title: Static library gives strange errors on Xcode
body: <p>I made a static library(.a) following the instructions of  Ray Wenderlich, compiled it without errors and warnings, and then I included it on a new project.  When I tried to build the new project, I got this error:</p>
  
  <p><a href="https://i.stack.imgur.com/tI3qO.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/tI3qO.png" alt="error screenshot"></a></p>
  
  <pre><code>/Users/.../PruebaInsights/PruebaInsights/libInsightsLib.a:1:1: Source file is not valid UTF-8
  /Users/.../PruebaInsights/PruebaInsights/libInsightsLib.a:1:5: Null character ignored
  /Users/.../PruebaInsights/PruebaInsights/libInsightsLib.a:1:8: Expected identifier or '('
  /Users/.../PruebaInsights/PruebaInsights/libInsightsLib.a:2:3: Invalid filename for line marker directive
  /Users/.../PruebaInsights/PruebaInsights/libInsightsLib.a:3:10: Null character ignored
  </code></pre>
  
  <p>Why do I get these errors on the library, if I compiled correctly?</p>