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<title>Go by Example: Number Parsing</title>
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<div class="example" id="number-parsing">
<h2><a href="./">Go by Example</a>: Number Parsing</h2>
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<p>Parsing numbers from strings is a basic but common task
in many programs; here&rsquo;s how to do it in Go.</p>
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<a href="http://play.golang.org/p/N90EppECFk"><img title="Run code" src="play.png" class="run" /></a>
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
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<p>The built-in package <code>strconv</code> provides the number
parsing.</p>
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<div class="highlight"><pre><span class="kn">import</span> <span class="s">&quot;strconv&quot;</span>
<span class="kn">import</span> <span class="s">&quot;fmt&quot;</span>
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<div class="highlight"><pre><span class="kd">func</span> <span class="nx">main</span><span class="p">()</span> <span class="p">{</span>
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<p>With <code>ParseFloat</code>, this <code>64</code> tells how many bits of
precision to parse.</p>
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<div class="highlight"><pre> <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="nx">ParseFloat</span><span class="p">(</span><span class="s">&quot;1.234&quot;</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">f</span><span class="p">)</span>
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<p>For <code>ParseInt</code>, the <code>0</code> means infer the base from
the string. <code>64</code> requires that the result fit in 64
bits.</p>
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<div class="highlight"><pre> <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="nx">ParseInt</span><span class="p">(</span><span class="s">&quot;123&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">i</span><span class="p">)</span>
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<p><code>ParseInt</code> will recognize hex-formatted numbers.</p>
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<div class="highlight"><pre> <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="nx">ParseInt</span><span class="p">(</span><span class="s">&quot;0x1c8&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">d</span><span class="p">)</span>
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<p>A <code>ParseUint</code> is also available.</p>
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<div class="highlight"><pre> <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="nx">ParseUint</span><span class="p">(</span><span class="s">&quot;789&quot;</span><span class="p">,</span> <span class="mi">0</span><span class="p">,</span> <span class="mi">64</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">u</span><span class="p">)</span>
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<p><code>Atoi</code> is a convenience function for basic base-10
<code>int</code> parsing.</p>
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<div class="highlight"><pre> <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="nx">Atoi</span><span class="p">(</span><span class="s">&quot;135&quot;</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">k</span><span class="p">)</span>
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<p>Parse functions return an error on bad input.</p>
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<div class="highlight"><pre> <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="nx">Atoi</span><span class="p">(</span><span class="s">&quot;wat&quot;</span><span class="p">)</span>
<span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span><span class="p">(</span><span class="nx">e</span><span class="p">)</span>
<span class="p">}</span>
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<div class="highlight"><pre><span class="gp">$</span> go run number-parsing.go
<span class="go">1.234</span>
<span class="go">123</span>
<span class="go">456</span>
<span class="go">789</span>
<span class="go">135</span>
<span class="go">strconv.ParseInt: parsing &quot;wat&quot;: invalid syntax</span>
</pre></div>
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<p>Next we&rsquo;ll look at another common parsing task: URLs.</p>
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Next example: <a href="url-parsing">URL Parsing</a>.
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<p class="footer">
by <a href="https://twitter.com/mmcgrana">@mmcgrana</a> | <a href="mailto:mmcgrana@gmail.com">feedback</a> | <a href="https://github.com/mmcgrana/gobyexample/blob/master/examples/number-parsing">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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