This project has been created as part of the 42 curriculum by .

Get Next Line (GNL)

Description

Get Next Line is a core project of the 42 School curriculum.
The objective of this project is to implement a function, get_next_line, that reads a file descriptor line by line, returning one line per function call.

The function must:

• Read from a file descriptor until a newline character (\n) or End Of File (EOF) is reached.
• Preserve unread data between calls.
• Allocate memory dynamically for each returned line.
• Be robust against different buffer sizes and input sources.

The bonus part extends this behavior to support multiple file descriptors simultaneously, ensuring that reading from one file descriptor does not interfere with another.

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Function Prototype

char *get_next_line(int fd);

Returns a line ending with \n if present, or NULL if EOF is reached and no data remains or an error occurs.

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Instructions

Compilation for testing

get_next_line.c and get_next_line_bonus.c contain COMMENTED main funtions to test them. Uncomment them and compile the project with your own files or test files:

cc -Wall -Wextra -Werror get_next_line.c get_next_line_utils.c

For the bonus version:

cc -Wall -Wextra -Werror get_next_line_bonus.c get_next_line_utils_bonus.c

To test them just execute the a.out file with file name (or few file names if it is bonus) as arg to read them.

./a.out get_next_line.c

You may define BUFFER_SIZE at compile time:

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

Usage Example

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

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

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Algorithm & Design Choices

Core Algorithm

1. Buffered Reading

   • Use read() to fetch chunks of data of size BUFFER_SIZE.
   • If read() returned negative, it immidiatly skips the reading part, frees everything and returns NULL.
   • Else: append each chunk (stash_expand function) to a persistent buffer called the stash and repeat it until was_read == BUFFER_SIZE and buffer doesnt contain \n.

2. Line Extraction

   • If read() returned integer more then 0, it uses stach_extract_line is used to extract one line from stash and leave other chars in it. if it returned full stash, stash will be set to NULL.
   • If read() returned 0 (EOF) and the stash contains data, return the remaining data as the final line.
   • if it returned negative, it will just remove everything and return NULL

3. Memory Safety

   • All returned lines (or t_fd_list in bonus) are dynamically allocated.
   • All allocated memotry is freed when no longer needed.

Bonus

Bonus part works the same way, but it uses static t_fd_list with stashes and 3 additional methods instead of stash

typedef struct s_fd_list_node
{
    int                     fd;
    char                    *stash;
    struct s_fd_list_node   *next;
} t_fd_list;

Column 1	Column 2
add_node	Adds node with exact fd and returns it. If this node already exists, it will just return it
remove_node	Used to free the node by its fd
node_by_fd	Returns node with exact fd if it exists, otherwise NULL

This approach guarantees:

• No data loss between calls
• Minimal reads from the file descriptor
• Correct handling of partial lines

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Resources

Technical References

• man read
• man open
• man close
• 42 School subject PDF for get_next_line

AI Usage Disclosure

AI tools were used only for assistance, including:

• Finding errors
• Writing basic README

All implementation logic, coding, testing, and final decisions were made by the project author in compliance with 42 rules.

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