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Boost Exception documentation update [SVN r44444]
2008-04-15 21:56:34 +00:00
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<title>Tutorial: Cloning and Re-throwing an Exception</title>
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<h1>Boost Exception</h1>
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<div class="RenoIncludeDIV"><h3>Cloning and Re-throwing an Exception</h3>
<p>When you catch a <tt>boost::<span class="RenoLink"><a href="exception.html">exception</a></span></tt>, you can call <tt><span class="RenoLink"><a href="current_exception.html">current_exception</a></span>()</tt> to get an <tt><span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span></tt> object:</p>
<pre>#include &lt;<span class="RenoLink"><a href="exception_cloning_hpp.html">boost/exception_ptr.hpp</a></span>&gt;
#include &lt;boost/thread.hpp&gt;
#include &lt;boost/bind.hpp&gt;
void do_work(); //throws cloning-enabled boost::<span class="RenoLink"><a href="exception.html">exception</a></span>s
void
worker_thread( boost::<span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span> &amp; error )
{
try
{
do_work();
error = boost::<span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span>();
}
catch(
... )
{
error = boost::<span class="RenoLink"><a href="current_exception.html">current_exception</a></span>();
}
}</pre>
Boost Exception documentation fix [SVN r44445]
2008-04-15 22:23:19 +00:00
<p>In the above example, note that <tt><span class="RenoLink"><a href="current_exception.html">current_exception</a></span>()</tt> captures the original type of the exception object. The exception can be thrown again using the <tt><span class="RenoLink"><a href="rethrow_exception.html">rethrow_exception</a></span>()</tt> function:</p>
Boost Exception documentation update [SVN r44444]
2008-04-15 21:56:34 +00:00
<pre>// ...continued
void
work()
{
boost::<span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span> error;
boost::<span class="RenoLink"><a href="http://www.boost.org/doc/html/boost/thread.html">thread</a></span> t( boost::<span class="RenoLink"><a href="http://www.boost.org/libs/bind/bind.html">bind</a></span>(worker_thread,boost::<span class="RenoLink"><a href="http://www.boost.org/doc/html/ref.html">ref</a></span>(error)) );
t.<span class="RenoLink"><a href="http://www.boost.org/doc/html/boost/thread.html">join</a></span>();
if( error )
boost::<span class="RenoLink"><a href="rethrow_exception.html">rethrow_exception</a></span>(error);
}</pre>
Boost Exception documentation fix [SVN r44445]
2008-04-15 22:23:19 +00:00
<p><tt><span class="RenoLink"><a href="current_exception.html">current_exception</a></span>()</tt> could fail to copy the original exception object in the following cases:</p>
Boost Exception documentation update [SVN r44444]
2008-04-15 21:56:34 +00:00
<div><ul><li> if there is not enough memory, in which case the returned <tt><span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span></tt> points to an instance of <tt>std::bad_alloc</tt>, or</li>
Boost Exception documentation fix [SVN r44445]
2008-04-15 22:23:19 +00:00
<li> if <tt><span class="RenoLink"><a href="enable_current_exception.html">enable_current_exception</a></span>()</tt> was not used in the throw-expression passed to the original <tt>throw</tt> statement and the current implementation does not have the necessary compiler-specific support to copy the exception automatically, in which case the returned <tt><span class="RenoLink"><a href="exception_ptr.html">exception_ptr</a></span></tt> points to an instance of <tt><span class="RenoLink"><a href="unknown_exception.html">unknown_exception</a></span></tt>.</li>
Boost Exception documentation update [SVN r44444]
2008-04-15 21:56:34 +00:00
</ul></div>
<p>Regardless, the use of <tt><span class="RenoLink"><a href="current_exception.html">current_exception</a></span>()</tt> and <tt><span class="RenoLink"><a href="rethrow_exception.html">rethrow_exception</a></span>()</tt> in the above examples is well-formed.</p>
</div><h3>See also:</h3>
<div class="RenoPageList"><a href="cloning.html">Tutorial: Transporting of Exceptions between Threads<br/>
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