This function is now part of Libft

Get-Next-Line

The Get Next Line project aims to create a function in C that reads and returns a line from a given file descriptor. This function is designed to handle various edge cases and should work efficiently even with varying buffer sizes. This project not only provides a useful function but also introduces the concept of static variables in C programming.

• Prototype: char *get_next_line(int fd)
• Parameters:
  • fd: The file descriptor to read from.
• Returns: A pointer to a string containing the next line from the file descriptor, or NULL if the end of the file is reached or an error occurs.

Features

• Read and return a single line from the file descriptor each time it is called, including standard input.
• Support multiple file descriptors simultaneously without losing the reading thread for each.
• Handle various buffer sizes defined at compile time using -D BUFFER_SIZE=n.
• Handle end-of-file correctly, and include the newline character in the returned line, except if the end-of-file is reached.
• Utilize only one static variable in the implementation.
• Properly free all heap-allocated memory.

File Handling

The fcntl.h and unistd.h libraries in C provides advanced file control operations.

open()

• Description: Open a file.
• Prototype: int open(const char *pathname, int flags);
  • Parameters:
    • pathname: Path to the file.
    • flags: Mode in which to open the file.
      • O_RDONLY: Open for reading only.
      • O_WRONLY: Open for writing only.
      • O_RDWR: Open for reading and writing.
      • O_CREAT: Create the file if it does not exist.
      • O_TRUNC: Truncate the file to length 0 if it exists.
      • O_APPEND: Write at the end of the file.
  • Returns: File descriptor on success, -1 on error.

read()

• Description: Read from a file.
• Prototype: ssize_t read(int fd, void *buf, size_t count);
  • Parameters:
    • fd: File descriptor to read from.
    • buf: Buffer to read data into.
    • count: Number of bytes to read.
  • Returns: Number of bytes read on success, -1 on error.

write()

• Description: Write to a file.
• Prototype: ssize_t write(int fd, const void *buf, size_t count);
  • Parameters:
    • fd: File descriptor to write to.
    • buf: Buffer containing data to write.
    • count: Number of bytes to write.
  • Returns: Number of bytes written on success, -1 on error.

close()

• Description: Close a file.
• Prototype: int close(int fd);
  • Parameters:
    • fd: File descriptor to close.
  • Returns: 0 on success, -1 on error.

Usage Example:

void	display(char *filename)
{
	int		fd;
	char	character;

	fd = open(filename, O_RDONLY);
	if (fd < 0)
		return (-1);
	while (read(fd, &character, 1))
		write(1, &character, 1);
	close(fd);
}

Static Variables

A static variable in C is a variable that retains its value between multiple function calls. It is initialized only once and exists for the lifetime of the program, but its scope is limited to the block in which it is defined.

void count_calls() {
    static int count = 0; // Static variable
    count++;
    printf("Function called %d times\n", count);
}

int main() {
    for (int i = 0; i < 5; i++) {
        count_calls();
    }
    return 0;
}

• Local Static Variables: Defined within a function and retain their value between calls to that function.
• Global Static Variables: Defined outside of all functions and are accessible only within the file in which they are declared.

Implementation

Get_next_line_utils.c

ft_isnewline

The ft_isnewline function checks if there is a newline character (\n) in the given buffer and returns its position if found. If the buffer is NULL or no newline character is present, it returns -1.

int	ft_isnewline(char *buffer)
{
	int	i;

	if (!buffer)
		return (-1);
	i = 0;
	while (buffer[i])
	{
		if (buffer[i] == '\n')
			return (i);
		i++;
	}
	return (-1);
}

Parameters:

• char *buffer: A pointer to the string buffer that will be checked for the presence of a newline character.

Functionality:

• Checks if the buffer is NULL. If it is, the function returns -1 to indicate an error.
• Iterates through each character in the buffer.
• If a newline character (\n) is encountered, the function returns the index of that character within the buffer.
• If no newline character is found after checking the entire buffer, the function returns -1, indicating the absence of a newline character.

ft_strlen

The ft_strlen function calculates the length of a given string by counting the number of characters until the null terminator (\0). If the string is NULL, it returns 0.

int	ft_strlen(char *str)
{
	int	i;

	i = 0;
	if (!str)
		return (0);
	while (str[i])
		i++;
	return (i);
}

Parameters:

• char *str: A pointer to the string whose length is to be calculated.

