title: VIM - Sourcing tags from multiple locations in project
body: <p>Good day,</p>
  
  <p>I typically work on relatively small (less than 20,000 lines of code) projects that are all self contained within a single directory, have their own Makefile, and are fairly easy to work with.</p>
  
  <p>VIM is my preferred editor, and when I open a project, I typically build the ctags list via a mapping to the <kbd>F10</kbd> key:</p>
  
  <pre><code>map &lt;F10&gt; :!ctags -R --c++-kinds=+p --fields=+iaS --extra=+q .&lt;CR&gt;
  </code></pre>
  
  <p>This allows me to jump to the definition of a variable/struct/etc via moving the cursor over the text, and hitting <kbd>CTRL</kbd>+<kbd>]</kbd>, as well as using code completion with a drop-down list via OmniCppComplete.</p>
  
  <p>However, I am now working on a slightly larger project which makes use of LOTS of structures. Furthermore, many of these structures have arrays of other custom structures as members, so code completion is a very useful and important tool for me right now.</p>
  
  <p>I have two paths that include a lot of <code>.C</code> files and <code>.h</code> files, and they may change from machine to machine. On each machine, however, we have an environment variable in our <code>.bashrc</code> file that points to them like so:</p>
  
  <pre><code>SDK_SRC_PLUS_HEADERS=/public/sdk
  THIRD_PARTY_SDK=/private/sdk
  </code></pre>
  
  <p>I would like to be able to have VIM automatically refer to the contents of these additional paths when I attempt to do code completion (via VIM's built-in OmniCppComplete feature), or to jump to the files in these locations when I use <kbd>CTRL</kbd>+<kbd>]</kbd> in VIM to jump to the definition of a struct, function, variable, etc.</p>
  
  <p>So, for both of the above paths, I <code>cd</code> into them, and generate the tags via <code>ctags -R</code>. Then, I modified my <code>~/.vimrc</code> file to include additional tags paths, like so:</p>
  
  <pre><code>tags=./tags
  tags+=$SDK_SRC_PLUS_HEADERS/tags
  tags+=$THIRD_PARTY_SDK/tags
  </code></pre>
  
  <p>I then <code>cd</code> into my project at <code>/home/user1/projects/test</code>, start VIM, and hit <kbd>F10</kbd> in VIM to index it. However, this does not work at all. In fact, it breaks my ability to even use tags just for the project itself (ie: <kbd>CTRL</kbd>+<kbd>]</kbd> now does nothing). </p>
  
  <p>Does anyone have any suggestions on how I could have code completion source tags and jump-to-definitions using multiple source directories via environment variables?</p>
  
  <p>Thank you all in advance for your time and assistance!</p>