get_next_line — File Descriptor Line Reader in C

42 Urduliz — Common Core project

A C function that reads a single line from a file descriptor each time it is called — like fgets but for any file descriptor (files, stdin, sockets).

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Prototype

char *get_next_line(int fd);

Returns the next line (including \n) or NULL on EOF or error. Calling it in a loop reads the entire file line by line.

Usage

#include "get_next_line.h"

int fd = open("file.txt", O_RDONLY);
char *line;

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

How It Works

Uses a static buffer to keep leftover data between calls. Reads in chunks of BUFFER_SIZE bytes (compile-time configurable), splits on \n, and returns one line at a time.

cc -D BUFFER_SIZE=42 get_next_line.c get_next_line_utils.c main.c

Skills

C Static Variables File Descriptors Memory Management Buffer Management

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Academic Integrity

This repository is shared for educational and portfolio purposes only.

For 42 students:

• Do not copy this code for your own project submissions
• Use it as a reference to understand concepts and approaches
• Write your own original solution — that is the only way to actually learn

42's core values are learning through practice, peer collaboration, and genuine problem-solving.

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License

MIT — see LICENSE for details. Copyright (c) 2026 Eneko Muñoz Bordona