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<h1 id="firstHeading" class="firstHeading"><code>std::span</code> &#30340;&#25512;&#23548;&#25351;&#24341;</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">template</span> <span class="sy1">&lt;</span><span class="kw1">class</span> It, <span class="kw1">class</span> EndOrSize<span class="sy1">&gt;</span><br />
span<span class="br0">(</span>It, EndOrSize<span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> span<span class="sy1">&lt;</span><a href="cpp-types-remove_reference.html"><span class="kw607">std::<span class="me2">remove_reference_t</span></span></a><span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">iter_reference_t</span><span class="sy1">&lt;</span>It<span class="sy1">&gt;&gt;&gt;</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">&gt;</span><br />
span<span class="br0">(</span>T <span class="br0">(</span><span class="sy3">&amp;</span><span class="br0">)</span><span class="br0">[</span>N<span class="br0">]</span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> span<span class="sy1">&lt;</span>T, N<span class="sy1">&gt;</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">&gt;</span><br />
span<span class="br0">(</span><a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1">&lt;</span>T, N<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> span<span class="sy1">&lt;</span>T, N<span class="sy1">&gt;</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">class</span> T, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> N<span class="sy1">&gt;</span><br />
span<span class="br0">(</span><span class="kw4">const</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a><span class="sy1">&lt;</span>T, N<span class="sy1">&gt;</span><span class="sy3">&amp;</span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> span<span class="sy1">&lt;</span><span class="kw4">const</span> T, N<span class="sy1">&gt;</span><span class="sy4">;</span></span></div>
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<div><span class="mw-geshi cpp source-cpp"><span class="kw1">template</span><span class="sy1">&lt;</span><span class="kw1">class</span> R<span class="sy1">&gt;</span><br />
span<span class="br0">(</span>R<span class="sy3">&amp;&amp;</span><span class="br0">)</span> <span class="sy2">-</span><span class="sy1">&gt;</span> span<span class="sy1">&lt;</span><a href="cpp-types-remove_reference.html"><span class="kw607">std::<span class="me2">remove_reference_t</span></span></a><span class="sy1">&lt;</span>std<span class="sy4">::</span><span class="me2">ranges</span><span class="sy4">::</span><span class="me2">range_reference_t</span><span class="sy1">&lt;</span>R<span class="sy1">&gt;&gt;&gt;</span><span class="sy4">;</span></span></div>
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<p>&#20026; <code>span</code> &#25552;&#20379;&#19979;&#21015;<a href="cpp-language-class_template_argument_deduction.html">&#25512;&#23548;&#25351;&#24341;</a>&#12290;</p>
<p><span class="t-v">(1)</span> &#20801;&#35768;&#20174;&#36845;&#20195;&#22120;-&#21736;&#20301;&#23545;&#25512;&#23548;&#20803;&#32032;&#31867;&#22411;&#12290;&#27492;&#37325;&#36733;&#20165;&#33509; <code>It</code> &#28385;&#36275; <a href="cpp-iterator-contiguous_iterator.html"><code>contiguous_iterator</code></a> &#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#12290;</p>
<p><span class="t-v">(2-4)</span> &#20801;&#35768;&#20174;&#20869;&#24314;&#25968;&#32452;&#19982; <span class="t-lc"><a href="cpp-container-array.html">std::array</a></span> &#25512;&#23548;&#38745;&#24577;&#38271;&#24230;&#12290;</p>
<p><span class="t-v">(5)</span> &#20801;&#35768;&#20174;&#33539;&#22260;&#25512;&#23548;&#20803;&#32032;&#31867;&#22411;&#12290;&#27492;&#37325;&#36733;&#20165;&#33509; <code>R</code> &#28385;&#36275; <a href="cpp-ranges-contiguous_range.html"><code>contiguous_range</code></a> &#25165;&#21442;&#19982;&#37325;&#36733;&#20915;&#35758;&#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;cstddef&gt;</span>
<span class="co2">#include &lt;iomanip&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">void</span> print<span class="br0">(</span><a href="cpp-string-basic_string_view.html"><span class="kw1248">std::<span class="me2">string_view</span></span></a> rem <span class="sy1">=</span> <span class="st0">&quot;&quot;</span>, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> size_of <span class="sy1">=</span> <span class="nu0">0</span>, <a href="cpp-types-size_t.html"><span class="kw100">std::<span class="me2">size_t</span></span></a> extent <span class="sy1">=</span> <span class="nu0">0</span><span class="br0">)</span> <span class="br0">{</span>
<span class="kw1">if</span> <span class="br0">(</span>rem.<span class="me1">empty</span><span class="br0">(</span><span class="br0">)</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;name &#9474; sizeof &#9474; extent<span class="es1">\n</span>&#9472;&#9472;&#9472;&#9472;&#9472;&#9532;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9532;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;<span class="es1">\n</span>&quot;</span><span class="sy4">;</span>
