🚀 Get_Next_Line

My second project in 42 Common Core — let's goooooo (๑•̀ ᴗ•́)۷✧
A function that reads from a file descriptor, line by line, with dynamic memory management!

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📊 Project Overview

Metric	Details
📁 Project Name	get_next_line
🧠 Key Concepts	File descriptors, buffers, dynamic memory
🧩 Bonus Features	Support for multiple FDs
⏱️ Time Spent	~2 weeks
🔥 Difficulty	Medium – High

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🎯 Goals

Build a robust version of:

char *get_next_line(int fd);

That will:

• ✅ Read and return one line at a time
• ✅ Work with any valid file descriptor
• ✅ Handle multiple FDs (bonus)
• ✅ Use dynamic memory — no fixed-size line limits
• ✅ Preserve remaining buffer data between calls

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📚 Core Concepts & Skills

🔧 File Descriptors & Low-Level I/O

• Work with open, read, close
• Understand stdin, stdout, stderr
• 🔗 GeeksforGeeks - File Descriptors

🧵 Buffers & Persistent State

• Use a static buffer (stash) per FD to track leftover data
• Handle partial reads and newline detection

🧠 Dynamic Memory

• Use malloc, free, strjoin, strdup correctly
• Clean up to avoid memory leaks

🧰 String Utilities

Recreate or reuse:

• strchr → Find \n
• strdup → Duplicate memory
• strjoin, substr → Combine & extract string parts

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⚙️ Project Flow (How it works)

get_next_line(fd)
    ↓
[Read BUFFER_SIZE bytes]
    ↓
[Append to stash]
    ↓
[Search for newline '\n']
    ↓
[Extract line + update stash]
    ↓
Return line

Step	Description
✅ Validate input	Check for valid fd and buffer size
📥 Read from fd	Until newline or EOF
💾 Save remainder	Static stash retains leftover data
🧻 Extract line	Up to and including \n
🔚 Handle EOF	Return NULL when done

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🔧 Helper Functions

Function	Purpose
ft_strchr	Locate \n in stash
ft_strdup	Duplicate a string
ft_strjoin_free	Join stash and buffer, free old stash
ft_substr	Extract a substring

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🧪 Example Execution

Input file:

Hello\nWorld\n42\n

Call #	Returned Line	Stash After Call
1	Hello\n	World\n42\n
2	World\n	42\n
3	42\n	`` (empty)
4	NULL	EOF reached

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🔄 Memory & Flowchart

[read(fd) → BUFFER] → [append to stash]
       ↓
[find newline] → [split stash]
       ↓
[return line] + [keep leftover in static stash]

Tip: Use valgrind or leaks to verify no memory is left unfreed!

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🔍 Bonus: Multiple FDs

int fd1 = open("file1.txt", O_RDONLY);
int fd2 = open("file2.txt", O_RDONLY);

get_next_line(fd1); // reads from file1
get_next_line(fd2); // independently reads from file2

Your implementation must track separate stash buffers for each FD. Use something like a static array indexed by FD, or a custom linked list (if you're daring!).

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📦 Resources

• 42 Project Docs
• Repo: ayogun
• Repo: nickdotht
• Medium: Deep Dive #1
• Medium: Deep Dive #2
• YouTube: Line by Line

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✅ Checklist

• Reads 1 line at a time (with \n)
• Handles files of any size
• Supports multiple FDs (bonus)
• Uses only allowed functions
• No memory leaks
• Makefile with all required rules
• Clean, modular code (helpers, no spaghetti!)

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💬 Final Thoughts

get_next_line taught me how to:

• Think like the OS (I/O is tricky!)
• Work with static memory across function calls
• Build resilient and reusable logic in C
• Handle edge cases and memory carefully

Master this project, and buffer logic will never scare you again 😤

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Made with 💻, ⚔️ and lots of malloc debugging.

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