title: C++ how to create a 'global' library
body: <p>I'm working on a project that has the line: <code>#include &lt;fftw3.h&gt;</code></p>
  
  <p>Now I can simply download and make <a href="http://fftw.org" rel="nofollow">fftw</a>. But how do I make it a 'global' library?</p>
  
  <p>I have tried adding it to <code>$PKG_CONFIG_PATH</code> but this doesn't seem to work. I'm constantly ending up with this error: <code>main.c:30:10: fatal error: 'fftw3.h' file not found</code></p>
  
  <p>So my question is: where do I need to make the fftw library (or any library for that matter) to make it globally accessible?</p>
  
  <p><em>note: I might use the term global incorrectly, in that case, please let me know what the correct term would be.</em></p>
  
  <p><strong>Update:</strong> The command is:</p>
  
  <pre><code>gcc -Wall -march=native -O3 -ffast-math `pkg-config --cflags fftw3` `pkg-config --cflags sndfile` -c -o main.o main.c
  </code></pre>
  
  <p><code>main.c</code> contains the line</p>
  
  <pre><code>#include &lt;fftw3.h&gt;
  </code></pre>