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  27 <a name="boost_tr1.implementation"></a><a class="link" href="implementation.html" title="Implementation">Implementation</a>
  28 </h2></div></div></div>
  29 <p>
  30       When Boost.TR1 is <a class="link" href="config.html" title="Configuration">configured</a> to make
  31       use of your standard library's native TR1 implementation, then it doesn't do
  32       very much: it just includes the appropriate header.
  33     </p>
  34 <p>
  35       When Boost.TR1 is using the Boost implementation of a particular component,
  36       then it includes the appropriate Boost header(s) and imports the necessary
  37       declarations in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span></code> with
  38       using declarations. Note that only those declarations that are part of the
  39       standard are imported: the implementation is deliberately quite strict about
  40       not including any Boost-specific extensions in <code class="computeroutput"><span class="keyword">namespace</span>
  41       <span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span></code>, in order to catch any portability errors
  42       in user code. If you really need to use Boost-specific extensions then you
  43       should include the Boost headers directly and use the declarations in <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">boost</span><span class="special">::</span></code> instead. Note that this style of implementation
  44       is not completely standards-conforming, in particular it is not possible to
  45       add user-defined template specializations of TR1 components into <code class="computeroutput"><span class="keyword">namespace</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">tr1</span></code>. There
  46       are also one or two Boost libraries that are not yet fully standards conforming,
  47       any such non-conformities are documented in <a class="link" href="subject_list.html" title="TR1 By Subject">the
  48       TR1 by subject section</a>. Hopefully, occurrences of non-standard behavior
  49       should be extremely rare in practice however.
  50     </p>
  51 <p>
  52       If you use the standard conforming header includes (in <code class="computeroutput"><span class="identifier">boost</span><span class="special">/</span><span class="identifier">tr1</span><span class="special">/</span><span class="identifier">tr1</span></code>) then these header names can sometimes
  53       conflict with existing standard library headers (for example <code class="computeroutput"><span class="identifier">shared_ptr</span></code> is added to the existing standard
  54       library header <code class="computeroutput"><span class="special">&lt;</span><span class="identifier">memory</span><span class="special">&gt;</span></code> rather than it's own header). These headers
  55       forward on to your existing standard library header in one of two ways: for
  56       gcc it uses <code class="computeroutput"><span class="preprocessor">#include_next</span></code>,
  57       and for other compilers it uses the macro <code class="computeroutput"><span class="identifier">BOOST_TR1_STD_HEADER</span><span class="special">(</span><span class="identifier">header</span><span class="special">)</span></code>
  58       (defined in <a href="../../../boost/tr1/detail/config.hpp" target="_top">boost/tr1/detail/config.hpp</a>)
  59       which evaluates to <code class="computeroutput"><span class="preprocessor">#include</span> <span class="special">&lt;../</span><span class="identifier">include</span><span class="special">/</span><span class="identifier">header</span><span class="special">&gt;</span></code>.
  60       This should work "straight out the box" for most compilers, but does
  61       mean that these headers should <span class="bold"><strong>never</strong></span> be placed
  62       inside a directory called "include" that is already in your compiler's
  63       search path.
  64     </p>
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  67 <td align="left"></td>
  68 <td align="right"><div class="copyright-footer">Copyright &#169; 2005 John Maddock<p>
  69         Distributed under the Boost Software License, Version 1.0. (See accompanying
  70         file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
  71       </p>
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