title: Eclipse can't find header filers even though include paths have been set
body: <p>When creating a new C project in a particular Eclipse environment which uses GCC, I run into a peculiar linker problem:</p>
  
  <blockquote>
    <p>Fatal error: my_header.h: No such file or directory.</p>
  </blockquote>
  
  <p>I get this problem since "my_header.h" resides in a sub folder. After investigation, I found out that you need to include sub folders in the GCC include path (option <code>-I</code>). How this is done seems to vary between different Eclipse implementations, but it should be something like </p>
  
  <p>Project -> Properties -> C/C++ Build -> Settings -> Compiler -> Includes</p>
  
  <p>Where "compiler" may have a different name in different implementations, and "includes" may be called "input" or similar. </p>
  
  <p>There should be an option to add the include path (option <code>-I</code>) where you can set the path relative to the specific project, by clicking an "Add" icon followed by Workspace button, then select the directory. Eclipse then generates a path, which should look something like </p>
  
  <p><code>"${workspace_loc:/${ProjName}/app}"</code></p>
  
  <p>Do this for all sub folders in the project (and their sub folders).</p>
  
  <p>But despite doing the above for the relevant folder, I still get the "no such file or directory" error. What could be the problem?</p>
  
  <hr>
  
  <p>(I'm posting this Q&amp;A style since I want to share the solution of this problem with others)</p>