Functionality:

• Initializes an integer i to 0 to serve as a counter for the string length.
• Checks if the string str is NULL. If it is, the function returns 0 to indicate that the length of a NULL string is 0.
• Iterates through the string, incrementing the counter i for each character until the null terminator (\0) is reached.
• Returns the value of i, which represents the total length of the string.

ft_strncat

The ft_strncat function concatenates a specified number of characters from the buffer string to the end of the saved string. It dynamically allocates memory for the concatenated result and updates the saved pointer to point to the new string.

int	ft_strncat(char **saved, char *buffer, int size)
{
	int		i;
	int		j;
	char	*str;

	i = 0;
	if (!(*saved))
		str = malloc((size + 1) * sizeof(char));
	else
		str = malloc(((ft_strlen(*saved) + size) + 1) * sizeof(char));
	if (!str)
		return (0);
	while (*saved && (*saved)[i])
	{
		str[i] = (*saved)[i];
		i++;
	}
	j = 0;
	while (j < size)
		str[i++] = buffer[j++];
	str[i] = '\0';
	if (*saved)
		free(*saved);
	*saved = NULL;
	*saved = str;
	return (1);
}

Parameters:

• char **saved: A double pointer to the string that will be extended with the content from the buffer.
• char *buffer: A pointer to the string from which characters will be appended to saved.
• int size: The number of characters from the buffer to append to saved.

Functionality:

• Initializes integer variables i and j to 0 for indexing.
• Allocates memory for the new concatenated string. If saved is NULL, it allocates enough space for size + 1 characters. If saved is not NULL, it allocates enough space for the combined length of saved and the new size characters plus the null terminator.
• Returns 0 if memory allocation fails.
• Copies the content of saved to the newly allocated string str.
• Appends size characters from buffer to the end of str.
• Adds a null terminator to str.
• Frees the memory previously allocated to saved if it was not NULL.
• Updates saved to point to the newly concatenated string str.
• Returns 1 to indicate successful concatenation.

ft_strtrim_jump

The ft_strtrim_jump function extracts a substring from the beginning of saved up to and including the first newline character (\n). It then updates saved to contain only the remaining part of the original string after the newline character. The extracted substring is returned, while the original string is modified.

char	*ft_strtrim_jump(char **saved)
{
	char	*strcut;
	char	*strsaved;
	int		i;
	int		j;

	i = -1;
	strcut = malloc((ft_isnewline(*saved) + 2) * sizeof(char));
	if (!strcut)
		return (NULL);
	while ((*saved)[++i] != '\n')
		strcut[i] = (*saved)[i];
	strcut[i++] = '\n';
	strcut[i] = '\0';
	strsaved = NULL;
	if ((*saved)[i])
	{
		j = 0;
		strsaved = malloc((ft_strlen(&(*saved)[i]) + 1) * sizeof(char));
		while ((*saved)[i])
			strsaved[j++] = (*saved)[i++];
		strsaved[j] = '\0';
	}
	free(*saved);
	*saved = strsaved;
	return (strcut);
}

Parameters:

• char **saved: A double pointer to the string from which the function will extract and remove the substring up to the first newline character.

Functionality:

• Allocates memory for strcut, which will store the substring from the start of saved up to and including the first newline character (\n).
• Returns NULL if memory allocation for strcut fails.
• Copies characters from saved to strcut until the newline character is encountered.
• Appends the newline character (\n) to strcut, followed by a null terminator (\0).
• Allocates memory for strsaved to store the remaining part of saved after the newline character. If there are no characters left after the newline, strsaved is set to NULL.
• Copies the remaining characters from saved to strsaved.
• Frees the memory previously allocated to saved and updates saved to point to strsaved.
• Returns strcut, which contains the substring up to and including the first newline character.

