title: Is stringstream better than string's operator '+' for string objects concatenation?
body: <p>For example, I have two string objects:string str_1, str_2. I want to concatenate to them. I can use two methods:
  method 1:</p>
  
  <pre><code>std::stringstream ss;
  //std::string str_1("hello");
  //std::string str_2("world");
  ss &lt;&lt; "hello"&lt;&lt; "world"；
  const std::string dst_str = std::move(ss.str());
  </code></pre>
  
  <p>method 2:</p>
  
  <pre><code>std::string str_1("hello");
  std::string str_2("world");
  const std::string dst_str = str_1 + str_2;
  </code></pre>
  
  <p>Because the string's buffer is read only, when you change the string object, its buffer will destroy and create a new one to store new content. So method 1 is better than method 2? Is my understanding correct? </p>