title: Gtk3 - unresolved inclusion
body: <p>I am using Ubuntu 18.04.4, and Eclipse 2019-12 (4.14.0) and I try to create a little C application with the help of Glade for the user interface.</p>
  
  <p>Adding the following header files in C results in "unresolved inclusion" error:</p>
  
  <pre><code>#include &lt;gtk/gtk.h&gt;
  #include &lt;gtk/gtkx.h&gt;
  </code></pre>
  
  <p>I have searched and tried in many ways to fix this, but unfortunately I didn't manage (I am new to linux/eclipse). The most easy solution seems to be a package called "Pkg-config" that knows itself how to add the gtk package, but unfortunately, this version of Eclipse does not support it.</p>
  
  <p>The compiler sends the following error:</p>
  
  <pre><code>10:22:19 **** Incremental Build of configuration Debug for project MyTestProject ****
  
  make all 
  Building file: ../src/MyTestProject.c
  Invoking: GCC C Compiler
  gcc -O0 -g3 -Wall -c -fmessage-length=0 -MMD -MP -MF"src/MyTestProject.d" -MT"src/MyTestProject.o" -o "src/MyTestProject.o" "../src/MyTestProject.c"
  ../src/MyTestProject.c:17:10: fatal error: gtk/gtk.h: No such file or directory
   #include &lt;gtk/gtk.h&gt;
            ^~~~~~~~~~~
  compilation terminated.
  src/subdir.mk:18: recipe for target 'src/MyTestProject.o' failed
  make: *** [src/MyTestProject.o] Error 1
  "make all" terminated with exit code 2. Build might be incomplete.
  
  10:22:19 Build Failed. 3 errors, 0 warnings. (took 466ms)
  </code></pre>
  
  <p>Any ideas how I can solve this? I mention that libgtk-3-dev is installed on my system and it appears inside the "includes" folder.</p>