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25<div class="refentry" lang="en">
26<a name="boost.get"></a><div class="titlepage"></div>
27<div class="refnamediv">
28<h2><span class="refentrytitle">Function get</span></h2>
29<p>boost::get &#8212; <p>Retrieves a value of a specified type from a given
30          <code class="computeroutput"><a href="variant.html" title="Class template variant">variant</a></code>.</p></p>
31</div>
32<h2 xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv-title">Synopsis</h2>
33<div xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" class="refsynopsisdiv"><pre class="synopsis">
34<span class="bold"><strong>template</strong></span>&lt;<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&gt; 
35  <span class="type">U *</span> get(<a href="variant.html" title="Class template variant">variant</a>&lt;T1, T2, ..., TN&gt; * operand);
36<span class="bold"><strong>template</strong></span>&lt;<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&gt; 
37  <span class="type"><span class="bold"><strong>const</strong></span> U *</span> get(<span class="bold"><strong>const</strong></span> <a href="variant.html" title="Class template variant">variant</a>&lt;T1, T2, ..., TN&gt; * operand);
38<span class="bold"><strong>template</strong></span>&lt;<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&gt; 
39  <span class="type">U &amp;</span> get(<a href="variant.html" title="Class template variant">variant</a>&lt;T1, T2, ..., TN&gt; &amp; operand);
40<span class="bold"><strong>template</strong></span>&lt;<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&gt; 
41  <span class="type"><span class="bold"><strong>const</strong></span> U &amp;</span> get(<span class="bold"><strong>const</strong></span> <a href="variant.html" title="Class template variant">variant</a>&lt;T1, T2, ..., TN&gt; &amp; operand);</pre></div>
42<div class="refsect1" lang="en">
43<a name="id1950502"></a><h2>Description</h2>
44<p>The <code class="computeroutput">get</code> function allows run-time checked,
45          type-safe retrieval of the content of the given
46          <code class="computeroutput"><a href="variant.html" title="Class template variant">variant</a></code>. The function succeeds
47          only if the content is of the specified type <code class="computeroutput">U</code>, with
48          failure indicated as described below.</p>
49<p><span class="bold"><strong>Warning</strong></span>: After either
50          <code class="computeroutput">operand</code> or its content is destroyed (e.g., when the
51          given <code class="computeroutput"><a href="variant.html" title="Class template variant">variant</a></code> is assigned a
52          value of different type), the returned reference is invalidated.
53          Thus, significant care and caution must be extended when handling
54          the returned reference.</p>
55<div class="variablelist"><table border="0">
56<col align="left" valign="top">
57<tbody>
58<tr>
59<td>
60<span class="term">Notes:</span></td>
61<td>As part of its guarantee of type-safety, <code class="computeroutput">get</code>
62        enforces <code class="computeroutput">const</code>-correctness. Thus, the specified type
63        <code class="computeroutput">U</code> must be <code class="computeroutput">const</code>-qualified whenever
64        <code class="computeroutput">operand</code> or its content is likewise
65        <code class="computeroutput">const</code>-qualified. The converse, however, is not required:
66        that is, the specified type <code class="computeroutput">U</code> may be
67        <code class="computeroutput">const</code>-qualified even when <code class="computeroutput">operand</code> and its
68        content are not.</td>
69</tr>
70<tr>
71<td>
72<span class="term">Returns:</span></td>
73<td>If passed a pointer, <code class="computeroutput">get</code> returns a pointer to
74        the value content if it is of the specified type <code class="computeroutput">U</code>;
75        otherwise, a null pointer is returned. If passed a reference,
76        <code class="computeroutput">get</code> returns a reference to the value content if it is of
77        the specified type <code class="computeroutput">U</code>; otherwise, an exception is thrown
78        (see below).</td>
79</tr>
80<tr>
81<td>
82<span class="term">Throws:</span></td>
83<td>Overloads taking a
84        <code class="computeroutput"><a href="variant.html" title="Class template variant">variant</a></code> pointer will not
85        throw; the overloads taking a
86        <code class="computeroutput"><a href="variant.html" title="Class template variant">variant</a></code> reference throw
87        <code class="computeroutput"><a href="bad_get.html" title="Class bad_get">bad_get</a></code> if the content is not of
88        the specified type <code class="computeroutput">U</code>.</td>
89</tr>
90<tr>
91<td>
92<span class="term">Rationale:</span></td>
93<td>While visitation via
94        <code class="computeroutput"><a href="apply_visitor.html" title="Function apply_visitor">apply_visitor</a></code>
95        is generally preferred due to its greater safety, <code class="computeroutput">get</code> may
96        may be more convenient in some cases due to its straightforward
97        usage.</td>
98</tr>
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