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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::</span>dynamic_extent</h1>
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<div id="contentSub"><span class="subpages">&lt; <a href="cpp.html">cpp</a>&lrm; | <a href="cpp-container.html">container</a>&lrm; | <a href="cpp-container-span.html">span</a></span></div>
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<div>&#23450;&#20041;&#20110;&#22836;&#25991;&#20214; <code><a href="cpp-header-span.html">&lt;span&gt;</a></code></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">inline</span> <span class="kw4">constexpr</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> dynamic_extent <span class="sy1">=</span> <a href="cpp-types-numeric_limits.html"><span class="kw344">std::<span class="me2">numeric_limits</span></span></a><span class="sy1">&lt;</span><a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a><span class="sy1">&gt;</span><span class="sy4">::</span><span class="me2">max</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx20">(C++20 &#36215;)</span></td>
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<p><code>std::dynamic_extent</code> &#26159; <span class="t-lc"><a href="cpp-types-size_t.html">std::size_t</a></span> &#31867;&#22411;&#24120;&#37327;&#65292;&#29992;&#20110;&#21306;&#21035;&#25317;&#26377;&#38745;&#24577;&#21644;&#21160;&#24577;&#38271;&#24230;&#30340; <a href="cpp-container-span.html"><tt>std::span</tt></a> &#12290;</p>
<h3><span class="mw-headline" id=".E6.B3.A8.E8.A7.A3">&#27880;&#35299;</span></h3>
<p>&#30001;&#20110; <code>std::size_t</code> &#26159;&#26080;&#31526;&#21495;&#31867;&#22411;&#65292;&#31561;&#20215;&#30340;&#23450;&#20041;&#26159;&#65306;</p>
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<pre class="de1"><span class="kw1">inline</span> <span class="kw4">constexpr</span> <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> dynamic_extent <span class="sy1">=</span> <span class="sy2">-</span><span class="nu0">1</span><span class="sy4">;</span></pre></div>
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<p>&#35265;<a href="cpp-language-implicit_conversion.html#.E6.95.B4.E5.9E.8B.E8.BD.AC.E6.8D.A2">&#25972;&#22411;&#36716;&#25442;</a>&#12290;</p>
<h3><span class="mw-headline" id=".E7.A4.BA.E4.BE.8B">&#31034;&#20363;</span></h3>
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<pre class="de1"><span class="co2">#include &lt;array&gt;</span>
<span class="co2">#include &lt;cassert&gt;</span>
<span class="co2">#include &lt;cstddef&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;span&gt;</span>
<span class="co2">#include &lt;string_view&gt;</span>
<span class="co2">#include &lt;vector&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span>
<span class="br0">{</span>
<span class="kw4">auto</span> print <span class="sy1">=</span> <span class="br0">[</span><span class="br0">]</span><span class="br0">(</span><a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> <span class="kw4">const</span> name, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> ex<span class="br0">)</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> name <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;, &quot;</span><span class="sy4">;</span>
<span class="kw1">if</span> <span class="br0">(</span>ex <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">dynamic_extent</span><span class="br0">)</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;dynamic extent<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="br0">}</span> <span class="kw1">else</span> <span class="br0">{</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;static extent = &quot;</span> <span class="sy1">&lt;&lt;</span> ex <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> a<span class="br0">[</span><span class="br0">]</span><span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span><span class="br0">}</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span> span1<span class="br0">{</span>a<span class="br0">}</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&quot;span1&quot;</span>, span1.<span class="me1">extent</span><span class="br0">)</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span><span class="sy1">&lt;</span><span class="kw4">int</span>, std<span class="sy4">::</span><span class="me2">dynamic_extent</span><span class="sy1">&gt;</span> span2<span class="br0">{</span>a<span class="br0">}</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&quot;span2&quot;</span>, span2.<span class="me1">extent</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a> ar<span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span><span class="br0">}</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span> span3<span class="br0">{</span>ar<span class="br0">}</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&quot;span3&quot;</span>, span3.<span class="me1">extent</span><span class="br0">)</span><span class="sy4">;</span>
<a href="cpp-container-vector.html"><span class="kw1269">std::<span class="me2">vector</span></span></a> v<span class="br0">{</span><span class="nu0">1</span>,<span class="nu0">2</span>,<span class="nu0">3</span>,<span class="nu0">4</span>,<span class="nu0">5</span><span class="br0">}</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span> span4<span class="br0">{</span>v<span class="br0">}</span><span class="sy4">;</span>
print<span class="br0">(</span><span class="st0">&quot;span4&quot;</span>, span4.<span class="me1">extent</span><span class="br0">)</span><span class="sy4">;</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">span1, static extent = 5
span2, dynamic extent
span3, static extent = 5
span4, dynamic extent</pre></div>
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<h3><span class="mw-headline" id=".E5.8F.82.E9.98.85">&#21442;&#38405;</span></h3>
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<div><span class="t-lines"><span><span class="t-mark-rev t-since-cxx20">(C++20)</span></span></span></div>
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<td>&#23545;&#35937;&#30340;&#36830;&#32493;&#24207;&#21015;&#19978;&#30340;&#26080;&#25152;&#26377;&#26435;&#35270;&#22270;<br />
<span class="t-mark">(&#31867;&#27169;&#26495;)</span></td>
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