4.13 Arrays of Length Zero

Zero-length arrays are allowed in GNU C. They are very useful as the last element of a structure which is really a header for a variable-length object:

struct line {
  int length;
  char contents[0];
};

{
  struct line *thisline = (struct line *)
    malloc (sizeof (struct line) + this_length);
  thisline->length = this_length;
}

In standard C, you would have to give contents a length of 1, which means either you waste space or complicate the argument to malloc.