<span class="kw1">return</span><span class="sy4">;</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> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">4</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> rem <span class="sy1">&lt;&lt;</span> <span class="st0">&quot; &#9474; &quot;</span> <span class="sy1">&lt;&lt;</span> <a href="cpp-io-manip-setw.html"><span class="kw1797">std::<span class="me2">setw</span></span></a><span class="br0">(</span><span class="nu0">6</span><span class="br0">)</span> <span class="sy1">&lt;&lt;</span> size_of <span class="sy1">&lt;&lt;</span> <span class="st0">&quot; &#9474; &quot;</span><span class="sy4">;</span>
<span class="kw1">if</span> <span class="br0">(</span>extent <span class="sy1">==</span> std<span class="sy4">::</span><span class="me2">dynamic_extent</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&quot;</span><span class="sy4">;</span>
<span class="kw1">else</span>
<a href="cpp-io-cout.html"><span class="kw1758">std::<span class="me2">cout</span></span></a> <span class="sy1">&lt;&lt;</span> extent<span class="sy4">;</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">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="br0">}</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</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>
print<span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span> s1 <span class="br0">{</span><a href="cpp-iterator-begin.html"><span class="kw676">std::<span class="me2">begin</span></span></a><span class="br0">(</span>a<span class="br0">)</span>, <a href="cpp-iterator-end.html"><span class="kw680">std::<span class="me2">end</span></span></a><span class="br0">(</span>a<span class="br0">)</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// &#25351;&#24341; (1)</span>
print<span class="br0">(</span><span class="st0">&quot;s1&quot;</span>, sizeof s1, s1.<span class="me1">extent</span><span class="br0">)</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span> s2 <span class="br0">{</span><a href="cpp-iterator-begin.html"><span class="kw676">std::<span class="me2">begin</span></span></a><span class="br0">(</span>a<span class="br0">)</span>, <span class="nu0">3</span><span class="br0">}</span><span class="sy4">;</span> <span class="co1">// &#25351;&#24341; (1)</span>
print<span class="br0">(</span><span class="st0">&quot;s2&quot;</span>, sizeof s2, s2.<span class="me1">extent</span><span class="br0">)</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span> s3 <span class="br0">{</span>a<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// &#25351;&#24341; (2)</span>
print<span class="br0">(</span><span class="st0">&quot;s3&quot;</span>, sizeof s3, s3.<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><span class="sy1">&gt;</span> s4 <span class="br0">{</span>a<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// &#19981;&#20351;&#29992;&#25351;&#24341;&#65292;&#21046;&#20316;&#21160;&#24577; span</span>
print<span class="br0">(</span><span class="st0">&quot;s4&quot;</span>, sizeof s4, s4.<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> arr <span class="br0">{</span><span class="nu0">6</span>, <span class="nu0">7</span>, <span class="nu0">8</span><span class="br0">}</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span> s5 <span class="br0">{</span>arr<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// &#25351;&#24341; (3)</span>
print<span class="br0">(</span><span class="st0">&quot;s5&quot;</span>, sizeof s5, s5.<span class="me1">extent</span><span class="br0">)</span><span class="sy4">;</span>
s5<span class="br0">[</span><span class="nu0">0</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu0">42</span><span class="sy4">;</span> <span class="co1">// OK, element_type is &#39;int&#39;</span>
<span class="kw4">const</span> <a href="cpp-container-array.html"><span class="kw1268">std::<span class="me2">array</span></span></a> arr2 <span class="br0">{</span><span class="nu0">9</span>, <span class="nu0">10</span>, <span class="nu0">11</span><span class="br0">}</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span> s6 <span class="br0">{</span>arr2<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// &#25351;&#24341; (4)</span>
print<span class="br0">(</span><span class="st0">&quot;s6&quot;</span>, sizeof s6, s6.<span class="me1">extent</span><span class="br0">)</span><span class="sy4">;</span>
<span class="co1">// s6[0] = 42; // Error: element_type is &#39;const int&#39;</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">66</span>, <span class="nu0">69</span>, <span class="nu0">99</span><span class="br0">}</span><span class="sy4">;</span>
std<span class="sy4">::</span><span class="me2">span</span> s7 <span class="br0">{</span>v<span class="br0">}</span><span class="sy4">;</span> <span class="co1">// &#25351;&#24341; (5)</span>
print<span class="br0">(</span><span class="st0">&quot;s7&quot;</span>, sizeof s7, s7.<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">
name &#9474; sizeof &#9474; extent
&#9472;&#9472;&#9472;&#9472;&#9472;&#9532;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9532;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;&#9472;
s1 &#9474; 16 &#9474; dynamic
s2 &#9474; 16 &#9474; dynamic
s3 &#9474; 8 &#9474; 5
s4 &#9474; 16 &#9474; dynamic
s5 &#9474; 8 &#9474; 3
s6 &#9474; 8 &#9474; 3
s7 &#9474; 16 &#9474; dynamic</pre></div>
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