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

Libft — Your very first own library

Description

First project of the 42 curriculum. The goal is to reimplement a set of standard C library functions from scratch, then add custom utility functions not found in the libc. The result is a static library libft.a that can be reused throughout the entire 42 curriculum.

The project is split into three parts: libc reimplementations, additional string/memory utilities, and linked list manipulation functions.

Compilation

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

To use the library in another project:

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

Library Reference

Part 1 — Libc functions

Reimplementations of standard libc functions. All use the ft_ prefix (e.g. strlen → ft_strlen). No external functions used except where noted.

Function	Prototype	Description
ft_isalpha	int ft_isalpha(int c)	Returns 1 if c is alphabetic, 0 otherwise
ft_isdigit	int ft_isdigit(int c)	Returns 1 if c is a digit, 0 otherwise
ft_isalnum	int ft_isalnum(int c)	Returns 1 if c is alphanumeric, 0 otherwise
ft_isascii	int ft_isascii(int c)	Returns 1 if c is in ASCII range, 0 otherwise
ft_isprint	int ft_isprint(int c)	Returns 1 if c is printable, 0 otherwise
ft_strlen	size_t ft_strlen(const char *s)	Returns the length of s
ft_memset	void *ft_memset(void *b, int c, size_t len)	Fills len bytes of b with c
ft_bzero	void ft_bzero(void *s, size_t n)	Zeroes n bytes of s
ft_memcpy	void *ft_memcpy(void *dst, const void *src, size_t n)	Copies n bytes from src to dst
ft_memmove	void *ft_memmove(void *dst, const void *src, size_t len)	Safe copy handling overlapping areas
ft_strlcpy	size_t ft_strlcpy(char *dst, const char *src, size_t sz)	Size-bounded string copy
ft_strlcat	size_t ft_strlcat(char *dst, const char *src, size_t sz)	Size-bounded string concatenation
ft_toupper	int ft_toupper(int c)	Converts c to uppercase
ft_tolower	int ft_tolower(int c)	Converts c to lowercase
ft_strchr	char *ft_strchr(const char *s, int c)	First occurrence of c in s
ft_strrchr	char *ft_strrchr(const char *s, int c)	Last occurrence of c in s
ft_strncmp	int ft_strncmp(const char *s1, const char *s2, size_t n)	Compares up to n bytes of two strings
ft_memchr	void *ft_memchr(const void *s, int c, size_t n)	Finds c in the first n bytes of s
ft_memcmp	int ft_memcmp(const void *s1, const void *s2, size_t n)	Compares n bytes of two memory areas
ft_strnstr	char *ft_strnstr(const char *h, const char *n, size_t len)	Finds n in h within len bytes
ft_atoi	int ft_atoi(const char *str)	Converts a string to an integer
ft_calloc	void *ft_calloc(size_t nmemb, size_t size)	Allocates zero-initialised memory (malloc)
ft_strdup	char *ft_strdup(const char *s)	Returns a heap-allocated copy of s (malloc)

Part 2 — Additional functions

Custom functions not present in the libc, or present in a different form.

Function	Prototype	Description
ft_substr	char *ft_substr(char const *s, unsigned int start, size_t len)	Returns a substring of s starting at start, max length len
ft_strjoin	char *ft_strjoin(char const *s1, char const *s2)	Concatenates s1 and s2 into a new string
ft_strtrim	char *ft_strtrim(char const *s1, char const *set)	Trims characters in set from both ends of s1
ft_split	char **ft_split(char const *s, char c)	Splits s on delimiter c, returns NULL-terminated array
ft_itoa	char *ft_itoa(int n)	Converts integer n to a string (handles negatives)
ft_strmapi	char *ft_strmapi(char const *s, char (*f)(unsigned int, char))	Applies f to each character, returns new string
ft_striteri	void ft_striteri(char *s, void (*f)(unsigned int, char*))	Applies f to each character in place (by address)
ft_putchar_fd	void ft_putchar_fd(char c, int fd)	Writes character c to file descriptor fd
ft_putstr_fd	void ft_putstr_fd(char *s, int fd)	Writes string s to file descriptor fd
ft_putendl_fd	void ft_putendl_fd(char *s, int fd)	Writes string s followed by \n to fd
ft_putnbr_fd	void ft_putnbr_fd(int n, int fd)	Writes integer n to file descriptor fd

Part 3 — Linked list (bonus)

Functions operating on the t_list singly linked list structure defined in libft.h:

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

Function	Prototype	Description
ft_lstnew	t_list *ft_lstnew(void *content)	Creates a new node with content, next set to NULL
ft_lstadd_front	void ft_lstadd_front(t_list **lst, t_list *new)	Prepends new to the list
ft_lstsize	int ft_lstsize(t_list *lst)	Returns the number of nodes in the list
ft_lstlast	t_list *ft_lstlast(t_list *lst)	Returns the last node of the list
ft_lstadd_back	void ft_lstadd_back(t_list **lst, t_list *new)	Appends new to the list
ft_lstdelone	void ft_lstdelone(t_list *lst, void (*del)(void *))	Frees one node's content with del, then frees the node
ft_lstclear	void ft_lstclear(t_list **lst, void (*del)(void *))	Frees all nodes and sets the pointer to NULL
ft_lstiter	void ft_lstiter(t_list *lst, void (*f)(void *))	Applies f to each node's content
ft_lstmap	t_list *ft_lstmap(t_list *lst, void *(*f)(void *), void (*del)(void *))	Creates a new list by applying f to each node's content

Rules

• Written in C, compiled with cc -Wall -Wextra -Werror
• No global variables
• Helper functions must be static
• All files at the root of the repository
• Library created with ar — libtool is forbidden
• No unused files
• No memory leaks
• Norm compliant (bonus files in _bonus.c/.h)
• No -std=c99 flag — do not use the restrict qualifier in prototypes

Testing

Compile with debug flags

cc -g -w main.c -I../ -L../ -lft

Flag breakdown:

• -g — include debug symbols (useful with valgrind/gdb)
• -w — suppress all compiler warning messages
• -I../ — add parent directory to include-file search path (finds libft.h)
• -L../ — add parent directory to library search path (finds libft.a)
• -lft — link against libft.a

Check for memory leaks

valgrind --leak-check=full \
         --show-leak-kinds=all \
         --track-origins=yes \
         --verbose \
         --log-file=valgrind-out.txt \
         ./a.out

Resources

• man pages — libc functions
• cplusplus.com — C standard library reference
• glibc vs BSD libc differences
• Understanding static libraries — ar command
• Linked lists in C
• Makefile example — 42 project
• Libft test suite — pulgamecanica