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gobyexample/public/time-formatting-parsing
Mark McGranaghan a8ee83af78 Emphasize time constants 
In most cases users will format and parse times using the constants
provided in package time. Show these first before getting into custom
example-based formats.
2014-04-15 18:09:28 -07:00

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<title>Go by Example: Time Formatting / Parsing</title>
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<div class="example" id="time-formatting-parsing">
<h2><a href="./">Go by Example</a>: Time Formatting / Parsing</h2>
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<p>Go supports time formatting and parsing via
pattern-based layouts.</p>
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<a href="http://play.golang.org/p/siwR2J2ke0"><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="s">&quot;fmt&quot;</span>
<span class="kn">import</span> <span class="s">&quot;time&quot;</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>
<span class="nx">p</span> <span class="o">:=</span> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Println</span>
</pre></div>
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<p>Here&rsquo;s a basic example of formatting a time
according to RFC3339, using the corresponding format
constant.</p>
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<div class="highlight"><pre> <span class="nx">t</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Now</span><span class="p">()</span>
<span class="nx">p</span><span class="p">(</span><span class="nx">t</span><span class="p">.</span><span class="nx">Format</span><span class="p">(</span><span class="nx">time</span><span class="p">.</span><span class="nx">RFC3339</span><span class="p">))</span>
</pre></div>
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<p>Time parsing uses the same format values as <code>Format</code>
does.</p>
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<div class="highlight"><pre> <span class="nx">t1</span><span class="p">,</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Parse</span><span class="p">(</span>
<span class="nx">time</span><span class="p">.</span><span class="nx">RFC3339</span><span class="p">,</span>
<span class="s">&quot;2012-11-01T22:08:41+00:00&quot;</span><span class="p">)</span>
<span class="nx">p</span><span class="p">(</span><span class="nx">t1</span><span class="p">)</span>
</pre></div>
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<p><code>Format</code> and <code>Parse</code> uses example-based formats. They
take a formatted version of the reference time
<code>Mon Jan 2 15:04:05 MST 2006</code> to determine the
general pattern with which to format/parse the given
time/string. The example time must be exactly as shown:
the year 2006, 15 for the hour, Monday for the day of
the week, etc. Usually you&rsquo;ll use a constant from
<code>time</code> for these formats, but you can also supply
custom formats.</p>
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<div class="highlight"><pre> <span class="nx">p</span><span class="p">(</span><span class="nx">t</span><span class="p">.</span><span class="nx">Format</span><span class="p">(</span><span class="s">&quot;3:04PM&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="nx">t</span><span class="p">.</span><span class="nx">Format</span><span class="p">(</span><span class="s">&quot;Mon Jan _2 15:04:05 2006&quot;</span><span class="p">))</span>
<span class="nx">p</span><span class="p">(</span><span class="nx">t</span><span class="p">.</span><span class="nx">Format</span><span class="p">(</span><span class="s">&quot;2006-01-02T15:04:05.999999-07:00&quot;</span><span class="p">))</span>
<span class="nx">form</span> <span class="o">:=</span> <span class="s">&quot;3 04 PM&quot;</span>
<span class="nx">t2</span><span class="p">,</span> <span class="nx">e</span> <span class="o">:=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Parse</span><span class="p">(</span><span class="nx">form</span><span class="p">,</span> <span class="s">&quot;8 41 PM&quot;</span><span class="p">)</span>
<span class="nx">p</span><span class="p">(</span><span class="nx">t2</span><span class="p">)</span>
</pre></div>
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<p>For purely numeric representations you can also
use standard string formatting with the extracted
components of the time value.</p>
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<div class="highlight"><pre> <span class="nx">fmt</span><span class="p">.</span><span class="nx">Printf</span><span class="p">(</span><span class="s">&quot;%d-%02d-%02dT%02d:%02d:%02d-00:00\n&quot;</span><span class="p">,</span>
<span class="nx">t</span><span class="p">.</span><span class="nx">Year</span><span class="p">(),</span> <span class="nx">t</span><span class="p">.</span><span class="nx">Month</span><span class="p">(),</span> <span class="nx">t</span><span class="p">.</span><span class="nx">Day</span><span class="p">(),</span>
<span class="nx">t</span><span class="p">.</span><span class="nx">Hour</span><span class="p">(),</span> <span class="nx">t</span><span class="p">.</span><span class="nx">Minute</span><span class="p">(),</span> <span class="nx">t</span><span class="p">.</span><span class="nx">Second</span><span class="p">())</span>
</pre></div>
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<p><code>Parse</code> will return an error on malformed input
explaining the parsing problem.</p>
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<div class="highlight"><pre> <span class="nx">ansic</span> <span class="o">:=</span> <span class="s">&quot;Mon Jan _2 15:04:05 2006&quot;</span>
<span class="nx">_</span><span class="p">,</span> <span class="nx">e</span> <span class="p">=</span> <span class="nx">time</span><span class="p">.</span><span class="nx">Parse</span><span class="p">(</span><span class="nx">ansic</span><span class="p">,</span> <span class="s">&quot;8:41PM&quot;</span><span class="p">)</span>
<span class="nx">p</span><span class="p">(</span><span class="nx">e</span><span class="p">)</span>
<span class="p">}</span>
</pre></div>
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<div class="highlight"><pre><span class="gp">$</span> go run <span class="nb">time</span>-formatting-parsing.go
<span class="go">2014-04-15T18:00:15-07:00</span>
<span class="go">2012-11-01 22:08:41 +0000 +0000</span>
<span class="go">6:00PM</span>
<span class="go">Tue Apr 15 18:00:15 2014</span>
<span class="go">2014-04-15T18:00:15.161182-07:00</span>
<span class="go">0000-01-01 20:41:00 +0000 UTC</span>
<span class="go">2014-04-15T18:00:15-00:00</span>
<span class="go">parsing time &quot;8:41PM&quot; as &quot;Mon Jan _2 15:04:05 2006&quot;: \</span>
<span class="go"> cannot parse &quot;8:41PM&quot; as &quot;Mon&quot;</span>
</pre></div>
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<p class="next">
Next example: <a href="random-numbers">Random Numbers</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/time-formatting-parsing">source</a> | <a href="https://github.com/mmcgrana/gobyexample#license">license</a>
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