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<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Go by Example 中文版: 切片</title>
<link rel=stylesheet href="site.css">
</head>
<script>
onkeydown = (e) => {
if (e.key == "ArrowLeft") {
window.location.href = 'arrays';
}
if (e.key == "ArrowRight") {
window.location.href = 'maps';
}
}
</script>
<body>
<div class="example" id="slices">
<h2><a href="./">Go by Example 中文版</a>: 切片</h2>
<table>
<tr>
<td class="docs">
<p><em>Slice</em> 是 Go 中一个重要的数据类型，它提供了比数组更强大的序列交互方式。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<a href="https://play.studygolang.com/p/qC32TQNNUoC"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kn">import</span> <span class="s">"fmt"</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
</td>
<td class="code leading">
<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>与数组不同，slice 的类型仅由它所包含的元素的类型决定（与元素个数无关）。
要创建一个长度不为 0 的空 slice，需要使用内建函数 <code>make</code>。
这里我们创建了一个长度为 3 的 <code>string</code> 类型的 slice（初始值为零值）。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">s</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([]</span><span class="kt">string</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"emp:"</span><span class="p">,</span> <span class="nx">s</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>我们可以和数组一样设置和得到值</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">s</span><span class="p">[</span><span class="mi">0</span><span class="p">]</span> <span class="p">=</span> <span class="s">"a"</span>
<span class="nx">s</span><span class="p">[</span><span class="mi">1</span><span class="p">]</span> <span class="p">=</span> <span class="s">"b"</span>
<span class="nx">s</span><span class="p">[</span><span class="mi">2</span><span class="p">]</span> <span class="p">=</span> <span class="s">"c"</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"set:"</span><span class="p">,</span> <span class="nx">s</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"get:"</span><span class="p">,</span> <span class="nx">s</span><span class="p">[</span><span class="mi">2</span><span class="p">])</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p><code>len</code> 返回 slice 的长度</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"len:"</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">s</span><span class="p">))</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>除了基本操作外，slice 支持比数组更丰富的操作。比如 slice 支持内建函数 <code>append</code>，
该函数会返回一个包含了一个或者多个新值的 slice。
注意由于 <code>append</code> 可能返回一个新的 slice，我们需要接收其返回值。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">s</span> <span class="p">=</span> <span class="nb">append</span><span class="p">(</span><span class="nx">s</span><span class="p">,</span> <span class="s">"d"</span><span class="p">)</span>
<span class="nx">s</span> <span class="p">=</span> <span class="nb">append</span><span class="p">(</span><span class="nx">s</span><span class="p">,</span> <span class="s">"e"</span><span class="p">,</span> <span class="s">"f"</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"apd:"</span><span class="p">,</span> <span class="nx">s</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>slice 还可以 <code>copy</code>。这里我们创建一个空的和 <code>s</code> 有相同长度的 slice——<code>c</code>，
然后将 <code>s</code> 复制给 <code>c</code>。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">c</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([]</span><span class="kt">string</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="nx">s</span><span class="p">))</span>
<span class="nb">copy</span><span class="p">(</span><span class="nx">c</span><span class="p">,</span> <span class="nx">s</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"cpy:"</span><span class="p">,</span> <span class="nx">c</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>slice 支持通过 <code>slice[low:high]</code> 语法进行“切片”操作。
