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<title>std::map&lt;Key,T,Compare,Allocator&gt;::begin, std::map&lt;Key,T,Compare,Allocator&gt;::cbegin</title>
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<h1 id="firstHeading" class="firstHeading"><span style="font-size:0.7em; line-height:130%">std::map&lt;Key,T,Compare,Allocator&gt;::</span>begin, <span style="font-size:0.7em; line-height:130%">std::map&lt;Key,T,Compare,Allocator&gt;::</span>cbegin</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-map.html">map</a></span></div>
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<div><span class="mw-geshi cpp source-cpp">iterator begin<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-until-cxx11">(C++11 &#21069;)</span></td>
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<div><span class="mw-geshi cpp source-cpp">iterator begin<span class="br0">(</span><span class="br0">)</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp">const_iterator begin<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-until-cxx11">(C++11 &#21069;)</span></td>
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<div><span class="mw-geshi cpp source-cpp">const_iterator begin<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 &#36215;)</span></td>
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<div><span class="mw-geshi cpp source-cpp">const_iterator cbegin<span class="br0">(</span><span class="br0">)</span> <span class="kw4">const</span> <span class="kw1">noexcept</span><span class="sy4">;</span></span></div>
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<td><span class="t-mark-rev t-since-cxx11">(C++11 &#36215;)</span></td>
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<p>&#36820;&#22238;&#25351;&#21521; <code>map</code> &#39318;&#20803;&#32032;&#30340;&#36845;&#20195;&#22120;&#12290;</p>
<p>&#33509; <code>map</code> &#20026;&#31354;&#65292;&#21017;&#36820;&#22238;&#30340;&#36845;&#20195;&#22120;&#23558;&#31561;&#20110; <span class="t-lc"><a href="cpp-container-map-end.html">end()</a></span> &#12290;</p>
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<p><img alt="range-begin-end.svg" src="range-begin-end.svg" width="546" height="157" /></p>
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<h3><span class="mw-headline" id=".E5.8F.82.E6.95.B0">&#21442;&#25968;</span></h3>
<p>&#65288;&#26080;&#65289;</p>
<h3><span class="mw-headline" id=".E8.BF.94.E5.9B.9E.E5.80.BC">&#36820;&#22238;&#20540;</span></h3>
<p>&#25351;&#21521;&#39318;&#20803;&#32032;&#30340;&#36845;&#20195;&#22120;&#12290;</p>
<h3><span class="mw-headline" id=".E5.A4.8D.E6.9D.82.E5.BA.A6">&#22797;&#26434;&#24230;</span></h3>
<p>&#24120;&#25968;&#12290;</p>
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<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;iostream&gt;</span>
<span class="co2">#include &lt;map&gt;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
<a href="cpp-container-map.html"><span class="kw1281">std::<span class="me2">map</span></span></a><span class="sy1">&lt;</span><span class="kw4">int</span>, <span class="kw4">float</span><span class="sy1">&gt;</span> num_map<span class="sy4">;</span>
num_map<span class="br0">[</span><span class="nu0">4</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu16">4.13</span><span class="sy4">;</span>
num_map<span class="br0">[</span><span class="nu0">9</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu16">9.24</span><span class="sy4">;</span>
num_map<span class="br0">[</span><span class="nu0">1</span><span class="br0">]</span> <span class="sy1">=</span> <span class="nu16">1.09</span><span class="sy4">;</span>
<span class="co1">// &#35843;&#29992; a_map.begin() &#19982; a_map.end()</span>
<span class="kw1">for</span> <span class="br0">(</span><span class="kw4">auto</span> it <span class="sy1">=</span> num_map.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> it <span class="sy3">!</span><span class="sy1">=</span> num_map.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="sy2">++</span>it<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> it<span class="sy2">-</span><span class="sy1">&gt;</span>first <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;, &quot;</span> <span class="sy1">&lt;&lt;</span> it<span class="sy2">-</span><span class="sy1">&gt;</span>second <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></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<pre class="de1">1, 1.09
4, 4.13
9, 9.24</pre></div>
