CODEWITHSUNDEEP
clinuxkernel
c0de
c0de

Reputation: 1172

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

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?

Upvotes: 73

Views: 20209

Answers (2)

Reed Copsey
Reed Copsey

Reputation: 564891

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 };

Upvotes: 59

sidyll
sidyll

Reputation: 59327

It's sometimes called "designated initialization". This is a C99 addition, though it's been a GNU extension for a while.

In the list, each . names a member of the struct to initialize, the so called designator.

Upvotes: 14

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