title: constexpr string vs const string
body: <p>We are migrating some of our code from c++03 to c++14 and wherever there is some performance gain we want to use c++14 features.Now in one of our projects we are parsing csv based on column names and these column names are declared in one header file like this :</p>
  
  <pre><code>const string ITEM_NAME = "Item Name";
  const string ITEM_ID = "Item Id";
  </code></pre>
  
  <p>There are hundred of constants like this so what I want to know is Is there any significant performace gain if i change above code to something like this :</p>
  
  <pre><code>constexpr string ITEM_NAME = "Item Name";
  constexpr string ITEM_ID = "Item Id";
  </code></pre>
  
  <p>Also is there any limit on number of constexpr that we can have in our binary since they need to be stored in read only memory ?</p>
  
  <p>Does compiler automatically optimize old c++03 code also and place const variables also in read only memory and this effort is not worth ?</p>