title: How current_acc is modified in pjsip?
body: <p>When I take a look into iOS Application which uses pjsip I found it. reg_acc_id is define as -1. 
  <code>pjsua_acc_id reg_acc_id = -1;</code> 
  And this reg_acc_id is used to register the user.
  <code>pjsua_acc_add(&amp;acc_cfg, PJ_TRUE, &amp;reg_acc_id);</code></p>
  
  <pre><code>// To Check registration is successful or not
  if (status != PJ_SUCCESS) {
        pjsua_perror(THIS_FILE, "Error adding new account", status);
    }
  
    printf("\nREGISTRATION ACCOUNT ID IS :::: %d\n",reg_acc_id);
    pjsua_acc_set_default(reg_acc_id);
  </code></pre>
  
  <p><code>REGISTRATION ACCOUNT ID IS :::: %d\n",reg_acc_id</code> this line prints "2".... I wonder How? How registration account is incremented by default? What Background process is performed?Any one please clarify my doubts.Thanks in advance.</p>