title: How to check if constant is used in project
body: <p>I have a big project with many Objective C and Swift files.
  There's a Constants.h file which contains many constants with #define. It looks like this:</p>
  
  <pre><code>#define kConstant1  @"constant1"
  #define kConstant2  @"constant2"
  #define kConstant3  @"constant3"
  #define kConstant4  @"constant4"
  ...
  </code></pre>
  
  <p>In the project there are many files (Swift and Objective C) which use these constants. Unfortunately there are also constants which aren't used by any file in the code, so they are unused variables. I want to find out which constants are used and which are not, to delete the constants which aren't used. There are about 3000 constants in this file so it would take too long to search through the code manually for each constant.</p>
  
  <p>Is there any other way to find out which #define variable is used by the code?</p>