title: Is it possible to define some macro into the header file using some project settings or makefile options?
body: <p>Is it possible to add a <code>#define _MYDEFINE_</code> in my header file based on some options in the project settings. For Ex: Suppose in my exposed header file (which is delivered along with the library) I have some macros like shown below:</p>
  
  <pre><code>#ifdef _MYDEFINE_
  #define ABC 2
  #else
  #define ABC 4
  #endif
  </code></pre>
  
  <p>Now, while building my library, I can add <code>_MYDEFINE_</code> in my settings, but I don't want the user of the library to add <code>_MYDEFINE_</code> in his project settings or code. Instead I want "<code>#define _MYDEFINE_</code>" to automatically get added in the beginning of the header. </p>
  
  <p><strong>Note:</strong> <code>#define _MYDEFINE_</code> should get added only when it is defined in my preprocessor settings. For other settings it should not get added.</p>
  
  <p>If not possible through project settings, are there any innovative ways of getting it done?
  Any ideas are welcome.</p>