title: Can't use CTRL-<Space> with Cscope plugin in gvim (windows)
body: <p><strong>Configuration</strong> </p>
  
  <ul>
  <li>Windows 7 Service Pack 1 (64-bit)</li>
  <li>VIM 7.4 (2013 Aug 10), 32-Bit GUI version</li>
  <li>cscope_macros.vim plugin from www.vim.org, version 2.0.0</li>
  </ul>
  
  <p><strong>The problem</strong></p>
  
  <p>The plugin maps several cscope find functions to open in horizontal or vertical splits using 'CTRL-spacebar' or <code>&lt;CTRL-@&gt;</code>, as this is how VIM recognises it according to the plugin documentation. here is a  snippet from the plugin:</p>
  
  <pre><code>" Using 'CTRL-spacebar' (intepreted as CTRL-@ by vim) then a search type
  " makes the vim window split horizontally, with search result displayed in
  " the new window.
  "
  " (Note: earlier versions of vim may not have the :scs command, but it
  " can be simulated roughly via:
  "    nmap &lt;C-@&gt;s &lt;C-W&gt;&lt;C-S&gt; :cs find s &lt;C-R&gt;=expand("&lt;cword&gt;")&lt;CR&gt;&lt;CR&gt;  
  
  nmap &lt;C-@&gt;s :scs find s &lt;C-R&gt;=expand("&lt;cword&gt;")&lt;CR&gt;&lt;CR&gt; 
  nmap &lt;C-@&gt;g :scs find g &lt;C-R&gt;=expand("&lt;cword&gt;")&lt;CR&gt;&lt;CR&gt; 
  </code></pre>
  
  <p>However, 'CTRL-spacebar' does not work. When I look at what has been mapped <code>&lt;C-@&gt;</code> is actually translated as <code>&lt;nul&gt;</code>. For example, if I use the command <code>:map</code>, this is the result for the cscope plugin mapped keys.</p>
  
  <pre><code>n   &lt;nul&gt;d        :scs find d &lt;C-R&gt;=expand("&lt;cword&gt;")&lt;CR&gt;&lt;CR&gt;&lt;Tab&gt;
  n   &lt;nul&gt;i        :scs find i &lt;C-R&gt;=expand("&lt;cfile&gt;")&lt;CR&gt;&lt;CR&gt;&lt;Tab&gt;
  n   &lt;nul&gt;f        :scs find f &lt;C-R&gt;=expand("&lt;cfile&gt;")&lt;CR&gt;&lt;CR&gt;&lt;Tab&gt;
  n   &lt;nul&gt;e        :scs find e &lt;C-R&gt;=expand("&lt;cword&gt;")&lt;CR&gt;&lt;CR&gt;&lt;Tab&gt;
  </code></pre>
  
  <p>The only thing I can find 'CTRL-spacebar'/<code>&lt;CTRL-@&gt;</code> (<code>:help index</code>) is</p>
  
  <pre><code>tag     char        action in Insert mode   ~
  -----------------------------------------------------------------------
  i_CTRL-@    CTRL-@      insert previously inserted text and stop
                          insert
  </code></pre>
  
  <p>But this is not the behaviour I observe. </p>
  
  <p>When I try using 'CTRL-spacebar' in insert mode all that happens is that a space is inserted at the cursor. When I use it in normal mode it seems to move the cursor to the beginning of the next word, or the next line if it is blank.</p>
  
  <p>So, how do I map 'CTRL-spacebar' in VIM on windows?</p>