268 lines
10 KiB
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Generated
268 lines
10 KiB
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Generated
<!DOCTYPE html>
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<meta charset="utf-8">
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<title>Go by Example: Number Parsing</title>
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<div class="example" id="number-parsing">
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<h2><a href="./">Go by Example</a>: Number Parsing</h2>
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<table>
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<tr>
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<td class="docs">
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<p>Parsing numbers from strings is a basic but common task
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in many programs; here’s how to do it in Go.</p>
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</td>
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<td class="code empty leading">
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<a href="https://go.dev/play/p/ZAMEid6Fpmu"><img title="Run code" src="play.png" class="run" /></a><img title="Copy code" src="clipboard.png" class="copy" />
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<pre class="chroma"><span class="kn">package</span> <span class="nx">main</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>The built-in package <code>strconv</code> provides the number
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parsing.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="kn">import</span> <span class="p">(</span>
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<span class="s">"fmt"</span>
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<span class="s">"strconv"</span>
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<span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="kd">func</span> <span class="nf">main</span><span class="p">()</span> <span class="p">{</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>With <code>ParseFloat</code>, this <code>64</code> tells how many bits of
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precision to parse.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">f</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nf">ParseFloat</span><span class="p">(</span><span class="s">"1.234"</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">f</span><span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>For <code>ParseInt</code>, the <code>0</code> means infer the base from
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the string. <code>64</code> requires that the result fit in 64
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bits.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">i</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nf">ParseInt</span><span class="p">(</span><span class="s">"123"</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">i</span><span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p><code>ParseInt</code> will recognize hex-formatted numbers.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">d</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nf">ParseInt</span><span class="p">(</span><span class="s">"0x1c8"</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">d</span><span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>A <code>ParseUint</code> is also available.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">u</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nf">ParseUint</span><span class="p">(</span><span class="s">"789"</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">u</span><span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p><code>Atoi</code> is a convenience function for basic base-10
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<code>int</code> parsing.</p>
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</td>
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<td class="code leading">
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<pre class="chroma">
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<span class="nx">k</span><span class="p">,</span> <span class="nx">_</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nf">Atoi</span><span class="p">(</span><span class="s">"135"</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">k</span><span class="p">)</span>
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</pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Parse functions return an error on bad input.</p>
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</td>
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<td class="code">
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<pre class="chroma">
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<span class="nx">_</span><span class="p">,</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">strconv</span><span class="p">.</span><span class="nf">Atoi</span><span class="p">(</span><span class="s">"wat"</span><span class="p">)</span>
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<span class="nx">fmt</span><span class="p">.</span><span class="nf">Println</span><span class="p">(</span><span class="nx">e</span><span class="p">)</span>
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<span class="p">}</span>
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</pre>
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</td>
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</tr>
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</table>
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<table>
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<tr>
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<td class="docs">
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</td>
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<td class="code leading">
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<pre class="chroma"><span class="gp">$</span> go run number-parsing.go
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<span class="go">1.234
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</span><span class="go">123
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</span><span class="go">456
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</span><span class="go">789
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</span><span class="go">135
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</span><span class="go">strconv.ParseInt: parsing "wat": invalid syntax</span></pre>
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</td>
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</tr>
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<tr>
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<td class="docs">
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<p>Next we’ll look at another common parsing task: URLs.</p>
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</td>
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<td class="code empty">
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</td>
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</tr>
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</table>
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<p class="next">
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Next example: <a href="url-parsing">URL Parsing</a>.
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</p>
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by <a href="https://markmcgranaghan.com">Mark McGranaghan</a> and <a href="https://eli.thegreenplace.net">Eli Bendersky</a> | <a href="https://github.com/mmcgrana/gobyexample">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a> | <button id="theme-button">Toggle theme</button>
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