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Libft - @42Born2Code

My implementation of some of the Standard C Library functions including some additional ones.


What is libft?

Libft is an individual project at 42 that requires us to re-create some standard C library functions including some additional ones that can be used later to build a library of useful functions for the rest of the program.

Disclaimer: Reinventing the wheel is bad, 42 makes us do this just so we can have a deeper understanding of data structures and basic algorithms. At 42 we're not allowed to use some standard libraries on our projects, so we have to keep growing this library with our own functions as we go farther in the program.

What's in it?

As you can see from the Project instructions, there are 4 sections:

  1. Libc Functions: Some of the standard C functions
  2. Additional functions: Functions 42 deems will be useful for later projects
  3. Bonus Functions: Functions 42 deems will be useful for linked list manipulation
  4. Personal Functions: Functions I believe will be useful later. Documented here.
Libc functions Additional functions Bonus Functions Personal Functions
memset ft_memalloc ft_lstnew ft_capitalize
bzero ft_memdel ft_lstdelone ft_countwords
memcpy ft_strnew ft_lstdel ft_islower
memccpy ft_strdel ft_lstadd ft_isupper
memmove ft_strclr ft_lstiter ft_strndup
memchr ft_striter ft_lstmap ft_lst_reverse
memcmp ft_striteri ft_realloc
strlen ft_strmap ft_strjoinch
strdup ft_strmapi ft_strnchr
strcpy ft_strequ ft_copyuntil
strncpy ft_strnequ ft_strstartswith
strcat ft_strsub ft_intlen
strlcat ft_strjoin ft_strendswith
strchr ft_strtrim ft_pathjoin
strrchr ft_strsplit ft_lstaddback
strstr ft_itoa get_next_line
strnstr ft_putchar ft_putnstr
strcmp ft_putstr ft_strreplace
strncmp ft_putendl ft_isemptystr
atoi ft_putnbr ft_strsplitall
isalpha ft_putchar_fd ft_countwordsall
isdigit ft_putstr_fd ft_freestrarr
isalnum ft_putendl_fd ft_strjoincl
isascii ft_putnbr_fd ft_strjoinchcl
isprint ft_count2darray
toupper ft_strarrmax
tolower ft_get_parent_path


  • Most of the the files and function names are namespaced with an ft in front. It stands for Fourty Two
  • The project instructions require that we put all the source files in the root directory but for the sake of this Github repo, I separate them into sub folders.
  • I update this list almost every month with new personal functions. If you don't know what a function does, refer to the Wiki, where I document all my personal functions.

My code is not the best, but it passed all the 42 tests successfully.

How does it work?

The goal is to create a library called libft.a from the source files so I can later use that library from other projects at 42.

To create that library, after downloading/cloning this project, cd into the project, copy all the files from the sub folders to the root directory and finally, call make:

git clone
cd libft
make copy

You should see a libft.a file and some object files (.o).

Now to clean up (removing the .o files and the .c files from the root), call make clean

WARNING: make clean will delete all your files from your root directory. Do not run it if you're using the Makefile file. This is why I added the Makefile-sample file.

How do I use the library?

I added an example file called example.c, it's using the function ft_putstr to print "DON'T PANIC" to the screen.

If you try to compile it with gcc using gcc example.c you will get an undefined symbol error for ft_putstr.

You have to tell the file where your library resides and which library it is using:

gcc example.c -L. -lft

-L takes the path to your library. . in this case
-l takes the name of your library. This is the set of characters that come after lib in your library name.

That's it. Now run it using ./a.out

How do I test it? How do I test my own implementations?

To test the code we're going to be using @alelievr's Libft Unit Test. There are some good others but I'll only be covering this one.

1. To test the code in this repo

  1. Clone this repo and cd into it, make sure it's called libft:

     git clone
     cd libft/
  2. Copy all the source files to the root directory:

     make copy
  3. Run Make so you can build the library:

  4. Go back to the root directory and download @alelievr's Libft Unit Test:

     cd ..
     git clone
  5. Go into the test folder and run the test:

     cd libft-unit-test/
     make f

If you did everything correctly you should get a cool list of tests showing you the function names and if they passed or not.

2. To test your own code

You might want to have a go at this project too. If you've never heard of Makefiles, don't worry, you don't have to learn about it now. So go ahead and follow those steps:

  1. Create a directory for your project, make sure you call it libft:

     mkdir libft
  2. Clone this repo (don't name it libft) and copy the Makefile-sample as Makefile and libft.h to your own project:

     git clone r4-libft
     cp r4-libft/Makefile-sample libft/Makefile
     cp r4-libft/libft.h libft/
  3. Go to your project, read the instructions for the function you want to create, code it and uncomment it from the Makefile:

     cd libft
     vim ft_memset.c
     vim Makefile

    As an example, after creating ft_memset as your first function, you go into the Makefile, remove the # in front of FILES, remove the \ at the end of ft_memset and add a # in front of ft_bzero.

    If it still looks complicated, DON'T PANIC, just ask me :)

  4. Run Make so you can build the library:

  5. Go back to the root directory and download @alelievr's Libft Unit Test:

     cd ..
     git clone
  6. Go into the test folder and run the test:

     cd libft-unit-test/
     make f

That's it! If you're having some problems, just send me a tweet. If you think your problem is due to my code or this README, create a new issue. I'll definitely check it out.

Example usage

This is a list of my projects that use Libft extensively:





My implementation of some of the Standard C Library functions including some additional ones.



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