Get Next Line

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

Description

Get Next Line is a C project that consists of implementing a Get_next_line function. The goal of this function is to read from file descriptor and return one line at atime, ending with new line character (\n) if present, or NULL when nothing left to read ot an error occurs.

The project focuses on:

• Using the read() system call
• Managing memory safely (no leaks)
• Handle static variables
• Supporting different BUFFER_SIZE value
• Managing multiple file descriptor in Bonus part

Instructions

How to run project

Use CC compiler with the required flags:

cc -Wall -Wextra -Werror get_next_line.c get_next_line_utils.c main.c && ./a.out

Note:

Flags to any warning be come error

Using customBUFFER_SIZE marco

cc -Wall -Wextra -Werror get_next_line.c get_next_line_utils.c main.c -D BUFFER_SIZE=1337 && ./a.out

To verify memory leaks use Valgrind

cc -Wall -Wextra -Werror get_next_line.c get_next_line_utils.c main.c -D BUFFER_SIZE=42 && valgrind -s --track-origins=yes  --leak-check=full ./a.out

Note:

-s for summary error report --track-origins=yes to track uninitialized values --leak-check=full provides detailed information

Usage examples

File main example to test Mandatory part

#include "get_next_line.h"
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>

int main()
{
    int fd = open("text.txt", O_RDONLY);

    char *line;

    line = get_next_line(fd);
    printf("%s", line);
    free(line);

    line = get_next_line(fd);
    printf("%s", line);
    free(line);

    close(fd);
}

File main example to test Bonus part (Multiple file descriptor)

#include "get_next_line_bonus.h"
#include <unistd.h>
#include <stdio.h>
#include <fcntl.h>

int main()
{
    int fd = open("text.txt", O_RDONLY);
    int fd2 = open("text2.txt", O_RDONLY);
    int fd3 = open("text3.txt", O_RDONLY);

    char *line;

    line = get_next_line(fd);
    printf("%s", line);
    free(line);

    line = get_next_line(fd2);
    printf("%s", line);
    free(line);

    line = get_next_line(fd2);
    printf("%s", line);
    free(line);

    line = get_next_line(fd3);
    printf("%s", line);
    free(line);

    line = get_next_line(fd2);
    printf("%s", line);
    free(line);

    line = get_next_line(fd3);
    printf("%s", line);
    free(line);

    line = get_next_line(fd);
    printf("%s", line);
    free(line);

    close(fd);
}

Resources

Website and books

Static variables in C geeksforgeeks

read() system call documentation opengroup

File descriptor linux programming interface book

File offset and read behavior IC221 - Systems Programming and linux programming interface book

How I use AI

AI tool were used only to generated test file and simple input data.

Algorithm Explanation and justification

1. A static variable (line) use to store leftover data between calls.
2. Memory is allocate for a buffer (buf) of size BUFFER_SIZE + 1 to store data read by read().
3. The function read from file descriptor until:
   1. A newline (\n) is found, or
   2. read() return 0 (end of file), or
   3. An error occurs.
4. Each buffer read is appended to static variable using a custom ft_strjoin().
5. When a newline detected:
   1. A substring from the beginning up to the newline using ft_substr() and returned.
   2. The remaining data after the newline is kept in the static variable (line) for the next call
6. If the end of file is reached and no newline:
   1. The remaining content is returned.
   2. The static variable is freed using free().
7. All allocated memory is carefully freed to avoid leaks.

Feature

• Return one line at time from file descriptor
• Handle macro BUFFER_SIZE
• No memory leaks
• Bound: support multiple file descriptor
• Handle when malloc() and read() filed