title: String length of a NULL
body: <p>I was trying to find the string length of a <code>NULL</code> and <code>""</code></p>
  
  <p>when I tried <code>a=strlen("");</code> I got zero as output.
  and when I tried <code>a=strlen(NULL);</code> I got core dump error. </p>
  
  <p>What exactly happening in these two statements? Will memory allocate for <code>""</code></p>