README_GNL.md

📜 Get Next Line

Get Next Line (GNL) is a 42 project focused on reading text from a file descriptor line by line, regardless of the buffer size or line length.
The goal is to understand how file reading works in C, including buffers, static variables, and memory management.

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🧠 Purpose

The project aims to:

• Understand how to manage file descriptors
• Learn how to store and reuse data between function calls using static variables
• Handle dynamic memory allocation safely
• Work efficiently with any BUFFER_SIZE
• Prepare for more advanced I/O and parsing projects

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⚙️ Features

Mandatory Part

• Reads one line from a file descriptor each time it’s called
• Returns NULL when there is nothing else to read or an error occurs
• Supports any BUFFER_SIZE defined at compile time
• Efficient memory handling (no leaks, no overflows)

Bonus Part

• Handles multiple file descriptors at the same time
• Each file descriptor keeps its own buffer state independently
• Works with standard input (stdin) as well as regular files

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🧩 Function Prototypes

Mandatory

char *get_next_line(int fd);

Bonus

char *get_next_line(int fd);

(The same prototype — but must handle multiple file descriptors)

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📂 Project Structure

get_next_line/
├── get_next_line.c
├── get_next_line_utils.c
├── get_next_line.h
├── get_next_line_bonus.c
├── get_next_line_utils_bonus.c
├── get_next_line_bonus.h
└── main.c (for testing)

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🧮 Compilation & Usage

Compile (Mandatory)

cc -Wall -Wextra -Werror get_next_line.c get_next_line_utils.c main.c -D BUFFER_SIZE=42

Compile (Bonus)

cc -Wall -Wextra -Werror get_next_line_bonus.c get_next_line_utils_bonus.c main.c -D BUFFER_SIZE=42

Run Example

./a.out

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🧰 Example

Example file (text.txt):

Hello world!
42 Network
Get Next Line Project

Example program (main.c):

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

int main(void)
{
    int fd = open("text.txt", O_RDONLY);
    char *line;

    while ((line = get_next_line(fd)) != NULL)
    {
        printf("%s", line);
        free(line);
    }
    close(fd);
    return 0;
}

Output:

Hello world!
42 Network
Get Next Line Project

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🧱 Key Concepts

Concept	Description
Static variable	Keeps leftover data between function calls
Buffer	Temporarily holds data read from the file
Newline detection	Splits data until a `'
'` is found
File descriptor	An integer used to identify an open file
Memory safety	Each allocation must be freed properly

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🧪 Testing Tips

• Change BUFFER_SIZE to test performance and correctness
• Test with empty files, long lines, and multiple newlines
• Test reading from stdin using:

  cat file.txt | ./a.out

• Use Valgrind or leaks to check for memory leaks

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👨‍💻 Author

• Semih Kaynar — Developer
• 42 Istanbul 🇹🇷

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📜 License

This project is developed as part of the 42 curriculum and is intended for educational purposes only.