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<h4><span class="mw-headline" id=".E4.BD.BF.E7.94.A8.E5.AE.9A.E5.88.B6.E6.AF.94.E8.BE.83.E5.87.BD.E6.95.B0.E7.9A.84.E7.A4.BA.E4.BE.8B">&#20351;&#29992;&#23450;&#21046;&#27604;&#36739;&#20989;&#25968;&#30340;&#31034;&#20363;</span></h4>
<div class="t-example">
<div class="t-example-live-link"></div>
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<div class="cpp source-cpp">
<pre class="de1"><span class="co2">#include &lt;cmath&gt;</span>
<span class="co2">#include &lt;iostream&gt;</span>
<span class="co2">#include &lt;map&gt;</span>
<span class="kw1">struct</span> Point <span class="br0">{</span> <span class="kw4">double</span> x, y<span class="sy4">;</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="co1">// &#27604;&#36739;&#20108;&#20010; Pointer &#25351;&#38024;&#30340; x &#22352;&#26631;</span>
<span class="kw1">struct</span> PointCmp <span class="br0">{</span>
<span class="kw4">bool</span> operator<span class="br0">(</span><span class="br0">)</span><span class="br0">(</span><span class="kw4">const</span> Point <span class="sy2">*</span>lhs, <span class="kw4">const</span> Point <span class="sy2">*</span>rhs<span class="br0">)</span> <span class="kw4">const</span> <span class="br0">{</span>
<span class="kw1">return</span> lhs<span class="sy2">-</span><span class="sy1">&gt;</span>x <span class="sy1">&lt;</span> rhs<span class="sy2">-</span><span class="sy1">&gt;</span>x<span class="sy4">;</span>
<span class="br0">}</span>
<span class="br0">}</span><span class="sy4">;</span>
<span class="kw4">int</span> main<span class="br0">(</span><span class="br0">)</span> <span class="br0">{</span>
<span class="co1">// &#27880;&#24847;&#23613;&#31649; x &#22352;&#26631;&#20081;&#24207;&#65292;&#20134;&#23558;&#25353;&#29031;&#36882;&#22686;&#30340; x &#22352;&#26631;&#36845;&#20195; map</span>
Point points<span class="br0">[</span><span class="nu0">3</span><span class="br0">]</span> <span class="sy1">=</span> <span class="br0">{</span> <span class="br0">{</span><span class="nu0">2</span>, <span class="nu0">0</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">1</span>, <span class="nu0">0</span><span class="br0">}</span>, <span class="br0">{</span><span class="nu0">3</span>, <span class="nu0">0</span><span class="br0">}</span> <span class="br0">}</span><span class="sy4">;</span>
<span class="co1">// mag &#26159;&#21457;&#36865;&#32467;&#28857;&#22320;&#22336;&#21040;&#20854;&#22312; x-y &#24179;&#38754;&#20013;&#38271;&#24230;&#30340; map</span>
<span class="co1">// &#23613;&#31649;&#38190;&#20026;&#25351;&#21521; Point &#30340;&#25351;&#38024;&#65292;&#25105;&#20204;&#24076;&#26395;&#25353;&#29031;&#28857;&#30340; x &#22352;&#26631;&#32780;&#38750;&#28857;&#30340;&#22320;&#22336;&#20026; map &#36171;&#24207;&#12290;</span>
<span class="co1">// &#36890;&#36807;&#29992; PointCmp &#31867;&#30340;&#27604;&#36739;&#26041;&#27861;&#36827;&#34892;&#12290;</span>
<a href="cpp-container-map.html"><span class="kw1281">std::<span class="me2">map</span></span></a><span class="sy1">&lt;</span>Point <span class="sy2">*</span>, <span class="kw4">double</span>, PointCmp<span class="sy1">&gt;</span> mag<span class="br0">(</span><span class="br0">{</span>
<span class="br0">{</span> points, <span class="nu0">2</span> <span class="br0">}</span>,
<span class="br0">{</span> points <span class="sy2">+</span> <span class="nu0">1</span>, <span class="nu0">1</span> <span class="br0">}</span>,
<span class="br0">{</span> points <span class="sy2">+</span> <span class="nu0">2</span>, <span class="nu0">3</span> <span class="br0">}</span>
<span class="br0">}</span><span class="br0">)</span><span class="sy4">;</span>
<span class="co1">// &#20174; 0 &#21040;&#38271;&#24230;&#26356;&#25913;&#27599;&#20010; y &#22352;&#26631;</span>
<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> iter <span class="sy1">=</span> mag.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> iter <span class="sy3">!</span><span class="sy1">=</span> mag.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="sy2">++</span>iter<span class="br0">)</span><span class="br0">{</span>
<span class="kw4">auto</span> cur <span class="sy1">=</span> iter<span class="sy2">-</span><span class="sy1">&gt;</span>first<span class="sy4">;</span> <span class="co1">// &#25351;&#21521; Point &#30340;&#25351;&#38024;</span>
cur<span class="sy2">-</span><span class="sy1">&gt;</span>y <span class="sy1">=</span> mag<span class="br0">[</span>cur<span class="br0">]</span><span class="sy4">;</span> <span class="co1">// &#20134;&#33021;&#29992; cur-&gt;y = iter-&gt;second;</span>
<span class="br0">}</span>
