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<section id="conventions">
<h1>Conventions<a class="headerlink" href="#conventions" title="Permalink to this heading">#</a></h1>
<p>The Arrow C++ API follows a few simple guidelines. As with many rules,
there may be exceptions.</p>
<section id="language-version">
<h2>Language version<a class="headerlink" href="#language-version" title="Permalink to this heading">#</a></h2>
<p>Starting with version 10.0, Arrow C++ is C++17-compatible.</p>
</section>
<section id="namespacing">
<h2>Namespacing<a class="headerlink" href="#namespacing" title="Permalink to this heading">#</a></h2>
<p>All the Arrow API (except macros) is namespaced inside a <code class="docutils literal notranslate"><span class="pre">arrow</span></code> namespace,
and nested namespaces thereof.</p>
</section>
<section id="safe-pointers">
<h2>Safe pointers<a class="headerlink" href="#safe-pointers" title="Permalink to this heading">#</a></h2>
<p>Arrow objects are usually passed and stored using safe pointers – most of
the time <code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">std::shared_ptr</span></code> but sometimes also <code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">std::unique_ptr</span></code>.</p>
</section>
<section id="immutability">
<h2>Immutability<a class="headerlink" href="#immutability" title="Permalink to this heading">#</a></h2>
<p>Many Arrow objects are immutable: once constructed, their logical properties
cannot change anymore. This makes it possible to use them in multi-threaded
scenarios without requiring tedious and error-prone synchronization.</p>
<p>There are obvious exceptions to this, such as IO objects or mutable data buffers.</p>
</section>
<section id="error-reporting">
<h2>Error reporting<a class="headerlink" href="#error-reporting" title="Permalink to this heading">#</a></h2>
<p>Most APIs indicate a successful or erroneous outcome by returning a
<a class="reference internal" href="api/support.html#_CPPv4N5arrow6StatusE" title="arrow::Status"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::Status</span></code></a> instance. Arrow doesn’t throw exceptions of its
own, but third-party exceptions might propagate through, especially
<code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">std::bad_alloc</span></code> (but Arrow doesn’t use the standard allocators for
large data).</p>
<p>When an API can return either an error code or a successful value, it usually
does so by returning the template class
<a class="reference internal" href="api/support.html#_CPPv4I0EN5arrow6ResultE" title="arrow::Result"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::Result</span></code></a>. However,
some APIs (usually deprecated) return <a class="reference internal" href="api/support.html#_CPPv4N5arrow6StatusE" title="arrow::Status"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::Status</span></code></a> and pass the
result value as an out-pointer parameter.</p>
<p>Here is an example of checking the outcome of an operation:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="k">const</span><span class="w"> </span><span class="kt">int64_t</span><span class="w"> </span><span class="n">buffer_size</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4096</span><span class="p">;</span>
<span class="k">auto</span><span class="w"> </span><span class="n">maybe_buffer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">AllocateBuffer</span><span class="p">(</span><span class="n">buffer_size</span><span class="p">,</span><span class="w"> </span><span class="o">&amp;</span><span class="n">buffer</span><span class="p">);</span>
<span class="k">if</span><span class="w"> </span><span class="p">(</span><span class="o">!</span><span class="n">maybe_buffer</span><span class="p">.</span><span class="n">ok</span><span class="p">())</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="c1">// ... handle error</span>
<span class="p">}</span><span class="w"> </span><span class="k">else</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">arrow</span><span class="o">::</span><span class="n">Buffer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">buffer</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="o">*</span><span class="n">maybe_buffer</span><span class="p">;</span>
<span class="w"> </span><span class="c1">// ... use allocated buffer</span>
<span class="p">}</span>
</pre></div>
</div>
<p>If the caller function itself returns a <a class="reference internal" href="api/support.html#_CPPv4I0EN5arrow6ResultE" title="arrow::Result"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::Result</span></code></a> or
<a class="reference internal" href="api/support.html#_CPPv4N5arrow6StatusE" title="arrow::Status"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::Status</span></code></a> and wants to propagate any non-successful outcome, two
convenience macros are available:</p>
<ul class="simple">
<li><p><a class="reference internal" href="api/support.html#c.ARROW_RETURN_NOT_OK" title="ARROW_RETURN_NOT_OK"><code class="xref c c-macro docutils literal notranslate"><span class="pre">ARROW_RETURN_NOT_OK</span></code></a> takes a <a class="reference internal" href="api/support.html#_CPPv4N5arrow6StatusE" title="arrow::Status"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::Status</span></code></a> parameter
and returns it if not successful.</p></li>
<li><p><a class="reference internal" href="api/support.html#c.ARROW_ASSIGN_OR_RAISE" title="ARROW_ASSIGN_OR_RAISE"><code class="xref c c-macro docutils literal notranslate"><span class="pre">ARROW_ASSIGN_OR_RAISE</span></code></a> takes a <a class="reference internal" href="api/support.html#_CPPv4I0EN5arrow6ResultE" title="arrow::Result"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::Result</span></code></a> parameter,
assigns its result to a <em>lvalue</em> if successful, or returns the corresponding
<a class="reference internal" href="api/support.html#_CPPv4N5arrow6StatusE" title="arrow::Status"><code class="xref cpp cpp-class docutils literal notranslate"><span class="pre">arrow::Status</span></code></a> on error.</p></li>
</ul>
<p>For example:</p>
<div class="highlight-cpp notranslate"><div class="highlight"><pre><span></span><span class="n">arrow</span><span class="o">::</span><span class="n">Status</span><span class="w"> </span><span class="nf">DoSomething</span><span class="p">()</span><span class="w"> </span><span class="p">{</span>
<span class="w"> </span><span class="k">const</span><span class="w"> </span><span class="kt">int64_t</span><span class="w"> </span><span class="n">buffer_size</span><span class="w"> </span><span class="o">=</span><span class="w"> </span><span class="mi">4096</span><span class="p">;</span>
<span class="w"> </span><span class="n">std</span><span class="o">::</span><span class="n">shared_ptr</span><span class="o">&lt;</span><span class="n">arrow</span><span class="o">::</span><span class="n">Buffer</span><span class="o">&gt;</span><span class="w"> </span><span class="n">buffer</span><span class="p">;</span>
<span class="w"> </span><span class="n">ARROW_ASSIGN_OR_RAISE</span><span class="p">(</span><span class="n">buffer</span><span class="p">,</span><span class="w"> </span><span class="n">arrow</span><span class="o">::</span><span class="n">AllocateBuffer</span><span class="p">(</span><span class="n">buffer_size</span><span class="p">));</span>
<span class="w"> </span><span class="c1">// ... allocation successful, do something with buffer below</span>
<span class="w"> </span><span class="c1">// return success at the end</span>
<span class="w"> </span><span class="k">return</span><span class="w"> </span><span class="n">Status</span><span class="o">::</span><span class="n">OK</span><span class="p">();</span>
<span class="p">}</span>
</pre></div>
</div>
<div class="admonition seealso">
<p class="admonition-title">See also</p>
<p><a class="reference internal" href="api/support.html"><span class="doc">API reference for error reporting</span></a></p>
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