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    <p>In case you're curious, the TDateTime is encoded as floating point <code>Double</code> internally. </p> <p><strong>TDateTime internals</strong><br> The fractional part denotes the time, the integer part denotes the date.<br> Knowing this the following tests will evaluate to <code>true</code>.</p> <pre><code>dtTime: ABS(Double(DateTime1)) &lt; 1.0 dtDate: Trunc(Double(DateTime1)) = Double(DateTime1) dtDateTime: ( (ABS(Double(DateTime1)) &gt; 1.0) and (Trunc(Double(DateTime1)) &lt;&gt; Double(DateTime1)) ) </code></pre> <p>Obviously that's a very roundabout way of testing, but sometimes it helps to know how a TDateTime is shaped internally. </p> <p><strong>DateUtils</strong><br> The sane versions of these tests would be: </p> <pre><code>uses DateUtils; dtDate: DateTime1 = DateOf(DateTime1) dtTime: DateTime1 = TimeOf(DateTime1) dtDateTime:(DateTime1 &lt;&gt; DateOf(DateTime1)) and (DateTime1 &lt;&gt; TimeOf(DateTime1)) </code></pre> <p><strong>TDateTime is compatible with Excel</strong><br> The value <code>0</code> links to the epoch in Microsoft's Excel: 30 December 1899; 12:00 A.M.<br> <em><sup>(It should have been 1-1-1900, but they changed it to compensate for an error in Lotus' 123 date algorithm)</sup></em><br> This is great, because Delphi's <code>TDateTime</code> is fully compatible with Excel's DateTime. </p> <p>Here's the official doc: <a href="http://docwiki.embarcadero.com/Libraries/XE5//en/System.TDateTime" rel="nofollow">http://docwiki.embarcadero.com/Libraries/XE5//en/System.TDateTime</a></p>
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    1. POHow know type variable is TDateTime, TDate and TTime in Delphi
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    1. USJohan
    1. USJohan
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    1. CO"There are no negative dates!" Obviously we don't have the same dating experience. ;-)
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      1. USalcalde
    2. COYou don't really get a choice of whether to use -ve dates or not - you either need to represent a pre-1900 date or you don't. I can see how the time segment could be confusing, though.
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      1. USMatt Allwood
    3. CO@MattAllwood Sure you can roll your own, but don't expect RTL support (DateToStr) etc. Oh and pre 1900 dates are complicated. See wikipedia.
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