292 lines
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HTML
292 lines
12 KiB
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1.12.0
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<!-- Local TOC -->
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<div class="local-toc"><ul>
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<li><a class="reference internal" href="#">Exceptions in PCL</a><ul>
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<li><a class="reference internal" href="#adding-a-new-exception">Adding a new Exception</a></li>
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<li><a class="reference internal" href="#using-exceptions">Using Exceptions</a></li>
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<li><a class="reference internal" href="#exceptions-handling">Exceptions handling</a></li>
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<div class="section" id="exceptions-in-pcl">
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<span id="exceptions-guide"></span><h1>Exceptions in PCL</h1>
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<p>There have been a multitude of discussions in the past regarding exceptions in
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PCL (see <a class="reference external" href="http://www.pcl-developers.org/to-throw-or-not-to-throw-td4828759.html">http://www.pcl-developers.org/to-throw-or-not-to-throw-td4828759.html</a>
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for an example). Herein, we discuss the major points with respect to writing
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and using exceptions.</p>
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<div class="section" id="adding-a-new-exception">
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<h2>Adding a new Exception</h2>
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<p>Any new exception should inherit from the <span>PCLException</span> class in
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<code class="docutils literal notranslate"><span class="pre">pcl/exceptions.h</span></code></p>
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<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="cm">/** \class MyException</span>
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<span class="cm"> * \brief An exception that is thrown when I want it.</span>
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<span class="cm"> */</span>
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<span class="k">class</span> <span class="nc">PCL_EXPORTS</span> <span class="nl">MyException</span> <span class="p">:</span> <span class="k">public</span> <span class="n">PCLException</span>
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<span class="p">{</span>
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<span class="k">public</span><span class="o">:</span>
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<span class="n">MyException</span> <span class="p">(</span><span class="k">const</span> <span class="n">std</span><span class="o">::</span><span class="n">string</span><span class="o">&</span> <span class="n">error_description</span><span class="p">,</span>
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<span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">file_name</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">,</span>
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<span class="k">const</span> <span class="kt">char</span><span class="o">*</span> <span class="n">function_name</span> <span class="o">=</span> <span class="nb">NULL</span><span class="p">,</span>
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<span class="kt">unsigned</span> <span class="n">line_number</span> <span class="o">=</span> <span class="mi">0</span><span class="p">)</span>
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<span class="o">:</span> <span class="n">pcl</span><span class="o">::</span><span class="n">PCLException</span> <span class="p">(</span><span class="n">error_description</span><span class="p">,</span> <span class="n">file_name</span><span class="p">,</span> <span class="n">function_name</span><span class="p">,</span> <span class="n">line_number</span><span class="p">)</span> <span class="p">{</span> <span class="p">}</span>
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<span class="p">};</span>
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</pre></div>
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</div>
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</div>
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<div class="section" id="using-exceptions">
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<h2>Using Exceptions</h2>
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<p>For ease of use we provide this macro</p>
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<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="cp">#define PCL_THROW_EXCEPTION (ExceptionName, message)</span>
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<span class="p">{</span>
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<span class="n">std</span><span class="o">::</span><span class="n">ostringstream</span> <span class="n">s</span><span class="p">;</span>
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<span class="n">s</span> <span class="o"><<</span> <span class="n">message</span><span class="p">;</span>
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<span class="k">throw</span> <span class="nf">ExceptionName</span> <span class="p">(</span><span class="n">s</span><span class="p">.</span><span class="n">str</span> <span class="p">(),</span> <span class="n">__FILE__</span><span class="p">,</span> <span class="n">BOOST_CURRENT_FUNCTION</span><span class="p">,</span> <span class="n">__LINE__</span><span class="p">);</span>
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<span class="p">}</span>
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</pre></div>
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</div>
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<p>Then in your code, add:</p>
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<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="k">if</span> <span class="p">(</span><span class="n">my_requirements</span> <span class="o">!=</span> <span class="n">the_parameters_used_</span><span class="p">)</span>
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<span class="n">PCL_THROW_EXCEPTION</span> <span class="p">(</span><span class="n">MyException</span><span class="p">,</span> <span class="s">"my requirements are not met "</span> <span class="o"><<</span> <span class="n">the_parameters_used</span><span class="p">);</span>
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</pre></div>
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</div>
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<p>This will set the file name and the line number thanks to the macro definition.
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Take care of the message: it is the most important part of the exception. You
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can profit of the std::ostringstream used in the macro, so you can append
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variable names to variable values and so on to make it really explicit. Also
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something really important is when the method you are writing <code class="docutils literal notranslate"><span class="pre">can</span></code> throw an
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exception, please add this to the the function documentation:</p>
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<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="cm">/** Function that does cool stuff</span>
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<span class="cm"> * \param nb number of points</span>
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<span class="cm"> * \throws MyException</span>
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<span class="cm"> */</span>
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<span class="kt">void</span>
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<span class="nf">myFunction</span> <span class="p">(</span><span class="kt">int</span> <span class="n">nb</span><span class="p">);</span>
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</pre></div>
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</div>
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<p>This will be parsed by Doxygen and made available in the generated API
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documentation so the person that would use your function knows that they have
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to deal with an exception called <code class="docutils literal notranslate"><span class="pre">MyException</span></code>.</p>
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</div>
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<div class="section" id="exceptions-handling">
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<h2>Exceptions handling</h2>
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<p>To properly handle exceptions you need to use the <code class="docutils literal notranslate"><span class="pre">try</span></code>… <code class="docutils literal notranslate"><span class="pre">catch</span></code> block.</p>
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<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="c1">// Here we call myFunction which can throw MyException</span>
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<span class="k">try</span>
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<span class="p">{</span>
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<span class="n">myObject</span><span class="p">.</span><span class="n">myFunction</span> <span class="p">(</span><span class="n">some_number</span><span class="p">);</span>
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<span class="c1">// You can put more exceptions throwing instruction within same try block</span>
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<span class="p">}</span>
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<span class="c1">// We catch only MyException to be very specific</span>
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<span class="k">catch</span> <span class="p">(</span><span class="n">pcl</span><span class="o">::</span><span class="n">MyException</span><span class="o">&</span> <span class="n">e</span><span class="p">)</span>
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<span class="p">{</span>
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<span class="c1">// Code to deal with the exception maybe changing myObject.the_parameters_used_</span>
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<span class="p">}</span>
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<span class="c1">// Here we catch any exception</span>
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<span class="cp">#if 0</span><span class="c"></span>
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<span class="c">catch (exception& e)</span>
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<span class="c">{</span>
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<span class="c"> // Code to deal with the exception maybe changing myObject.the_parameters_used_</span>
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<span class="c">}</span>
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<span class="cp">#endif</span>
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</pre></div>
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</div>
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<p>Exceptions handling is really context dependent so there is no general
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rule that can be applied but here are some of the most used guidelines:</p>
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<blockquote>
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<div><ul class="simple">
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<li>exit with some error if the exception is critical</li>
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<li>modify the parameters for the function that threw the exception and recall it again</li>
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<li>throw an exception with a meaningful message saying that you encountred an exception</li>
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<li>continue (really bad)</li>
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</ul>
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</div></blockquote>
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</div>
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</div>
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<p>
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© Copyright
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