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<p class="heading-quote">
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<q>...one of the most highly
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regarded and expertly designed C++ library projects in the
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world.</q> <span class="heading-attribution">— <a href=
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"http://www.gotw.ca/" class="external">Herb Sutter</a> and <a href=
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<div class="titlepage"><div><div><h2 class="title" style="clear: both">Variations</h2></div></div></div>
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<p>You can of course choose your own <code>E</code> type so long as it has standard layout
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and is trivially copyable. You would declare that with <a href="reference/result_c/#standardese-CXX_DECLARE_RESULT" class="api-reference"><i class="fa fa-book" aria-hidden="true"></i> CXX_DECLARE_RESULT(t_ident, t_decl, e_ident, e_decl)</a>
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,
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refer to it with <a href="reference/result_c/#standardese-CXX_RESULT" class="api-reference"><i class="fa fa-book" aria-hidden="true"></i> CXX_RESULT(t_ident, e_ident)</a>
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and need to do your own
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decoding of errors from your <code>E</code> type. By using the <code>_EC</code> postfixed macros,
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you are in fact using <code>E =</code></p>
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<div class="highlight"><pre class="chroma"><code class="language-c" data-lang="c"><span class="k">struct</span> <span class="n">cxx_error_code</span>
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<span class="p">{</span>
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<span class="kt">int</span> <span class="n">code</span><span class="p">;</span>
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<span class="kt">void</span> <span class="o">*</span><span class="n">category</span><span class="p">;</span>
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<span class="p">};</span></code></pre></div>
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<p>… which is declared for you by <code>result.h</code>.</p>
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<p>Outcome’s C support was designed assuming that you do not wish to penalise the performance
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of C++ code calling these C-compatible C++ functions, but if you don’t care
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about that, then always setting <code>errno</code> to any error in a <code>result<T></code> is easily
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implemented and thus the natural C use pattern becomes available:</p>
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<div class="highlight"><pre class="chroma"><code class="language-c" data-lang="c"><span class="k">extern</span> <span class="n">size_t</span> <span class="nf">to_string</span><span class="p">(</span><span class="kt">char</span> <span class="o">*</span><span class="n">buffer</span><span class="p">,</span> <span class="n">size_t</span> <span class="n">bufferlen</span><span class="p">,</span> <span class="kt">int</span> <span class="n">v</span><span class="p">);</span>
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<span class="p">...</span>
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<span class="n">size_t</span> <span class="n">len</span> <span class="o">=</span> <span class="n">to_string</span><span class="p">(</span><span class="n">buffer</span><span class="p">,</span> <span class="k">sizeof</span><span class="p">(</span><span class="n">buffer</span><span class="p">),</span> <span class="n">v</span><span class="p">);</span>
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<span class="k">if</span><span class="p">(</span><span class="n">errno</span> <span class="o">!=</span> <span class="mi">0</span><span class="p">)</span>
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<span class="p">...</span></code></pre></div>
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<p>Implementing this via boilerplate generating script is straightforward,
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and is left as an exercise to the interested reader.</p>
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</div><p><small>Last revised: December 05, 2018 at 14:18:52 UTC</small></p>
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