char ch[0] 과 char *ch

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

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

c표준은 아니고 gcc extensioin이라는데,
http://gcc.gnu.org/onlinedocs/gcc-4.0.2/gcc/Zero-Length.html#Zero-Length