This project has been created as part of the 42 curriculum by lmatthes.

libft

Description

libft is a static C library (libft.a) that reimplements a selection of standard C library functions and adds a set of extra utilities that are useful across the 42 curriculum. It is the first project of the cursus and provides a reusable toolbox of functions that later projects can link against.

The library is organised in three parts:

1. libc functions — reimplementations of common <string.h>, <ctype.h> and <stdlib.h> functions, prefixed with ft_ (for example strlen becomes ft_strlen). Each follows the expected behaviour of the original function.
2. Additional functions — string and output helpers that are not part of the standard C library, or that exist in a different form (ft_substr, ft_split, ft_itoa, the ft_put*_fd family, and others).
3. Linked list — functions to create and manipulate a simple singly linked list built on the t_list structure.

No global variables are used, helper functions are kept static within their files, and every function is written to comply with the 42 Norm.

Instructions

The project ships with a Makefile. From the repository root:

make        # build libft.a
make clean  # remove object files
make fclean # remove object files and libft.a
make re     # rebuild from scratch

Sources compile with cc -Wall -Wextra -Werror, and the archive is produced with ar.

To use the library in your own program, include the header and link the archive:

#include "libft.h"

cc main.c -L. -lft -o my_program
# or, linking the archive directly:
cc main.c libft.a -o my_program

Library contents

Part 1 — libc functions

• Character classification: ft_isalpha, ft_isdigit, ft_isalnum, ft_isascii, ft_isprint
• Case conversion: ft_toupper, ft_tolower
• Memory: ft_memset, ft_bzero, ft_memcpy, ft_memmove, ft_memchr, ft_memcmp
• Strings: ft_strlen, ft_strlcpy, ft_strlcat, ft_strchr, ft_strrchr, ft_strncmp, ft_strnstr
• Conversion: ft_atoi
• Allocation: ft_calloc, ft_strdup

Part 2 — Additional functions

• ft_substr, ft_strjoin, ft_strtrim, ft_split, ft_itoa, ft_strmapi, ft_striteri
• Output to a file descriptor: ft_putchar_fd, ft_putstr_fd, ft_putendl_fd, ft_putnbr_fd

Part 3 — Linked list

The t_list node stores a void *content and a pointer to the next node.

• ft_lstnew, ft_lstadd_front, ft_lstsize, ft_lstlast, ft_lstadd_back, ft_lstdelone, ft_lstclear, ft_lstiter, ft_lstmap

Resources

• The man pages for each reimplemented function (for example man strlen, man memmove, man strlcat).
• The C Programming Language (Kernighan & Ritchie) for language fundamentals.
• The 42 Norm document for the coding standard enforced by norminette.

Use of AI

AI was used as a support tool during this project for reviewing ideas, clarifying concepts, and improving documentation. It was not used as a replacement for understanding the implementation.

All functions were reviewed, tested, and validated with norminette, behaviour checks against the system C library where applicable, and memory checks using AddressSanitizer and malloc fault-injection for allocating functions.