title: Matching a whole string with case insensitive
body: <p>I'm looking for a function if available to match a whole word for example:</p>
  
  <pre><code>std::string str1 = "I'm using firefox browser";
  std::string str2 = "The quick brown fox.";
  std::string str3 = "The quick brown fox jumps over the lazy dog.";
  </code></pre>
  
  <p>Only <code>str2</code> and <code>str3</code> should match for the word <code>fox</code>. So, it doesn't matter if there is a symbol like period (.) or a comma (,) before or after the word and it should match and it also has to be case-insensitive search at the same time.</p>
  
  <p>I've found many ways to search a case insensitive string but I would like to know something for matching a whole word.</p>