title: Join const char* in a string
body: <p>I am trying to put <code>const char*</code> variables in a string with concatenate, these are just initialising variables. Here is how I am trying to do that in <code>String input</code>: </p>
  
  <pre><code>const char* topic1 = "home/bathroomlight";
  const char* topic2 = "home/bathroomfan";
  const char* topic3 = "home/dressingroomlight";
  const char* topic4 = "home/makeuplight";
  
  const char* topic1_status = "home/bathroomlight/status";
  const char* topic2_status = "home/bathroomfan/status";
  const char* topic3_status = "home/dressingroomlight/status";
  const char* topic4_status = "home/makeuplight/status";
  
  String input = "{ \"Bath Room Light\" : { \"pin\" : 1, \"status\" : \"off\", \"type\" : \"light\", \"command_topic\" : "+  topic1 +", \"state_topic\" : "+topic1_status +" }, \"Bathroom Fan\" : { \"pin\" : 2, \"status\" : \"off\", \"type\" : \"fan\", \"command_topic\" : "+topic2+", \"state_topic\" : "+topic2_status+" }, \"Dressing Room Light\" : { \"pin\" : 4, \"status\" : \"off\", \"type\" : \"light\", , \"command_topic\" : "+ topic3 +", \"state_topic\" : "+ topic3_status +" }, \"Makeup Light\" : { \"pin\" : 3, \"status\" : \"off\", \"type\" : \"light\", \"command_topic\" : "+ topic4 +", \"state_topic\" : "+ topic4_status +" } }";
  </code></pre>
  
  <p>When I am trying to append these values to <code>input</code> String. Its not allowing me. As I guess the above value is in <code>const char*</code> how can I add that? any suggestions will be helpful. </p>