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

Libft

Description

Libft is my first C library. The goal is to understand how standard C functions work by rewriting them, and to build reusable utilities for future 42 projects. It is compiled into the static library libft.a and follows the 42 Norm.

Result: this project was validated with a score of 100/100.

Instructions

make          # builds libft.a at the root of the repository
make clean    # removes the object files
make fclean   # removes the object files and libft.a
make re       # fclean + all

Use it in a program with:

#include "libft.h"

cc -Wall -Wextra -Werror main.c -I. -L. -lft

Library description

libft.a is a static library: the ar command packs all the object files into one archive, and the linker copies into a program only the functions that the program uses. The library has 43 functions in three parts, declared in libft.h:

1. Libc functions: my own versions of standard C functions, with the ft_ prefix and the same prototypes and behavior as the originals.
2. Additional functions: string, conversion and output functions that are not in the libc, or that are a different version of one.
3. Linked lists: functions that work on the t_list structure (content and next).

Technical choices:

• The functions copied from the libc behave like the originals, including crashing on NULL where the original does (undefined behavior). The functions with no libc original check their pointers.
• ft_memmove copies forward or backward depending on the position of the two areas, so overlapping memory is handled correctly.
• ft_calloc returns NULL if nmemb * size overflows.
• ft_split and ft_lstmap free everything they allocated before a failure and return NULL, so a failed allocation does not leak.
• ft_lstadd_front and ft_lstadd_back accept an empty list: the new node becomes the head.

Functions

Part 1 - Libc functions

Function	What it does
ft_isalpha	Returns 1 if c is a letter, 0 otherwise.
ft_isdigit	Returns 1 if c is a digit, 0 otherwise.
ft_isalnum	Returns 1 if c is a letter or a digit, 0 otherwise.
ft_isascii	Returns 1 if c is an ASCII character (0 to 127), 0 otherwise.
ft_isprint	Returns 1 if c is a printable character, 0 otherwise.
ft_toupper	Converts a lowercase letter to uppercase.
ft_tolower	Converts an uppercase letter to lowercase.
ft_strlen	Returns the length of a string.
ft_strlcpy	Copies a string into a buffer of a given size and always terminates it.
ft_strlcat	Appends a string to another, within a given buffer size.
ft_strchr	Returns a pointer to the first occurrence of a character in a string.
ft_strrchr	Returns a pointer to the last occurrence of a character in a string.
ft_strncmp	Compares two strings, up to n characters.
ft_strnstr	Finds a substring inside a string, within the first len characters.
ft_strdup	Returns a newly allocated copy of a string.
ft_memset	Fills a memory area with a byte.
ft_bzero	Sets a memory area to zero.
ft_memcpy	Copies n bytes from one memory area to another.
ft_memmove	Copies n bytes, and works correctly when the areas overlap.
ft_memchr	Finds the first occurrence of a byte in a memory area.
ft_memcmp	Compares two memory areas byte by byte.
ft_calloc	Allocates memory for an array and sets it to zero.
ft_atoi	Converts the beginning of a string to an int.

Part 2 - Additional functions

Function	What it does
ft_substr	Returns a new substring of s, from index start, of at most len characters.
ft_strjoin	Returns a new string made of s1 followed by s2.
ft_strtrim	Returns a copy of s1 without the characters of set at the start and at the end.
ft_split	Splits a string with a delimiter character and returns a NULL-terminated array of strings.
ft_itoa	Converts an integer to a new string.
ft_strmapi	Applies a function to each character (with its index) and returns the new string.
ft_striteri	Applies a function to each character (with its index), directly on the string.
ft_putchar_fd	Writes a character to a file descriptor.
ft_putstr_fd	Writes a string to a file descriptor.
ft_putendl_fd	Writes a string followed by a newline to a file descriptor.
ft_putnbr_fd	Writes an integer to a file descriptor.

Part 3 - Linked lists

Function	What it does
ft_lstnew	Creates a new node with the given content.
ft_lstadd_front	Adds a node at the beginning of the list.
ft_lstadd_back	Adds a node at the end of the list.
ft_lstsize	Counts the nodes of the list.
ft_lstlast	Returns the last node of the list.
ft_lstdelone	Frees the content of a node with del, then frees the node.
ft_lstclear	Deletes a node and all the nodes after it, then sets the list to NULL.
ft_lstiter	Applies a function to the content of every node.
ft_lstmap	Builds a new list from the results of a function applied to each node.

Resources

• Linux man pages, section 3 (man 3 strlen, man 3 memmove, ...)
• The GNU C Library reference manual
• Kernighan and Ritchie, The C Programming Language
• The 42 Norm
• Stack Overflow, W3Schools and GeeksforGeeks, for C concepts and examples
• YouTube tutorials, for pointers, memory and linked lists
• AI assistant: used to understand new concepts and find learning resources