This project has been created as part of the 42 curriculum by vneves-c.

libft

A C library of general-purpose functions, built from scratch as the first project of the 42 Common Core.

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Description

libft is a custom C standard library written without relying on any libc functions. The goal is to deeply understand how foundational C functions work by reimplementing them — covering memory manipulation, string handling, character classification, linked lists, and output utilities.

This library is designed to be reused across all future 42 projects, making it a long-term tool rather than a one-off exercise.

The project is divided into three parts:

• Part 1 — Reimplementations of standard libc functions (ft_strlen, ft_memcpy, ft_strchr, etc.)
• Part 2 — Additional utility functions not found in libc (ft_split, ft_itoa, ft_substr, etc.)
• Part 3 — Linked list manipulation functions using the t_list structure

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Instructions

Compilation

Clone the repository and run make at the root:

git clone https://github.com/viniciusnevescosta/Libft.git
cd Libft
make

This produces libft.a at the root of the directory.

Cleaning

make clean    # removes object files
make fclean   # removes object files and libft.a
make re       # fclean + full rebuild

Using in a project

Include the header and link the archive at compile time:

#include "libft.h"

cc -Wall -Wextra -Werror main.c -L. -lft -o program

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Library Reference

Part 1 — Libc Functions

Function	Description
ft_isalpha	Returns 1 if c is an alphabetic character, 0 otherwise
ft_isdigit	Returns 1 if c is a decimal digit character, 0 otherwise
ft_isalnum	Returns 1 if c is alphanumeric, 0 otherwise
ft_isascii	Returns 1 if c is a 7-bit ASCII character, 0 otherwise
ft_isprint	Returns 1 if c is a printable character, 0 otherwise
ft_strlen	Returns the length of a null-terminated string
ft_memset	Fills n bytes of memory starting at b with value c
ft_bzero	Sets n bytes of memory at s to zero
ft_memcpy	Copies n bytes from src to dst (no overlap)
ft_memmove	Copies n bytes from src to dst, handling overlap safely
ft_strlcpy	Copies up to dstsize - 1 chars from src to dst, null-terminates; returns strlen(src)
ft_strlcat	Appends src to dst up to dstsize total; returns combined length
ft_toupper	Returns the uppercase equivalent of c, or c unchanged
ft_tolower	Returns the lowercase equivalent of c, or c unchanged
ft_strchr	Returns a pointer to the first occurrence of c in s, or NULL
ft_strrchr	Returns a pointer to the last occurrence of c in s, or NULL
ft_strncmp	Compares up to n characters of s1 and s2; returns the difference
ft_memchr	Searches the first n bytes of s for byte c; returns pointer or NULL
ft_memcmp	Compares n bytes of s1 and s2; returns the difference
ft_strnstr	Finds needle in haystack, searching at most len characters
ft_atoi	Converts the initial portion of str to an int
ft_calloc	Allocates count * size zero-initialized bytes; returns pointer or NULL
ft_strdup	Returns a malloc'd copy of string s1, or NULL on failure

Part 2 — Additional Functions

Function	Description
ft_substr	Allocates and returns a substring of s starting at start with max length len
ft_strjoin	Allocates and returns the concatenation of s1 and s2
ft_strtrim	Allocates a copy of s1 with characters in set removed from both ends
ft_split	Splits s on delimiter c; returns a NULL-terminated array of strings
ft_itoa	Converts integer n to a malloc'd string representation
ft_strmapi	Applies function f(index, char) to each character of s; returns new string
ft_striteri	Applies function f(index, &char) to each character of s in place
ft_putchar_fd	Writes character c to file descriptor fd
ft_putstr_fd	Writes string s to file descriptor fd
ft_putendl_fd	Writes string s followed by a newline to file descriptor fd
ft_putnbr_fd	Writes integer n to file descriptor fd

Part 3 — Linked List

The list is built on the following structure, defined in libft.h:

typedef struct s_list
{
    void            *content;
    struct s_list   *next;
}   t_list;

Function	Description
ft_lstnew	Allocates and returns a new node with content; next set to NULL
ft_lstadd_front	Inserts node new at the beginning of list *lst
ft_lstsize	Returns the number of nodes in the list
ft_lstlast	Returns a pointer to the last node of the list
ft_lstadd_back	Appends node new to the end of list *lst
ft_lstdelone	Frees the content of node lst using del, then frees the node
ft_lstclear	Frees all nodes in the list using del; sets the pointer to NULL
ft_lstiter	Applies function f to the content of each node
ft_lstmap	Creates a new list by applying f to each node's content; uses del on failure

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Resources

References

• 42 Norm v4.1 — coding standard applied throughout
• norminette — automated norm checker

AI Usage

Claude and Gemini was used as a learning aid throughout the project, in two ways:

1. Clarifying concepts — when in doubt about how a specific function was supposed to behave (edge cases, return values, memory semantics), questions were asked to the AI to understand the underlying behavior before writing any code.

2. Code review — after writing each function independently, the AI was asked to evaluate the implementation and point out logical errors, undefined behavior, or norm violations. All fixes were applied and understood before moving on.