title: compare with a 6-byte long string of zeros
body: <p>in my code I work with Ethernet MAC addresses and need to compare for a 00:00:00:00:00:00 address; the easiest solution I came up with is this:</p>
  
  <pre><code>#define ETH_ADDR_LEN  6
  unsigned char mac[ETH_ADDR_LEN] = { 0x1, 0x2, 0x3, 0x4, 0x5, 0x6 };  /* example */
  const unsigned char empty[ETH_ADDR_LEN] = { 0, };
  
  if (memcmp(mac, empty, ETH_ADDR_LEN) == 0) {
    ....
  }
  </code></pre>
  
  <p>Is there a more concise way to achieve my goal?
  Simply memcmp(mac, "", 6) won't work -- may I know why?</p>
  
  <p>Thanks in advance!</p>