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gobyexample/public/string-functions
Mark McGranaghan cca7879dce Add note about len and [] operating on bytes 
Fixes #148.
2016-12-27 07:41:08 -08:00

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<title>Go by Example: String Functions</title>
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<div class="example" id="string-functions">
<h2><a href="./">Go by Example</a>: String Functions</h2>
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<p>The standard library&rsquo;s <code>strings</code> package provides many
useful string-related functions. Here are some examples
to give you a sense of the package.</p>
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<a href="http://play.golang.org/p/Lf5_Zbg6or"><img title="Run code" src="play.png" class="run" /></a>
<div class="highlight"><pre><span class="kn">package</span> <span class="nx">main</span>
</pre></div>
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<div class="highlight"><pre><span class="kn">import</span> <span class="nx">s</span> <span class="s">&quot;strings&quot;</span>
<span class="kn">import</span> <span class="s">&quot;fmt&quot;</span>
</pre></div>
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<p>We alias <code>fmt.Println</code> to a shorter name as we&rsquo;ll use
it a lot below.</p>
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<div class="highlight"><pre><span class="kd">var</span> <span class="nx">p</span> <span class="p">=</span> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span>
</pre></div>
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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>
</pre></div>
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<p>Here&rsquo;s a sample of the functions available in
<code>strings</code>. Since these are functions from the
package, not methods on the string object itself,
we need pass the string in question as the first
argument to the function. You can find more
functions in the <a href="http://golang.org/pkg/strings/"><code>strings</code></a>
package docs.</p>
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<div class="highlight"><pre> <span class="nx">p</span><span class="p">(</span><span class="s">&quot;Contains: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">Contains</span><span class="p">(</span><span class="s">&quot;test&quot;</span><span class="p">,</span> <span class="s">&quot;es&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;Count: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">Count</span><span class="p">(</span><span class="s">&quot;test&quot;</span><span class="p">,</span> <span class="s">&quot;t&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;HasPrefix: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">HasPrefix</span><span class="p">(</span><span class="s">&quot;test&quot;</span><span class="p">,</span> <span class="s">&quot;te&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;HasSuffix: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">HasSuffix</span><span class="p">(</span><span class="s">&quot;test&quot;</span><span class="p">,</span> <span class="s">&quot;st&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;Index: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">Index</span><span class="p">(</span><span class="s">&quot;test&quot;</span><span class="p">,</span> <span class="s">&quot;e&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;Join: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">Join</span><span class="p">([]</span><span class="kt">string</span><span class="p">{</span><span class="s">&quot;a&quot;</span><span class="p">,</span> <span class="s">&quot;b&quot;</span><span class="p">},</span> <span class="s">&quot;-&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;Repeat: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">Repeat</span><span class="p">(</span><span class="s">&quot;a&quot;</span><span class="p">,</span> <span class="mi">5</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;Replace: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">Replace</span><span class="p">(</span><span class="s">&quot;foo&quot;</span><span class="p">,</span> <span class="s">&quot;o&quot;</span><span class="p">,</span> <span class="s">&quot;0&quot;</span><span class="p">,</span> <span class="o">-</span><span class="mi">1</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;Replace: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">Replace</span><span class="p">(</span><span class="s">&quot;foo&quot;</span><span class="p">,</span> <span class="s">&quot;o&quot;</span><span class="p">,</span> <span class="s">&quot;0&quot;</span><span class="p">,</span> <span class="mi">1</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;Split: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">Split</span><span class="p">(</span><span class="s">&quot;a-b-c-d-e&quot;</span><span class="p">,</span> <span class="s">&quot;-&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;ToLower: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">ToLower</span><span class="p">(</span><span class="s">&quot;TEST&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;ToUpper: &quot;</span><span class="p">,</span> <span class="nx">s</span><span class="p">.</span><span class="nx">ToUpper</span><span class="p">(</span><span class="s">&quot;test&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">()</span>
</pre></div>
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<p>Not part of <code>strings</code>, but worth mentioning here, are
the mechanisms for getting the length of a string in
bytes and getting a byte by index.</p>
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<td class="code leading">
<div class="highlight"><pre> <span class="nx">p</span><span class="p">(</span><span class="s">&quot;Len: &quot;</span><span class="p">,</span> <span class="nb">len</span><span class="p">(</span><span class="s">&quot;hello&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="s">&quot;Char:&quot;</span><span class="p">,</span> <span class="s">&quot;hello&quot;</span><span class="p">[</span><span class="mi">1</span><span class="p">])</span>
<span class="p">}</span>
</pre></div>
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<td class="docs">
<p>Note that <code>len</code> and indexing above work at the byte level.
Go uses UTF-8 encoded strings, so this is often useful
as-is. If you&rsquo;re working with potentially multi-byte
characters you&rsquo;ll want to use encoding-aware operations.
See <a href="https://blog.golang.org/strings">strings, bytes, runes and characters in Go</a>
for more information.</p>
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<div class="highlight"><pre><span class="gp">$</span> go run string-functions.go
<span class="go">Contains: true</span>
<span class="go">Count: 2</span>
<span class="go">HasPrefix: true</span>
<span class="go">HasSuffix: true</span>
<span class="go">Index: 1</span>
<span class="go">Join: a-b</span>
<span class="go">Repeat: aaaaa</span>
<span class="go">Replace: f00</span>
<span class="go">Replace: f0o</span>
<span class="go">Split: [a b c d e]</span>
<span class="go">ToLower: test</span>
<span class="go">ToUpper: TEST</span>
</pre></div>
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<div class="highlight"><pre><span class="go">Len: 5</span>
<span class="go">Char: 101</span>
</pre></div>
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<p class="next">
Next example: <a href="string-formatting">String Formatting</a>.
</p>
<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/string-functions">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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