Objectives

int get_next_line(int fd, char **line)

• Calling the function in a loop will read the text available on a file descriptor one line at a time until EOF.
• Return 1 when a line has been read, 0 when EOF has been reached, -1 when an error happened.
• Able to manage multiple file descriptors.

What to know

Static variable

• Remains while the program is running.
• Is allocated memory in data segment

Difference between global and static variable is that static variable cannot be accessed from other files.

Why using static variable

• We need to call get_next_line until EOF, so we need a static variable to hold a line read with the amount of BUFFER_SIZE until the program ends.

File descriptor

• An abstract indicator used to access a file in Unix and related computer operating systems.
• Open returns file descriptor that are not allocated.
• 0 is for standard input, 1 is for standard output, 2 is for standard error.

Implementation

• get_next_line will read a file with the amount of BUFFER_SIZE and determine if the string is a line or not.
• If the string read is not a line, a function will read a file with same amount again.

static char *saved[OPEN_MAX]

• OPEN_MAX defined in <limits.h>, is the maximum number of files that one process can have open at any one time.
• Used double pointer to manage strings from n files.
• Will hold lines read until the program ends.

char buf[BUFFER_SIZE + 1]

• Temporary array that will hold a string read with the amount of BUFFER_SIZE.
• Will be joined with saved string.

Steps

1. Check if static variable saved[fd] includes new line.
   -> If yes, copy a string in saved[fd] until a new line to a given variable line.
   -> Then, saved[fd] will be overwritten into saved[fd] after a new line.
2. Read a file with the amount of BUFFER_SIZE.
   -> Join existing saved[fd] with buf.
   -> Return to step 1.

What to be careful

Memory leaks

• Malloc will be used in ft_strjoin and ft_strdup.
• saved[fd] will be overwritten with new memory allocation.
  -> Previous saved[fd] should be freed.

BUFFER_SIZE

• Since char buf[BUFFER_SIZE] is allocated in stack memory, if a function reads more than available stack size, it will cause stack overflow.
  -> Set as global or static variable that will be allocated in data segment.
  -> Allocate in heap memory using malloc.
  -> Manually increase stack memory size.