title: c++ unordered_map compiling issue with g++
body: <p>I am using g++ in Ubuntu</p>
  
  <blockquote>
    <p>g++ (Ubuntu 4.4.3-4ubuntu5) 4.4.3</p>
  </blockquote>
  
  <p>I have this code </p>
  
  <pre><code>#include&lt;unordered_map&gt;
  using namespace std;
  
  bool ifunique(char *s){
    unordered_map&lt;char,bool&gt; h;
    if(s== NULL){
      return true;
    }
    while(*s){
      if(h.find(*s) != h.end()){
        return false;
      }
      h.insert(*s,true);
      s++;
    }
    return false;
  }
  </code></pre>
  
  <p>when I compile using </p>
  
  <pre><code>g++ mycode.cc
  </code></pre>
  
  <p>I got error</p>
  
  <pre><code> error: 'unordered_map' was not declared in this scope
  </code></pre>
  
  <p>Am I missing something?</p>