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

Libft

Description

libft is a custom C library built from scratch as part of the 42 curriculum. It reimplements essential functions from the standard C library including memory manipulation, string handling, character checks, and linked list operations without relying on external dependencies.

This project serves as a deep dive into low-level programming fundamentals and will be used as the foundation for other 42 projects in the future.

This version of libft includes ft_printf and get_next_line modules after completing them as part of the 42 curriculum.

Features

Libc functions

Function	Description
int ft_isalpha(int c);	Checks if a character is alphabetic (A-Z or a-z). Returns nonzero if true.
int ft_isdigit(int c);	Checks if a character is a decimal digit (0-9).
int ft_isalnum(int c);	Checks if a character is alphanumeric (letter or digit).
int ft_isascii(int c);	Checks if a character is within the ASCII range (0–127).
int ft_isprint(int c);	Checks if a character is printable (including space).
size_t ft_strlen(const char *s);	Returns the length of a string (excluding the null terminator).
void *ft_memset(void *s, int c, size_t n);	Fills a block of memory with a byte value.
void ft_bzero(void *s, size_t n);	Sets a block of memory to zero.
void *ft_memcpy(void *dest, const void *src, size_t n);	Copies n bytes from source to destination (no overlap handling).
void *ft_memmove(void *dest, const void *src, size_t n);	Copies n bytes safely, handling overlapping memory regions.
size_t ft_strlcpy(char *dst, const char *src, size_t size);	Copies a string into a buffer with size limit, always null‑terminating if size > 0.
size_t ft_strlcat(char *dst, const char *src, size_t size);	Appends a string to a buffer with size limit, ensuring null termination.
int ft_toupper(int c);	Converts a lowercase letter to uppercase.
int ft_tolower(int c);	Converts an uppercase letter to lowercase.
char *ft_strchr(const char *s, int c);	Finds the first occurrence of a character in a string.
char *ft_strrchr(const char *s, int c);	Finds the last occurrence of a character in a string.
int ft_strncmp(const char *s1, const char *s2, size_t n);	Compares two strings up to n characters.
void *ft_memchr(const void *s, int c, size_t n);	Searches for a byte value in memory.
int ft_memcmp(const void *s1, const void *s2, size_t n);	Compares two memory blocks.
char *ft_strnstr(const char *big, const char *little, size_t len);	Locates a substring within a string, searching up to len characters.
int ft_atoi(const char *nptr);	Converts a string to an integer.
void *ft_calloc(size_t nmemb, size_t size);	Allocates memory for an array and initialises it to zero.
char *ft_strdup(const char *s);	Duplicates a string by allocating new memory and copying its contents.

Additional functions

Function	Description
char *ft_substr(char const *s, unsigned int start, size_t len);	Allocates and returns a substring from string s, starting at index start and of maximum length len.
char *ft_strjoin(char const *s1, char const *s2);	Allocates and returns a new string that is the concatenation of s1 and s2.
char *ft_strtrim(char const *s1, char const *set);	Allocates and returns a copy of s1 with characters from set removed from the beginning and end.
char **ft_split(char const *s, char c);	Splits string s into an array of strings using character c as the delimiter.
char *ft_itoa(int n);	Converts an integer n into a string representation.
char *ft_strmapi(char const *s, char (*f)(unsigned int, char));	Applies function f to each character of string s, creating a new string with the results.
void ft_striteri(char *s, void (*f)(unsigned int, char*));	Applies function f to each character of string s, modifying the string in place.
void ft_putchar_fd(char c, int fd);	Writes character c to the given file descriptor fd.
void ft_putstr_fd(char *s, int fd);	Writes string s to the given file descriptor fd.
void ft_putendl_fd(char *s, int fd);	Writes string s followed by a newline to the given file descriptor fd.
void ft_putnbr_fd(int n, int fd);	Writes integer n as a string to the given file descriptor fd.

Linked list functions

Function	Description
t_list *ft_lstnew(void *content);	Allocates and returns a new list node, with its content initialized to the given value and next set to NULL.
void ft_lstadd_front(t_list **lst, t_list *new);	Adds the node new at the beginning of the list lst.
int ft_lstsize(t_list *lst);	Counts and returns the number of nodes in the list.
t_list *ft_lstlast(t_list *lst);	Returns the last node of the list.
void ft_lstadd_back(t_list **lst, t_list *new);	Adds the node new at the end of the list lst.
void ft_lstdelone(t_list *lst, void (*del)(void *));	Frees the memory of a single node’s content using del, then frees the node itself.
void ft_lstclear(t_list **lst, void (*del)(void *));	Deletes and frees all nodes of the list using del, leaving lst as NULL.
void ft_lstiter(t_list *lst, void (*f)(void *));	Iterates over the list and applies function f to the content of each node.
t_list *ft_lstmap(t_list *lst, void *(*f)(void *), void (*del)(void *));	Creates a new list by applying function f to each node’s content. Uses del to free memory if allocation fails.

ft_printf

Function	Description
int ft_printf(const char *s, ...);	Custom implementation of printf. Parses the format string s and prints arguments accordingly.

get_next_line

Function	Description
char *get_next_line(int fd);	Reads from the file descriptor fd and returns the next line, including the terminating newline character if present. Returns NULL when there are no more lines to read or on error.

Instructions

Build the library

Run:

make

This compiles all source files into object files and archives them into a static library, libft.a.

Using the library

Run the following command with your main.c:

cc -Wall -Wextra -Werror -o my_program main.c libft.a

Then, to run the program:

./my_program

Resources

• Makefile tutorial
• Linus man pages
• How to Structure C Projects