title: Where is boost::filesystem::last_write_time?
body: <p>This is the linker error I'm getting.  All the rest of my boost::filesystem things are resolving.  I'm not understanding why this one does not.  I thought it was a problem with boost 1.40, so I upgraded to 1.44 and the problem remains.  I'm using <code>#define BOOST_FILESYSTEM_VERSION 3</code> but I see no mention of last_write_time not being provided in that case.  It seems the underlying implementation is missing, even though the api portion is present.</p>
  
  <pre><code>1&gt;TestPruner.obj : error LNK2019: unresolved external symbol "void __cdecl boost::filesystem3::detail::last_write_time(class boost::filesystem3::path const &amp;,long,class boost::system::error_code *)" (?last_write_time@detail@filesystem3@boost@@YAXABVpath@23@JPAVerror_code@system@3@@Z) referenced in function "void __cdecl boost::filesystem3::last_write_time(class boost::filesystem3::path const &amp;,long)" (?last_write_time@filesystem3@boost@@YAXABVpath@12@J@Z)
  </code></pre>
  
  <p>Oh yea, using Windows VS2008.</p>
  
  <p>The code involved is:</p>
  
  <pre><code>time_t curTime = time(NULL);
  bfs::last_write_time(bfs::path("TestData/PruneTest/completed/Batch001.DAT"), curTime);
  </code></pre>
  
  <p>Anyone else run into this?</p>
  
  <p>And it happens with <code>#define BOOST_FILESYSTEM_VERSION 2</code> as well.  The Boost libraries I'm using are from boostpro (prebuilt, yea, I'm lazy)</p>
  
  <pre><code>2&gt;TestPruner.obj : error LNK2019: unresolved external symbol "class boost::system::error_code __cdecl boost::filesystem2::detail::last_write_time_api(class std::basic_string&lt;char,struct std::char_traits&lt;char&gt;,class std::allocator&lt;char&gt; &gt; const &amp;,long)" (?last_write_time_api@detail@filesystem2@boost@@YA?AVerror_code@system@3@ABV?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@J@Z) referenced in function "void __cdecl boost::filesystem2::last_write_time&lt;class boost::filesystem2::basic_path&lt;class std::basic_string&lt;char,struct std::char_traits&lt;char&gt;,class std::allocator&lt;char&gt; &gt;,struct boost::filesystem2::path_traits&gt; &gt;(class boost::filesystem2::basic_path&lt;class std::basic_string&lt;char,struct std::char_traits&lt;char&gt;,class std::allocator&lt;char&gt; &gt;,struct boost::filesystem2::path_traits&gt; const &amp;,long)" (??$last_write_time@V?$basic_path@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@Upath_traits@filesystem2@boost@@@filesystem2@boost@@@filesystem2@boost@@YAXABV?$basic_path@V?$basic_string@DU?$char_traits@D@std@@V?$allocator@D@2@@std@@Upath_traits@filesystem2@boost@@@01@J@Z)
  </code></pre>
  
  <p>From /versbose:lib</p>
  
  <pre><code>Searching e:\Program Files\boost\boost_1_44\lib\libboost_thread-vc90-mt-gd-1_44.lib:
  Searching e:\Program Files\boost\boost_1_44\lib\libboost_date_time-vc90-mt-gd-1_44.lib:
  </code></pre>