title: what is alloc.h?
body: <p>what is <code>alloc.h</code>? some questions on SO like <a href="https://stackoverflow.com/q/7006256/1526667">this</a> and <a href="https://stackoverflow.com/q/4395415/1526667">this</a> have included <code>alloc.h</code>. </p>
  
  <p>but, <a href="http://ideone.com/o35Hr" rel="nofollow noreferrer">when  i tried to include it gcc gives error </a> as <code>error: alloc.h: No such file or directory</code></p>
  
  <p>Has such file ever existed or those questions have included it just by mistake?</p>