size

static VALUE
rb_file_size(VALUE obj)
{
    rb_io_t *fptr;
    struct stat st;

    GetOpenFile(obj, fptr);
    if (fptr->mode & FMODE_WRITABLE) {
        rb_io_flush(obj);
    }
    if (fstat(fptr->fd, &st) == -1) {
        rb_sys_fail_path(fptr->pathv);
    }
    return OFFT2NUM(st.st_size);
}