title: how to convert hex string to unsigned 64bit (uint64_t) integer in a fast and safe way?
body: <p>I tried </p>
  
  <pre><code>sscanf(str, "%016llX", &amp;int64 );
  </code></pre>
  
  <p>but seems not safe. Is there a fast and safe way to do the type casting?</p>
  
  <p>Thanks~</p>