get_next_line.c

/* ************************************************************************** */
/*                                                                            */
/*                                                        :::      ::::::::   */
/*   get_next_line.c                                    :+:      :+:    :+:   */
/*                                                    +:+ +:+         +:+     */
/*   By: taretiuk <taretiuk@student.42.fr>          +#+  +:+       +#+        */
/*                                                +#+#+#+#+#+   +#+           */
/*   Created: 2024/01/23 10:49:23 by psulzyck          #+#    #+#             */
/*   Updated: 2024/02/12 15:39:11 by taretiuk         ###   ########.fr       */
/*                                                                            */
/* ************************************************************************** */

#include "get_next_line.h"

//read_line function read file till the \n character, store it in buf 
//and concatenate with the string stored in the static variable 
//written in previous call. Why we dont free buf: read 
//system call does not append data to the buffer; 
//instead, it overwrites the existing content of the buffer 
//with the newly read data.

static char	*read_line(int fd, char *buf, char *backup)
{
	ssize_t		i;
	char		*char_temp;

	i = 1;
	while (i > 0)
	{
		i = read(fd, buf, BUFFER_SIZE);
		if (i == -1)
			return (0);
		else if (i == 0)
			break ;
		buf[i] = '\0';
		if (backup == NULL)
		{
			backup = ft_strdup("");
		}
		char_temp = backup;
		backup = ft_strjoin(char_temp, buf);
		free(char_temp);
		char_temp = NULL;
		if (ft_strchr (buf, '\n'))
			break ;
	}
	return (backup);
}

//extract function extract the substring from the string
//returned by read_line function. it statrs extraction from 
//the next to the \n character (count + 1) and goes
//till the end of thistring

static char	*extract(char *line)
{
	size_t	count;
	char	*rest;

	count = 0;
	while (line[count] != '\n' && line[count] != '\0')
		count++;
	if (line[count] == '\0' || line[1] == '\0')
		return (0);
	rest = ft_substr(line, count + 1, ft_strlen(line) - count);
	if (rest == NULL || *rest == '\0')
	{
		free(rest);
		rest = NULL;
	}
	line[count + 1] = '\0';
	return (rest);
}

char	*get_next_line(int fd)
{
	char		*line;
	char		*buf;
	static char	*backup;

	if (fd == -1 || BUFFER_SIZE <= 0 || read(fd, 0, 0) < 0)
	{
		free(backup);
		backup = NULL;
		return (0);
	}
	buf = (char *)malloc(sizeof(char) * (BUFFER_SIZE + 1));
	if (!buf)
		return (0);
	line = read_line(fd, buf, backup);
	free(buf);
	buf = NULL;
	if (!line)
	{
		backup = NULL;
		return (NULL);
	}
	backup = extract(line);
	return (line);
}