title: Definition of int64_t
body: <p>I am new to C/C++, so I have a couple of questions about a basic type: </p>
  
  <p>a) Can you explain to me the difference between <code>int64_t</code> and <code>long</code> (<code>long int</code>)? 
  In my understanding, both are 64 bit integers. Is there any reason to choose one over the other?</p>
  
  <p>b) I tried to look up the definition of <code>int64_t</code> on the web, without much success. Is there an authoritative source I need to consult for such questions?</p>
  
  <p>c) For code using <code>int64_t</code> to compile, I am currently including <code>&lt;iostream&gt;</code>, which doesn't make much sense to me. Are there other includes that provide a declaration of <code>int64_t</code>?</p>