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get_next_line - @42Born2Code

A C function that reads any valid file line by line until the end.


What is get_next_line?

get_next_line is an individual project at 42 that basically reads a file line by line.

Disclaimer: There are so many easier methods of doing this by using standard C functions. But the goal here is to be able to do it by using any functions from my libft and only the standard functions read, malloc and free.

Why would I use/try it?

You probably will never have to use this function if you are not a 42 student. The goal is to get better at C. As I said above, you can only use those three standard library functions:

  • read
  • malloc
  • free

So it makes the project harder. But you can also use functions from your personal library.

After finishing this project, you'll definitely learn some more about static variables, pointers, arrays, linked lists (if you decide to do the bonus part), dynamic memory allocation and file manipulation.

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

How do I use it?

I added a main file called main.c, it takes a file name as an argument, opens it and passes the file descriptor (fd) to get_next_line until get_next_line returns -1 or 0.

Note: get_next_line returns -1, 0, 1 depending on wether an error has occurred, the reading has been completed or a line has been read respectively.

Alright, so first of all, download/clone this repo:

git clone

Get into it and build the library:

cd get_next_line
make -C libft/

Give it some time to compile all the files.

Build the executable:

gcc -Wall -Wextra -Werror -I./libft/includes/ -L./libft -lft -o gnl get_next_line.c main.c

-I tells the compiler where your library header files are. ./libft/includes/ in this case

-L tells it where your library resides. ./libft here

-l takes the name of your library. This is the set of characters that come after lib in your library name.

NOTE: -L and -l might look a little bit too much, you could replace those flags with libft/libft.a if you want.

Alright, the last command created a gnl executable in your directory. Now test it with:

./gnl m83.txt

It should read the whole file to you. Kinda like a basic cat implementation.

NOTE: The lyrics in the text file are from Claudia Lewis by M83 ;)

How do I try it out?

If you are a beginner to intermediate programmer and want to hone your skills in C, I highly recommend you to give this project a try.

To do that, you just have to read the project instructions, some stuffs on there might be confusing if you are not a 42 student, but don't mind them. Just make sure you use only read, malloc, free as your only available standard library functions and my/your libft functions.

I created a folder named gnl-sample for you, it has the required files plus the testing files.

All you need to do now is cd into it and clone my Libft, if you already made your own Libft, perfect, use it:

cd gnl-sample
git clone

Build the libft library and you're done:

make -C libft/ copy
make -C libft/
make -C libft/ clean

NOTE: Just a reminder, in my Libft repo, the header file libft.h is in the libft/ directory, not libft/includes/, so when you build your project, use this instead:

gcc -Wall -Wextra -Werror -I./libft/ -L./libft -lft -o gnl get_next_line.c main.c

The instructions are clear enough, so I won't add anything else. If you have any questions, feel free to ask me.

How do I test my own code?

You can do as above and use the main file I added, just make sure you use your own get_next_line.c file. This is a pretty rudimentary test, if you want to try some deep tests, let me introduce you to the amazing 42FileChecker by @jgigault.

Assuming you read the project instructions and coded your own get_next_line

  1. Go back to the root directory and download @jgigault's 42FileChecker:

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

     cd 42FileChecker

At the time of writing, @jgigault is looking for a maintainer for 42FC, so he displays a message on startup, dismiss it with 1 or contact him if you think you can help.

Then press 5 to select tests for get_next_line, press 1 to install moulitest as an external repo, then 1 to configure the tests, now you handle the path to your get_next_line and then choose which test to run on your project.

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.





A C function that reads any valid file line by line until the end.



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