c - What does a dot before the variable name in struct mean?

Question

looking at the linux kernel source, I found this:

static struct tty_operations serial_ops = {
  .open = tiny_open,
  .close = tiny_close,
  .write = tiny_write,
  .write_room = tiny_write_room,
  .set_termios = tiny_set_termios,
};

I've never seen such a notation in C. Why is there a dot before the variable name?

Answer 1

This is a Designated Initializer, which is syntax added for C99. Relevant excerpt:

In a structure initializer, specify the name of a field to initialize with ‘.fieldname =’ before the element value. For example, given the following structure,

struct point { int x, y; }; 

the following initialization

struct point p = { .y = yvalue, .x = xvalue }; 

is equivalent to

struct point p = { xvalue, yvalue };