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    10 <!DOCTYPE concept

    11   PUBLIC "-//OASIS//DTD DITA Concept//EN" "concept.dtd">

    12 <concept id="GUID-B1DD21A3-674A-5193-95CF-F533FDBBD319" xml:lang="en"><title>Using

    13 Date and Time Handling</title><shortdesc>Explains how to manipulate Date and Time.</shortdesc><prolog><metadata><keywords/></metadata></prolog><conbody>

    14 <p>Points in time are stored and manipulated using the <codeph>TTime</codeph> class. <codeph>TTime</codeph> uses

    15 a 64-bit integer to represent time as the number of microseconds since midnight

    16 on 1st January 0 AD, using a nominal Gregorian calendar. This gives a possible

    17 range of 580,000 years.</p>

    18 <p>The date/time and its individual components may be set and retrieved using

    19 the <codeph>TDateTime</codeph> class. <codeph>TDateTime</codeph> is the human

    20 readable form of <codeph>TTime</codeph>. It is provided to allow easy user

    21 access to the year, month, day, hour, minute, second and microsecond components

    22 of the time. It does not support manipulation of the date/time, or of its

    23 components, but may be converted into a <codeph>TTime</codeph>, and vice versa.</p>

    24 <p>Intervals between points in time are represented by the classes derived

    25 from <codeph>TTimeIntervalBase</codeph> and by class <codeph>TTimeIntervalMicroSeconds</codeph>.

    26 Time intervals can be added or subtracted, either to or from each other or

    27 to or from points in time. Time interval classes exist because adding two

    28 points in time or subtracting one point in time from another is not possible.</p>

    29 <p>The <codeph>Time</codeph> class is a collection of time related utility

    30 functions; for example, functions that check for leap years and return the

    31 number of days in the month.</p>

    32 <section id="GUID-EA8DB5D2-2979-44A9-9D12-AB454050B03E"><title>Arithmetic operations</title> <p>Care should be taken when

    33 performing arithmetic operations on <codeph>TTime</codeph> s especially when

    34 dealing with the last day in the month. For example: </p> <ul>

    35 <li id="GUID-81A3ED23-55B5-5BEF-A2C5-D05458512637"><p>adding one month to

    36 October 18th adds 31 days</p> </li>

    37 <li id="GUID-CBF68BC9-7F83-5FEC-B5BC-2E63906A5747"><p>adding one month to

    38 November 18th adds 30 days</p> </li>

    39 <li id="GUID-019F031D-5228-594E-8ECF-9DCAA7C04B09"><p>adding one year to February

    40 29th, 1996 gives Feb 28th, 1997</p> </li>

    41 <li id="GUID-D019C0F8-9B74-5405-82D4-1ECEB7C3329B"><p>adding one month to

    42 March 31st gives April 30th but subtracting one month from April 30th gives

    43 March 30th</p> </li>

    44 </ul> </section>

    45 </conbody></concept>