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Get Next Line

Reading a line from a fd is way too tedious

This project is about programming a function that returns a line read from a file descriptor

Goals

This project will not only allow you to add a very convenient function to your collection, but it will also make you learn a highly interesting new concept in C programming: static variables.

Mandatory Part

Key Value
Function name get_next_line
Prototype char *get_next_line(int fd);
Turn in files get_next_line.c, get_next_line_utils.c, get_next_line.h
Parameters fd: The file descriptor to read from
Return value Read line: correct behavior
NULL: there is nothing else to read, or an error occurred
External functions read, malloc, free
Description Write a function that returns a line read from a file descriptor
  • Repeated calls (e.g., using a loop) to your get_next_line() function should let you read the text file pointed to by the file descriptor, one line at a time.
  • Your function should return the line that was read. If there is nothing else to read or if an error occurred, it should return NULL.
  • Make sure that your function works as expected both when reading a file and when reading from the standard input.
  • Please note that the returned line should include the terminating \n character, except if the end of file was reached and does not end with a \n character.
  • Your header file get_next_line.h must at least contain the prototype of the get_next_line() function.
  • Add all the helper functions you need in the get_next_line_utils.c file.

ℹ️ A good start would be to know what a static variable is.

  • Because you will have to read files in get_next_line(), add this option to your compiler call: 
     -D BUFFER_SIZE=n
    It will define the buffer size for read(). The buffer size value will be modified by your peer-evaluators and the Moulinette in order to test your code.

⚠️ We must be able to compile this project with and without the -D BUFFER_SIZE flag in addition to the usual flags You can choose the default value of your choice.

  • You will compile your code as follows (a buffer size of 42 is used as an example): 
     cc -Wall -Wextra -Werror -D BUFFER_SIZE=42 <files>.c
  • We consider that get_next_line() has an undefined behavior if the file pointed to by the file descriptor changed since the last call whereas read() didn't reach the end of file.
  • We also consider that get_next_line() has an undefined behavior when reading a binary file. However, you can implement a logical way to handle this behavior if you want to.

💡 Does your function still work if the BUFFER_SIZE value is 9999? If it is 1? 10000000? Do you know why?

ℹ️ Try to read as little as possible each time get_next_line() is called. If you encounter a new line, you have to return the current line.
Don't read the whole file and then process each line.

Forbidden

  • You are not allowed to use your libft in this project.
  • lseek() is forbidden.
  • Global variables are forbidden.

Bonus Part

This project is straightforward and doesn't allow complex bonuses. However, we trust your creativity. If you completed the mandatory part, give a try to this bonus part.

Here are the bonus part requirements:

  • Develop get_next_line() using only one static variable.
  • Your get_next_line() can manage multiple file descriptors at the same time. For example, if you can read from the file descriptors 3, 4 and 5, you should be able to read from a different fd per call without losing the reading thread of each file descriptor or returning a line from another fd.
    It means that you should be able to call get_next_line() to read from fd 3, then fd 4, then 5, then once again 3, once again 4, and so forth.

Append the _bonus.[c\h] suffix to the bonus part files.
It means that, in addition to the mandatory part files, you will turn in the 3 following files:

  • get_next_line_bonus.c
  • get_next_line_bonus.h
  • get_next_line_utils_bonus.c

ℹ️ When writing your tests, remember that:

  1. Both the buffer size and the line size can be of very different values.
  2. A file descriptor does not only point to regular files.
    Be smart and cross-check with your peers. Prepare a full set of diverse tests for defense.

Once passed, do not hesitate to add your get_next_line() to your libft.