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

libft

Description

libft is a custom C library written as part of the 42 curriculum. The project recreates a set of standard libc functions and adds additional utilities that are frequently needed in C projects. It focuses on memory management, pointer logic, and writing clean, reusable code.

Goal

• Strengthen C fundamentals (pointers, arrays, strings, memory)
• Practice safe dynamic allocation and error handling
• Understand standard library behavior by re-implementing it
• Build a reusable library for future 42 projects
• Implement a Linked List API (creation, iteration, deletion, mapping)

Overview

Functions are grouped into three parts:

1. Libc Functions (re-implemented)
2. Additional Utilities
3. Linked List Functions

All functions are implemented from scratch (only standard headers are used).

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Instructions

Compile

make

This produces the static library: libft.a

Make Targets

• make clean → remove object files
• make fclean → remove objects + libft.a
• make re → rebuild everything

Use in a Project

Include the header:

#include "libft.h"

Compile with the library:

gcc -Wall -Wextra -Werror your_program.c libft.a -o your_program

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Detailed Library Description

Part 1 — Libc Functions (Re-implemented)

Character Classification & Conversion

• ft_isalpha → alphabetic check
• ft_isdigit → digit check
• ft_isalnum → alphanumeric check
• ft_isascii → ASCII check
• ft_isprint → printable check
• ft_toupper → convert to uppercase
• ft_tolower → convert to lowercase

String Functions

• ft_strlen → string length
• ft_strchr → first occurrence of a character
• ft_strrchr → last occurrence of a character
• ft_strncmp → compare up to n characters
• ft_strnstr → find substring within a bounded length
• ft_strlcpy → size-bounded copy (NUL-terminated when size > 0)
• ft_strlcat → size-bounded concatenation

Memory Functions

• ft_memset → fill memory with a byte value
• ft_bzero → set a memory region to zero
• ft_memcpy → copy memory (undefined for overlap)
• ft_memmove → copy memory (safe for overlap)
• ft_memchr → locate a byte in memory
• ft_memcmp → compare memory regions
• ft_calloc → allocate and zero-initialize memory

Conversion

• ft_atoi → string to integer
• ft_itoa → integer to string

Part 2 — Additional Utilities

String Manipulation

• ft_strdup → duplicate a string
• ft_substr → extract a substring
• ft_strjoin → join two strings into a new allocation
• ft_strtrim → trim characters from both ends
• ft_split → split a string by a delimiter
• ft_strmapi → map a function over a string (creates new string)
• ft_striteri → apply a function over a string in place

Output to File Descriptor

• ft_putchar_fd → write a character
• ft_putstr_fd → write a string
• ft_putendl_fd → write a string + newline
• ft_putnbr_fd → write an integer

Part 3 — Linked List Functions

• ft_lstnew → create a new node
• ft_lstadd_front → add node to the front
• ft_lstadd_back → add node to the back
• ft_lstsize → count nodes
• ft_lstlast → get last node
• ft_lstdelone → delete one node (using a del function)
• ft_lstclear → clear the entire list (deep free)
• ft_lstiter → apply a function to each node
• ft_lstmap → create a new list by applying a function (with cleanup on failure)

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Resources

Video

• Harvard CS50 (YouTube Playlist)

Official / Primary References

• Linux man-pages (function contracts & edge cases)
• GNU C Library Manual (glibc)
• Beej’s Guide to C (clear explanations)

C Standard Library References

• Tutorialspoint — C Programming
• Tutorialspoint — string.h overview
• cplusplus.com — cstring reference

Linked List

• GeeksforGeeks — What is a Linked List?

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AI Usage

I used AI as a learning assistant, not as a code generator.

• I created a dedicated AI workspace and added 42’s AI-related documents (e.g., We All Love ChatGPT and the Libft subject AI instructions) along with the Libft subject as reference notes.
• Workflow: I first tried to solve each problem on my own, then used AI to clarify concepts and double-check edge cases.
• AI helped me with: understanding function behavior (man-page level), comparing functions (e.g., memcpy vs memmove), generating test-case ideas, interpreting compiler/runtime error outputs during debugging, and reviewing potential memory leaks and edge cases.