title: Check if pair is empty or uninitialized
body: <pre><code> int main() {
  
     pair&lt;int, int&gt; res;
     // check here pair is empty ?
     // res = make_pair(1 , 2);
  
  
     return 0;
  }
  </code></pre>
  
  <p>In the above snippet what is the ideal way to check if a pair has been initilaized or not?</p>
  
  <p>EDIT: As pointed out in some answers below, using the word "uninitialized" is wrong here, to be more specific how do I check if the value has been explicitly set (other than the default constructor)</p>