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| <h2><span class="refentrytitle">Function get</span></h2> |
| <p>boost::get — Retrieves a value of a specified type from a given |
| <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code>.</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="comment">// In header: <<a class="link" href="../variant/reference.html#header.boost.variant.get_hpp" title="Header <boost/variant/get.hpp>">boost/variant/get.hpp</a>> |
| |
| </span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U<span class="special">,</span> <span class="keyword">typename</span> T1<span class="special">,</span> <span class="keyword">typename</span> T2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> TN<span class="special">></span> |
| <span class="identifier">U</span> <span class="special">*</span> <span class="identifier">get</span><span class="special">(</span><a class="link" href="variant.html" title="Class template variant">variant</a><span class="special"><</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">></span> <span class="special">*</span> operand<span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U<span class="special">,</span> <span class="keyword">typename</span> T1<span class="special">,</span> <span class="keyword">typename</span> T2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> TN<span class="special">></span> |
| <span class="keyword">const</span> <span class="identifier">U</span> <span class="special">*</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="variant.html" title="Class template variant">variant</a><span class="special"><</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">></span> <span class="special">*</span> operand<span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U<span class="special">,</span> <span class="keyword">typename</span> T1<span class="special">,</span> <span class="keyword">typename</span> T2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> TN<span class="special">></span> |
| <span class="identifier">U</span> <span class="special">&</span> <span class="identifier">get</span><span class="special">(</span><a class="link" href="variant.html" title="Class template variant">variant</a><span class="special"><</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">></span> <span class="special">&</span> operand<span class="special">)</span><span class="special">;</span> |
| <span class="keyword">template</span><span class="special"><</span><span class="keyword">typename</span> U<span class="special">,</span> <span class="keyword">typename</span> T1<span class="special">,</span> <span class="keyword">typename</span> T2<span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="keyword">typename</span> TN<span class="special">></span> |
| <span class="keyword">const</span> <span class="identifier">U</span> <span class="special">&</span> <span class="identifier">get</span><span class="special">(</span><span class="keyword">const</span> <a class="link" href="variant.html" title="Class template variant">variant</a><span class="special"><</span><span class="identifier">T1</span><span class="special">,</span> <span class="identifier">T2</span><span class="special">,</span> <span class="special">...</span><span class="special">,</span> <span class="identifier">TN</span><span class="special">></span> <span class="special">&</span> operand<span class="special">)</span><span class="special">;</span></pre></div> |
| <div class="refsect1"> |
| <a name="id3087317"></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 class="link" href="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 class="link" href="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> |
| <div class="variablelist"><table border="0"> |
| <col align="left" valign="top"> |
| <tbody> |
| <tr> |
| <td><p><span class="term">Notes:</span></p></td> |
| <td>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.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Returns:</span></p></td> |
| <td>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).</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Throws:</span></p></td> |
| <td>Overloads taking a |
| <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code> pointer will not |
| throw; the overloads taking a |
| <code class="computeroutput"><a class="link" href="variant.html" title="Class template variant">variant</a></code> reference throw |
| <code class="computeroutput"><a class="link" 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>.</td> |
| </tr> |
| <tr> |
| <td><p><span class="term">Rationale:</span></p></td> |
| <td>While visitation via |
| <code class="computeroutput"><a class="link" href="apply_visitor.html" title="Function apply_visitor">apply_visitor</a></code> |
| is generally preferred due to its greater safety, <code class="computeroutput">get</code> may |
| may be more convenient in some cases due to its straightforward |
| usage.</td> |
| </tr> |
| </tbody> |
| </table></div> |
| </div> |
| </div> |
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| <td align="left"></td> |
| <td align="right"><div class="copyright-footer">Copyright © 2002, 2003 Eric Friedman, Itay Maman<p>Distributed under the Boost Software License, Version 1.0. |
| (See accompanying file <code class="filename">LICENSE_1_0.txt</code> or copy at |
| <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>) |
| </p> |
| </div></td> |
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