title: Apple Mach-O Linker Error -- Undefined symbols for architecture arm64
body: <p>I am getting a Apple Mach-O Linker Error every time I run my project, I'm trying to build using iPhone 6s with iOS 10.0.</p>
  
  <p>Undefined symbols for architecture <code>arm64</code>:</p>
  
  <pre><code>"boost::gregorian::greg_month::as_short_string() const", referenced from:
        boost::date_time::month_formatter&lt;boost::gregorian::greg_month, boost::date_time::iso_format&lt;char&gt;, char&gt;::format_month(boost::gregorian::greg_month const&amp;, std::__1::basic_ostream&lt;char, std::__1::char_traits&lt;char&gt; &gt;&amp;) in libSHP.a(Timer.o)
  
  ld: symbol(s) not found for architecture arm64
  
  clang: error: linker command failed with exit code 1 (use -v to see invocation)
  </code></pre>
  
  <p>I'm using Xcode version 8.1 </p>