title: Xcode 7: Set Preprocessor Macros per architecture
body: <p>I need to set <code>Preprocessor Macro</code> in <code>Xcode</code> just for specific architecture (arm64). How can I do this? </p>
  
  <p>There is similar question here on Stackoverflow: <a href="https://stackoverflow.com/questions/28665402/xcode-6-set-preprocessor-macros-per-architecture">Xcode 6: Set Preprocessor Macros per architecture</a>. 
  But in my case <code>Xcode 7</code> just doesn’t let me to choose the architecture. Tried on <code>Xcode</code> versions <code>7.1.1</code> and <code>7.3.1</code> with the same result: the only architecture option offered by Xcode is “*” (see the picture below).
  <a href="https://i.stack.imgur.com/pH1OA.png" rel="nofollow noreferrer">Preprocessor settings section</a></p>
  
  <p>Just in case here are my Architectures settings:
  <a href="https://i.stack.imgur.com/IHRcd.png" rel="nofollow noreferrer">Architectures settings section</a></p>
  
  <p>To give you more understanding why do I actually need this: 
  I use 3rd-party C-library which relies on a flag set to tell it if it is running on a 32-bit or 64-bit platform.
  Note from library's integration guide: “When building for the 64-bit architecture, the <code>_64BIT</code> macro must be added in the pre-processor macro section of Xcode.”</p>
  
  <p>So here is what I've tried:</p>
  
  <ul>
  <li>to find a way to set architecture-specific macro in Xcode UI (described above)</li>
  <li>to amend <code>.pbxproj</code> file manually by replacing <code>GCC_PREPROCESSOR_DEFINITIONS</code>[arch=*] with <code>GCC_PREPROCESSOR_DEFINITIONS</code>[arch=arm64] (didn’t give desired effect)</li>
  </ul>
  
  <p>Do you have any ideas what is wrong with my <code>Xcode</code> settings, why doesn’t it show architecture options in <code>Preprocessor</code> section? Or are there other ways to configure macro in my case?</p>