Libft

Rebuilding the C standard library from scratch — one function at a time.

📖 About

Libft is the first project of the 42 School curriculum. The goal is to re-implement a set of standard C library functions, as well as some additional utility functions that will be reused throughout the entire 42 cursus.

This project is about truly understanding how fundamental C functions work under the hood — memory manipulation, string handling, linked lists, and more — by writing every single one yourself.

---

---

⚙️ Functions

Part 1 — Libc Functions

Re-implementations of standard C library functions, prefixed with ft_.

Function	Prototype	Description
ft_isalpha	int ft_isalpha(int c)	Check if character is alphabetic
ft_isdigit	int ft_isdigit(int c)	Check if character is a digit
ft_isalnum	int ft_isalnum(int c)	Check if character is alphanumeric
ft_isascii	int ft_isascii(int c)	Check if character is ASCII
ft_isprint	int ft_isprint(int c)	Check if character is printable
ft_strlen	size_t ft_strlen(const char *s)	Compute the length of a string
ft_memset	void *ft_memset(void *b, int c, size_t len)	Fill memory with a constant byte
ft_bzero	void ft_bzero(void *s, size_t n)	Zero out a memory block
ft_memcpy	void *ft_memcpy(void *dst, const void *src, size_t n)	Copy a memory area
ft_memmove	void *ft_memmove(void *dst, const void *src, size_t len)	Copy memory area (overlap-safe)
ft_strlcpy	size_t ft_strlcpy(char *dst, const char *src, size_t size)	Size-bounded string copy
ft_strlcat	size_t ft_strlcat(char *dst, const char *src, size_t size)	Size-bounded string concatenation
ft_toupper	int ft_toupper(int c)	Convert char to uppercase
ft_tolower	int ft_tolower(int c)	Convert char to lowercase
ft_strchr	char *ft_strchr(const char *s, int c)	Locate character in string
ft_strrchr	char *ft_strrchr(const char *s, int c)	Locate character in string (reverse)
ft_strncmp	int ft_strncmp(const char *s1, const char *s2, size_t n)	Compare two strings (n bytes)
ft_memchr	void *ft_memchr(const void *s, int c, size_t n)	Scan memory for a character
ft_memcmp	int ft_memcmp(const void *s1, const void *s2, size_t n)	Compare memory areas
ft_strnstr	char *ft_strnstr(const char *h, const char *n, size_t len)	Locate substring in string
ft_atoi	int ft_atoi(const char *str)	Convert string to integer
ft_calloc	void *ft_calloc(size_t count, size_t size)	Allocate zeroed memory
ft_strdup	char *ft_strdup(const char *s1)	Duplicate a string

---

Part 2 — Additional Functions

Custom utility functions built on top of libc.

Function	Prototype	Description
ft_substr	char *ft_substr(char const *s, unsigned int start, size_t len)	Extract a substring
ft_strjoin	char *ft_strjoin(char const *s1, char const *s2)	Concatenate two strings
ft_strtrim	char *ft_strtrim(char const *s1, char const *set)	Trim characters from both ends
ft_split	char **ft_split(char const *s, char c)	Split string by delimiter
ft_itoa	char *ft_itoa(int n)	Convert integer to string
ft_strmapi	char *ft_strmapi(char const *s, char (*f)(unsigned int, char))	Apply function to each char
ft_striteri	void ft_striteri(char *s, void (*f)(unsigned int, char *))	Apply function to each char (in place)
ft_putchar_fd	void ft_putchar_fd(char c, int fd)	Output a char to a file descriptor
ft_putstr_fd	void ft_putstr_fd(char *s, int fd)	Output a string to a file descriptor
ft_putendl_fd	void ft_putendl_fd(char *s, int fd)	Output a string + newline to fd
ft_putnbr_fd	void ft_putnbr_fd(int n, int fd)	Output an integer to a file descriptor

---

Bonus — Linked List Functions

Function	Prototype	Description
ft_lstnew	t_list *ft_lstnew(void *content)	Create a new list node
ft_lstadd_front	void ft_lstadd_front(t_list **lst, t_list *new)	Add node at the front
ft_lstsize	int ft_lstsize(t_list *lst)	Count nodes in a list
ft_lstlast	t_list *ft_lstlast(t_list *lst)	Return the last node
ft_lstadd_back	void ft_lstadd_back(t_list **lst, t_list *new)	Add node at the back
ft_lstdelone	void ft_lstdelone(t_list *lst, void (*del)(void *))	Delete a single node
ft_lstclear	void ft_lstclear(t_list **lst, void (*del)(void *))	Delete and free entire list
ft_lstiter	void ft_lstiter(t_list *lst, void (*f)(void *))	Iterate over a list
ft_lstmap	t_list *ft_lstmap(t_list *lst, void *(*f)(void *), void (*del)(void *))	Map a function over a list

---

🛠️ Usage

Clone the repository

git clone git@github.com:wangunuxe/Libft.git cd libft

Compile the library

make # builds libft.a make bonus # includes linked list functions make clean # removes object files make fclean # removes object files + libft.a make re # fclean + make

Use it in your project

gcc main.c -L. -lft -I. -o my_program

Testing

You can test your library with community testers:

Francinette — the most popular 42 tester