Get_next_line.c

get_last_line

The get_last_line function extracts the entire string stored in saved, returning it as a new string. After extracting the string, it frees the memory associated with saved and sets saved to NULL.

char	*get_last_line(char **saved)
{
	char	*res;
	int		i;

	if (!(*saved) || !(*saved)[0])
		return (NULL);
	res = malloc(sizeof(char) * (ft_strlen(*saved) + 1));
	if (!res)
		return (NULL);
	i = 0;
	while ((*saved)[i] != '\0')
	{
		res[i] = (*saved)[i];
		i++;
	}
	res[i] = '\0';
	free(*saved);
	*saved = NULL;
	return (res);
}

Parameters:

• char **saved: A double pointer to the string that will be extracted and freed.

Functionality:

• Checks if saved is NULL or if it points to an empty string. If either is true, the function returns NULL.
• Allocates memory for res, a new string that will store the contents of saved.
• Returns NULL if memory allocation for res fails.
• Copies each character from saved to res until the end of the string (\0) is reached.
• Appends a null terminator (\0) to res to ensure it is a properly terminated string.
• Frees the memory previously allocated to saved and sets saved to NULL.
• Returns the new string res, which contains the entire original content of saved.

ft_readfd

The ft_readfd function reads data from a file descriptor fd into the saved string until a newline character (\n) is found or the end of the file is reached. The function returns a string up to the newline character or the remaining content of the file if no newline is found.

char	*ft_readfd(char **saved, int fd)
{
	int		readed;
	char	*buffer;

	while (ft_isnewline((*saved)) == -1)
	{
		buffer = malloc(BUFFER_SIZE * sizeof(char));
		if (!buffer)
			return (NULL);
		readed = read(fd, buffer, BUFFER_SIZE);
		if (readed > 0)
			readed = ft_strncat(saved, buffer, readed);
		free(buffer);
		if (readed == 0)
			return (get_last_line(saved));
		else if (readed == -1)
		{
			if ((*saved))
			{
				free((*saved));
				(*saved) = NULL;
			}
			return (NULL);
		}
	}
	return (ft_strtrim_jump(saved));
}

Parameters:

• char **saved: A double pointer to the string that stores the accumulated content read from the file descriptor.
• int fd: The file descriptor from which data is read.

Functionality:

• Continuously reads from the file descriptor fd into saved until a newline character (\n) is encountered in saved.
• Allocates memory for buffer to temporarily hold the data read from the file.
• Returns NULL if memory allocation for buffer fails.
• Calls the read function to read up to BUFFER_SIZE bytes from fd into buffer.
• If data is successfully read (readed > 0), it appends the data in buffer to saved using ft_strncat.
• Frees the memory allocated for buffer after each read operation.
• If readed == 0, indicating that the end of the file is reached, it returns the remaining content of saved by calling get_last_line.
• If an error occurs during reading (readed == -1), it frees saved, sets it to NULL, and returns NULL.
• If a newline character is found, it returns the content of saved up to and including the newline character by calling ft_strtrim_jump.

get_next_line

The get_next_line function reads and returns the next line from a file descriptor fd, including the newline character (\n) if present. It handles multiple file descriptors simultaneously by using a static array to keep track of the saved state for each file descriptor.

char	*get_next_line(int fd)
{
	static char	*saved[1024];

	if (fd < 0 || fd >= 1024 || BUFFER_SIZE <= 0)
		return (NULL);
	if (saved[fd] && ft_isnewline(saved[fd]) > -1)
		return (ft_strtrim_jump(&saved[fd]));
	else
		return (ft_readfd(&saved[fd], fd));
	return (NULL);
}

Parameters:

• int fd: The file descriptor from which the next line is to be read.

Functionality:

• Uses a static array saved[1024] to store the accumulated data for each file descriptor up to 1024.
• Checks if the fd is valid (i.e., non-negative, less than 1024, and the BUFFER_SIZE is greater than 0). If any of these conditions are not met, the function returns NULL.
• If there is already data saved for the given fd and a newline character is present in that data, it extracts and returns the next line using ft_strtrim_jump.
• If no newline character is found in the saved data, or if the saved data is NULL, the function calls ft_readfd to read more data from the file descriptor until a newline is found or the end of the file is reached.
• The function ultimately returns either the next line from the file descriptor or NULL if an error occurs or no more lines are available.