libft

A complete reimplementation of the C standard library — from scratch, without using any of the original functions.

🇧🇷 Leia em Português

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Why this project matters

"This project taught me how the C standard library actually works under the hood — how strings are traversed byte by byte, how memory is allocated and manipulated manually, and what it truly means to write reliable, reusable code."

Understanding these fundamentals is what separates a developer who uses tools from one who understands them. Every senior engineer working in systems programming, embedded, or performance-critical environments thinks at this level of abstraction.

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What was built

A fully functional personal C library (libft.a) covering:

Memory

Function	Description
ft_memset	Fill memory with a byte value
ft_bzero	Zero out a memory area
ft_memcpy	Copy memory areas
ft_memmove	Safe memory copy with overlap handling
ft_memchr	Locate byte in memory
ft_memcmp	Compare memory areas
ft_calloc	Allocate and zero-initialize memory

Strings

Function	Description
ft_strlen	String length
ft_strdup	Duplicate a string
ft_strchr / ft_strrchr	Character search
ft_strncmp	String comparison
ft_strlcpy / ft_strlcat	Safe string copy and concat
ft_strnstr	Substring search
ft_substr	Extract substring
ft_strjoin	Join two strings
ft_strtrim	Trim characters from edges
ft_split	Split string by delimiter
ft_strmapi / ft_striteri	Functional map over string

Conversion

Function	Description
ft_atoi	String to integer
ft_itoa	Integer to string
ft_toupper / ft_tolower	Character case conversion

Output

Function	Description
ft_putchar_fd	Write char to file descriptor
ft_putstr_fd	Write string to file descriptor
ft_putendl_fd	Write string + newline
ft_putnbr_fd	Write integer

Linked Lists (Bonus)

Function	Description
ft_lstnew	Create new node
ft_lstadd_front / ft_lstadd_back	Add node to front/back
ft_lstsize	Count list nodes
ft_lstlast	Get last node
ft_lstdelone / ft_lstclear	Delete node(s)

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A standout technical detail

The implementation of ft_split correctly handles edge cases such as consecutive delimiters, leading/trailing delimiters, and empty strings — situations where many naive implementations silently fail or leak memory. This demonstrates careful thinking about boundary conditions, not just the happy path.

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Getting Started

git clone https://github.com/gustavofsousa/libft-42.git
cd libft-42
make

This produces libft.a. To use it in your project:

#include "libft.h"

Compile with:

gcc your_file.c -L. -lft -o your_program

Available make targets

Target	Action
make	Build the library
make bonus	Build with linked list functions
make clean	Remove object files
make fclean	Remove object files and library
make re	Full rebuild

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Skills demonstrated

• Manual memory management in C
• Pointer arithmetic and string manipulation
• Makefile and static library creation (ar)
• Defensive programming and edge case handling
• Linked list data structure implementation

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License

This project was developed as part of the 42 School curriculum.

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Made with ☕ at 42 Rio de Janeiro