<span class="co1">// &#26356;&#26032;&#24182;&#25171;&#21360;&#27599;&#20010;&#28857;&#30340;&#38271;&#24230;</span>
<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> iter <span class="sy1">=</span> mag.<span class="me1">begin</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> iter <span class="sy3">!</span><span class="sy1">=</span> mag.<span class="me1">end</span><span class="br0">(</span><span class="br0">)</span><span class="sy4">;</span> <span class="sy2">++</span>iter<span class="br0">)</span><span class="br0">{</span>
<span class="kw4">auto</span> cur <span class="sy1">=</span> iter<span class="sy2">-</span><span class="sy1">&gt;</span>first<span class="sy4">;</span>
mag<span class="br0">[</span>cur<span class="br0">]</span> <span class="sy1">=</span> <a href="cpp-numeric-math-hypot.html"><span class="kw1331">std::<span class="me2">hypot</span></span></a><span class="br0">(</span>cur<span class="sy2">-</span><span class="sy1">&gt;</span>x, cur<span class="sy2">-</span><span class="sy1">&gt;</span>y<span class="br0">)</span><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">&quot;The magnitude of (&quot;</span> <span class="sy1">&lt;&lt;</span> cur<span class="sy2">-</span><span class="sy1">&gt;</span>x <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;, &quot;</span> <span class="sy1">&lt;&lt;</span> cur<span class="sy2">-</span><span class="sy1">&gt;</span>y <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;) is &quot;</span><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> iter<span class="sy2">-</span><span class="sy1">&gt;</span>second <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="co1">// &#20197;&#22522;&#20110;&#33539;&#22260;&#30340; for &#24490;&#29615;&#37325;&#22797;&#19978;&#36848;&#20869;&#23481;</span>
<span class="kw1">for</span><span class="br0">(</span><span class="kw4">auto</span> i <span class="sy4">:</span> mag<span class="br0">)</span> <span class="br0">{</span>
<span class="kw4">auto</span> cur <span class="sy1">=</span> i.<span class="me1">first</span><span class="sy4">;</span>
cur<span class="sy2">-</span><span class="sy1">&gt;</span>y <span class="sy1">=</span> i.<span class="me1">second</span><span class="sy4">;</span>
mag<span class="br0">[</span>cur<span class="br0">]</span> <span class="sy1">=</span> <a href="cpp-numeric-math-hypot.html"><span class="kw1331">std::<span class="me2">hypot</span></span></a><span class="br0">(</span>cur<span class="sy2">-</span><span class="sy1">&gt;</span>x, cur<span class="sy2">-</span><span class="sy1">&gt;</span>y<span class="br0">)</span><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">&quot;The magnitude of (&quot;</span> <span class="sy1">&lt;&lt;</span> cur<span class="sy2">-</span><span class="sy1">&gt;</span>x <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;, &quot;</span> <span class="sy1">&lt;&lt;</span> cur<span class="sy2">-</span><span class="sy1">&gt;</span>y <span class="sy1">&lt;&lt;</span> <span class="st0">&quot;) is &quot;</span><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> mag<span class="br0">[</span>cur<span class="br0">]</span> <span class="sy1">&lt;&lt;</span> <span class="st0">&#39;<span class="es1">\n</span>&#39;</span><span class="sy4">;</span>
<span class="co1">// &#27880;&#24847;&#19982;&#19978;&#36848; std::cout &lt;&lt; iter-&gt;second &lt;&lt; &#39;\n&#39;; &#30456;&#21453;&#65292;</span>
<span class="co1">// std::cout &lt;&lt; i.second &lt;&lt; &#39;\n&#39;; &#23558;&#19981;&#25171;&#21360;&#26356;&#26032;&#30340;&#38271;&#24230;</span>
<span class="br0">}</span>
<span class="br0">}</span></pre></div>
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<p>&#36755;&#20986;&#65306;</p>
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<div class="text source-text">
<pre class="de1">The magnitude of (1, 1) is 1.41421
The magnitude of (2, 2) is 2.82843
The magnitude of (3, 3) is 4.24264
The magnitude of (1, 1.41421) is 1.73205
The magnitude of (2, 2.82843) is 3.4641
The magnitude of (3, 4.24264) is 5.19615</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><a href="cpp-container-map-end.html"><span class="t-lines"><span>end</span> <span>cend</span></span></a></div>
<div><span class="t-lines"><span></span><span><span class="t-mark-rev t-since-cxx11">(C++11)</span></span></span></div>
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<td>&#36820;&#22238;&#25351;&#21521;&#26411;&#23614;&#30340;&#36845;&#20195;&#22120;<br />
<span class="t-mark">(&#20844;&#24320;&#25104;&#21592;&#20989;&#25968;)</span></td>
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