title: ROS: subscribe function does not recognize my callback method
body: <p>I am receiving this error "error: no matching function for call to <code>‘ros::NodeHandle::subscribe(const char [24], int, &lt;unresolved overloaded function type&gt;)’</code></p>
  
  <p>This is my call back function in my class BangBangControlUnit</p>
  
  <p><code>// on message reciept: 'current_maintained_temp'
      void current_maintained_temp_callback(const std_msgs::Int32::ConstPtr&amp; msg){
        temp_to_maintain = msg-&gt;data;<br>
      }</code></p>
  
  <p>and this is how i am using subscribe in my main function </p>
  
  <p><code>// subscribe to 'current_maintained_temp'
    ros::Subscriber current_maintained_temp_sub = n.subscribe("current_maintained_temp", 1000, control.current_maintained_temp_callback);</code></p>
  
  <p>can someone tell me what i did wrong?</p>