title: Ensures() - guideline support library
body: <p>I am trying to understand how to use <code>Ensures()</code> in code. As given in the <a href="https://github.com/isocpp/CppCoreGuidelines/blob/master/CppCoreGuidelines.md#i8-prefer-ensures-for-expressing-postconditions" rel="noreferrer">example</a>, if I tried using <code>Ensures()</code> as follows...</p>
  
  <pre><code>int main(void)
  {
      int result = 0;
      // Some calculation
      Ensures(result == 255);
      return 0;
  }
  </code></pre>
  
  <p>If the <code>result</code> variable is not equal to <code>255</code>, the program crashes with the following output <code>"terminate called without an active exception"</code>. My question is how to use <code>Ensures()</code> properly? </p>