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Arrays of Length Zero

6.17 Arrays of Length Zero

Zero-length arrays are allowed in GNU C. They are very useful as the last element of a structure that 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 ISO C90, you would have to give contents a length of 1, which means either you waste space or complicate the argument to malloc.

In ISO C99, you would use a flexible array member, which is slightly different in syntax and semantics:

  • Flexible array members are written as contents[] without the 0.
  • Flexible array members have incomplete type, and so the sizeof operator may not be applied. As a quirk of the original implementation of zero-length arrays, si