — date, authors, and extra notes

For more details, please refer to the full man page below.

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Testing

A main.c file was used for testing.

Compile and run:

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

To ensure memory safety, use the following command:

valgrind --leak-check=full ./_printf

This will detect:

• memory leaks;
• invalid memory accesses;
• use of uninitialized memory.

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Flowchart

The flowchart below illustrates the main steps and logic of the project.

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Additional Notes

The project emphasizes modularity: each specifier is handled by a dedicated function.

Care must be taken with pointer handling.

Variadic functions such as va_list, va_start, va_arg, and va_end are crucial to the implementation.

The authors of this project are Morgane Abbattista (Alreix) and Nicolas Da Silva (NicolasDS83600).

The project was initialized on 11/24/2025 and completed on 11/27/2025.