ygor-sena / 42cursus-get-next-line

The second project of 42 curriculum asks students to implement a function that returns a line read from one or more file descriptors.

📣 About the project

Because reading a line from a fd is way too tedious, this project is about creating your own function that returns a line read from one file descriptor or more, if you consider the bonus project requirement. The function get_next_line() returns NULL, if there is nothing else to read or if an error occurred. It should work as expected both when reading a file and when reading from the standard output.

The main objetive of this project is to make students learn about static variables.

📈 How it was implemented

There are many ways to solve the problem stated. Either using an array or a singly linked list as a data structure. I decided to implement the last one because it was an opportunity to see how linked list are used.

The project contains six files. The ones that ends with _bonus are the bonus project that reads a line from two or more file descriptors at the same time. To sum up,

• get_next_line.h: contains the prototypes of all necessary functions to the project.
• get_next_line.c: it has five functions. They are:
  • get_next_line(): it's the project main function. It reads a line, saves the content and joins the line when it matches an EOF (end of file) or '\n' (new line break);
  • read_line(): reads a line at a max length of BUFFER_SIZE, which is defined at compilation time. If BUFFER_SIZE is not defined, the program sets the standard buffer value to 1024;
  • is_new_line(): checks whether the chunk read is a new line (i. e., it has \n) or not. It returns one if true and zero if false;
  • create_line(): creates a line by joining read buffer sized chunks of a line until EOF or \n is encountered;
  • refactor_line(): if a buffer sized chunk has \n, the function will save the content after \n to create the next line of the file descriptor by the time the get_next_line() function is called again. That's the reason why we need a static variable, the information isn't lost by the time the function ends.
• get_next_line_utils.c: implements helper functions to manipulate heap(or dynamic) memory and singly linked lists.

⚒️ How to use the project

To use the get_next_line() in your project it's necessary to include the three files mentioned above to be compiled, either the mandatory or the bonus files, and be sure to include the following flags:

$> gcc -Wall -Wextra -Werror -D BUFFER_SIZE=<length> <files>.c

Where <length> can be substituted by the number of bytes read at a time into the buffer for the read function. If BUFFER_SIZE is not defined, it will be defined to 1024 as standard value for the buffer size.

To reference the get_next_line() function inside your project, don't forget to add the header:

#include "get_next_line.h"

If you want to use the mandatory project, that is. If you want to use the bonus project to read multiple file descriptors, add the header:

#include "get_next_line_bonus.h"

📖 References

• Acelera GNL by rodsmade.
• To test the project and check for memory leaks, I used the gnlTester, made by jgambard.