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<title>Function get</title>
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<a name="get"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle">Function get</span></h2>
<p>boost::get — <p>Retrieves a value of a specified type from a given
<code class="computeroutput"><a href="boost/variant.html" title="Class template variant">variant</a></code>.</p></p>
</div>
<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis">
<span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> U, <span class="bold"><strong>typename</strong></span> T1, <span class="bold"><strong>typename</strong></span> T2, ..., <span class="bold"><strong>typename</strong></span> TN>
<span class="type">U *</span> get(<a href="boost/variant.html" title="Class template variant">variant</a><T1, T2, ..., TN> * operand);
<span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> U, <span class="bold"><strong>typename</strong></span> T1, <span class="bold"><strong>typename</strong></span> T2, ..., <span class="bold"><strong>typename</strong></span> TN>
<span class="type"><span class="bold"><strong>const</strong></span> U *</span> get(<span class="bold"><strong>const</strong></span> <a href="boost/variant.html" title="Class template variant">variant</a><T1, T2, ..., TN> * operand);
<span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> U, <span class="bold"><strong>typename</strong></span> T1, <span class="bold"><strong>typename</strong></span> T2, ..., <span class="bold"><strong>typename</strong></span> TN>
<span class="type">U &</span> get(<a href="boost/variant.html" title="Class template variant">variant</a><T1, T2, ..., TN> & operand);
<span class="bold"><strong>template</strong></span><<span class="bold"><strong>typename</strong></span> U, <span class="bold"><strong>typename</strong></span> T1, <span class="bold"><strong>typename</strong></span> T2, ..., <span class="bold"><strong>typename</strong></span> TN>
<span class="type"><span class="bold"><strong>const</strong></span> U &</span> get(<span class="bold"><strong>const</strong></span> <a href="boost/variant.html" title="Class template variant">variant</a><T1, T2, ..., TN> & operand);</pre></div>
<div class="refsect1" lang="en">
<a name="id2839339"></a><h2>Description</h2>
<p>The <code class="computeroutput">get</code> function allows run-time checked,
type-safe retrieval of the content of the given
<code class="computeroutput"><a href="boost/variant.html" title="Class template variant">variant</a></code>. The function succeeds
only if the content is of the specified type <code class="computeroutput">U</code>, with
failure indicated as described below.</p>
<p><span class="bold"><strong>Warning</strong></span>: After either
<code class="computeroutput">operand</code> or its content is destroyed (e.g., when the
given <code class="computeroutput"><a href="boost/variant.html" title="Class template variant">variant</a></code> is assigned a
value of different type), the returned reference is invalidated.
Thus, significant care and caution must be extended when handling
the returned reference.</p>
<p><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Notes</span></b>:
As part of its guarantee of type-safety, <code class="computeroutput">get</code>
enforces <code class="computeroutput">const</code>-correctness. Thus, the specified type
<code class="computeroutput">U</code> must be <code class="computeroutput">const</code>-qualified whenever
<code class="computeroutput">operand</code> or its content is likewise
<code class="computeroutput">const</code>-qualified. The converse, however, is not required:
that is, the specified type <code class="computeroutput">U</code> may be
<code class="computeroutput">const</code>-qualified even when <code class="computeroutput">operand</code> and its
content are not.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Returns</span></b>:
If passed a pointer, <code class="computeroutput">get</code> returns a pointer to
the value content if it is of the specified type <code class="computeroutput">U</code>;
otherwise, a null pointer is returned. If passed a reference,
<code class="computeroutput">get</code> returns a reference to the value content if it is of
the specified type <code class="computeroutput">U</code>; otherwise, an exception is thrown
(see below).<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Throws</span></b>:
Overloads taking a
<code class="computeroutput"><a href="boost/variant.html" title="Class template variant">variant</a></code> pointer will not
throw; the overloads taking a
<code class="computeroutput"><a href="boost/variant.html" title="Class template variant">variant</a></code> reference throw
<code class="computeroutput"><a href="bad_get.html" title="Class bad_get">bad_get</a></code> if the content is not of
the specified type <code class="computeroutput">U</code>.<br><b xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision"><span class="term">Rationale</span></b>:
While visitation via
<code class="computeroutput"><a href="apply_visitor.html" title="Function apply_visitor">apply_visitor</a></code>
is generally prefered due to its greater safety, <code class="computeroutput">get</code> may
may be more convenient in some cases due to its straightforward
usage.</p>
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