title: Reading dates from OpenXml Excel files
body: <p>I'm trying to read data from the .xlsx files using SharpZipLib to unpack it (in memory) and reading the inner xml files. Everything is fine but recognizing the dates - they're stored in julean format and I need to somehow recognize if a number is a date or only a number. In another topic (unfortunately it died and I need quick answer) I got to know some things from Mark Baker, but it's still not enough...</p>
  <blockquote>
  <p>&quot;Excel stores dates as a float value... the integer part being the number of days since 1/1/1900 (or 1/1/1904 depending on which calendar is being used), the fractional part being the proportion of a day (ie the time part)... made slightly more awkward by the fact that 1900 is considered a leap year.</p>
  <p>The only thing that differentiates a data from a number is the number format mask. If you can read the format mask, you can use that to identify the value as a date rather than a number... then calculate the date value/formatting from the base date.&quot;</p>
  <p><em><strong>&quot;But doesn't the attribute &quot;s&quot; for dates has always the value of &quot;1&quot;? I know it defines style, but maybe? ;)&quot;</strong></em></p>
  <p>The s attribute references a style xf entry in styles.xml, and it won't always be entry 1 for dates... it all depends how many different styles are being used in the workbook. The style xf in turn references a number format mask. To identify a cell that contains a date, you need to perform the style xf -&gt; numberformat lookup, then identify whether that numberformat mask is a date/time numberformat mask (rather than, for example, a percentage or an accounting numberformat mask)</p>
  <p><em><strong>&quot;One more question - I'm now looking at the style.xml's content and in the  section I see elements like: &quot;&lt;xf numFmtId=&quot;14&quot; ... applyNumberFormat=&quot;1&quot; /&gt;&quot;, &quot;&lt;xf numFmtId=&quot;1&quot; ... applyNumberFormat=&quot;1&quot; /&gt;&quot;, etc. but there is no &lt;numFmts&gt; section... Are there any &quot;standard&quot; formats? Or am I just missing something?&quot;</strong></em></p>
  </blockquote>
  <p>Can someone please help me out? Thanks in advance.</p>