title: Boost and Autoconf
body: <p>I am making a project that uses Autoconf. I have the following in <code>configure.ac</code>:</p>
  
  <pre><code>AC_CHECK_HEADERS([boost/foreach.hpp], [],
      [AC_MSG_ERROR(You need the Boost libraries.)])
  </code></pre>
  
  <p>When I run <code>configure</code>, it says it cannot find this header file:</p>
  
  <pre><code>checking boost/foreach.hpp usability... no
  checking boost/foreach.hpp presence... no
  checking for boost/foreach.hpp... no
  configure: error: You need the Boost libraries.
  </code></pre>
  
  <p>This is strange, because I have Boost. If I remove the check, the code compiles, and I have Boost installed:</p>
  
  <pre><code>$ find /usr/include -name foreach.hpp
  /usr/include/boost/foreach.hpp
  /usr/include/boost/test/utils/foreach.hpp
  </code></pre>
  
  <p>Note that I did exactly the same with SDL, and it works.</p>
  
  <pre><code>AC_CHECK_HEADERS([SDL/SDL.h], [],
      [AC_MSG_ERROR(You need the SDL development library.)])
  </code></pre>
  
  <p>...</p>
  
  <pre><code>checking SDL/SDL.h usability... yes
  checking SDL/SDL.h presence... yes
  checking for SDL/SDL.h... yes
  </code></pre>