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<div class="appendix">
<div class="titlepage"><div><div><h1 class="title">
<a name="chapter-refptr"></a>Appendix A. The RefPtr smartpointer</h1></div></div></div>
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<p><b>Table of Contents</b></p>
<ul class="toc">
<li><span class="section"><a href="chapter-refptr.html#sec-refptr-copying">Copying</a></span></li>
<li><span class="section"><a href="sec-refptr-dereferencing.html">Dereferencing</a></span></li>
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<li><span class="section"><a href="sec-refptr-checking-for-null.html">Checking for nullptr</a></span></li>
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<p>
<code class="classname">Glib::RefPtr</code> is a smartpointer. Specifically, it is a
reference-counting smartpointer. You might be familiar with
<code class="classname">std::unique_ptr<></code>
and <code class="classname">std::shared_ptr<></code>, which are also smartpointers.
In <span class="application">gtkmm</span>-4.0 <code class="classname">Glib::RefPtr<></code> is an alias for
<code class="classname">std::shared_ptr<></code>,
which is reference-counting. <code class="classname">Glib::RefPtr<></code> was introduced
long before there was a reference-counting smartpointer in the C++ Standard Library.
</p>
<p>
If you make your own <code class="classname">Glib::ObjectBase</code>-derived classes with
<code class="methodname">create()</code> methods that return a <code class="classname">Glib::RefPtr</code>,
you must use <code class="function">Glib::make_refptr_for_instance()</code> in your
<code class="methodname">create()</code> methods. This function creates a <code class="classname">std::shared_ptr</code>
with a special deleter, which handles the reference-count for the wrapped C object.
</p>
<p><a class="ulink" href="https://gnome.pages.gitlab.gnome.org/glibmm/group__RefPtr.html" target="_top">Reference</a></p>
<p>A smartpointer acts much like a normal pointer. Here are a few examples.</p>
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<a name="sec-refptr-copying"></a>Copying</h2></div></div></div>
<p>
You can copy <code class="classname">RefPtr</code>s, just like normal pointers. But
unlike normal pointers, you don't need to worry about deleting the underlying
instance.
</p>
<pre class="programlisting"><code class="code">auto refPixbuf = Gdk::Pixbuf::create_from_file(filename);
auto refPixbuf2 = refPixbuf;
</code></pre>
<p>
Of course this means that you can store <code class="classname">RefPtr</code>s in
standard containers, such as <code class="classname">std::vector</code> or
<code class="classname">std::list</code>.</p>
<pre class="programlisting"><code class="code">std::list<Glib::RefPtr<Gdk::Pixbuf>> listPixbufs;
auto refPixbuf = Gdk::Pixbuf::create_from_file(filename);
listPixbufs.push_back(refPixbuf);
</code></pre>
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