例如，右边的操作可以得到一个包含元素 <code>s[2]</code>、<code>s[3]</code> 和 <code>s[4]</code> 的 slice。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">l</span> <span class="o">:=</span> <span class="nx">s</span><span class="p">[</span><span class="mi">2</span><span class="p">:</span><span class="mi">5</span><span class="p">]</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"sl1:"</span><span class="p">,</span> <span class="nx">l</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>这个 slice 包含从 <code>s[0]</code> 到 <code>s[5]</code>（不包含 5）的元素。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">l</span> <span class="p">=</span> <span class="nx">s</span><span class="p">[:</span><span class="mi">5</span><span class="p">]</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"sl2:"</span><span class="p">,</span> <span class="nx">l</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>这个 slice 包含从 <code>s[2]</code>（包含 2）之后的元素。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">l</span> <span class="p">=</span> <span class="nx">s</span><span class="p">[</span><span class="mi">2</span><span class="p">:]</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"sl3:"</span><span class="p">,</span> <span class="nx">l</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>我们可以在一行代码中声明并初始化一个 slice 变量。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="nx">t</span> <span class="o">:=</span> <span class="p">[]</span><span class="kt">string</span><span class="p">{</span><span class="s">"g"</span><span class="p">,</span> <span class="s">"h"</span><span class="p">,</span> <span class="s">"i"</span><span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"dcl:"</span><span class="p">,</span> <span class="nx">t</span><span class="p">)</span>
</pre>
</td>
</tr>
<tr>
<td class="docs">
<p>Slice 可以组成多维数据结构。内部的 slice 长度可以不一致，这一点和多维数组不同。</p>
</td>
<td class="code">
<pre class="chroma">
<span class="nx">twoD</span> <span class="o">:=</span> <span class="nb">make</span><span class="p">([][]</span><span class="kt">int</span><span class="p">,</span> <span class="mi">3</span><span class="p">)</span>
<span class="k">for</span> <span class="nx">i</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">i</span> <span class="p"><</span> <span class="mi">3</span><span class="p">;</span> <span class="nx">i</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">innerLen</span> <span class="o">:=</span> <span class="nx">i</span> <span class="o">+</span> <span class="mi">1</span>
<span class="nx">twoD</span><span class="p">[</span><span class="nx">i</span><span class="p">]</span> <span class="p">=</span> <span class="nb">make</span><span class="p">([]</span><span class="kt">int</span><span class="p">,</span> <span class="nx">innerLen</span><span class="p">)</span>
<span class="k">for</span> <span class="nx">j</span> <span class="o">:=</span> <span class="mi">0</span><span class="p">;</span> <span class="nx">j</span> <span class="p"><</span> <span class="nx">innerLen</span><span class="p">;</span> <span class="nx">j</span><span class="o">++</span> <span class="p">{</span>
<span class="nx">twoD</span><span class="p">[</span><span class="nx">i</span><span class="p">][</span><span class="nx">j</span><span class="p">]</span> <span class="p">=</span> <span class="nx">i</span> <span class="o">+</span> <span class="nx">j</span>
<span class="p">}</span>
<span class="p">}</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="s">"2d: "</span><span class="p">,</span> <span class="nx">twoD</span><span class="p">)</span>
<span class="p">}</span>
</pre>
</td>
</tr>
</table>
<table>
<tr>
<td class="docs">
<p>注意，slice 和数组是不同的类型，但它们通过 <code>fmt.Println</code> 打印的输出结果是类似的。</p>
</td>
<td class="code leading">
<pre class="chroma">
<span class="gp">$</span> go run slices.go
<span class="go">emp: [ ]
</span><span class="go">set: [a b c]
</span><span class="go">get: c
</span><span class="go">len: 3
</span><span class="go">apd: [a b c d e f]
</span><span class="go">cpy: [a b c d e f]
</span><span class="go">sl1: [c d e]
</span><span class="go">sl2: [a b c d e]
</span><span class="go">sl3: [c d e f]
</span><span class="go">dcl: [g h i]
</span><span class="go">2d: [[0] [1 2] [2 3 4]]</span></pre>
</td>
</tr>
<tr>
<td class="docs">
<p>看看这个由 Go 团队撰写的一篇<a href="http://blog.golang.org/2011/01/go-slices-usage-and-internals.html">很棒的博文</a>，了解更多关于 Go 中 slice 的设计和实现细节。</p>
</td>
<td class="code empty leading">
</td>
</tr>
<tr>
<td class="docs">
<p>现在，我们已经学习了数组和 slice，接下来我们将学习 Go 中的另一个重要的内建数据类型：map。</p>
</td>
<td class="code empty">
</td>
</tr>
</table>
<p class="next">
下一个例子: <a href="maps">Map</a>
</p>
<p class="footer">
<a href="https://twitter.com/mmcgrana">@mmcgrana</a> 和<a href="https://eli.thegreenplace.net">Eli Bendersky</a>编写 | <a href="https://github.com/gobyexample-cn">gobyexample-cn</a> 翻译 | <a href="https://github.com/gobyexample-cn/gobyexample/issues">反馈</a> | <a href="https://github.com/gobyexample-cn/gobyexample">源码</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a> </p>
</p>
</div>
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