System::TDateTime is the C++ analog for the Delphi System::TDateTime data type.
TDateTime = class(TDateTimeBase);
class TDateTime : public TDateTimeBase;
System::TDateTime implements the Delphi System::TDateTime data type and the date/time runtime library routines that use the System::TDateTime data type.
The System::TDateTime class inherits a val data member declared as a double that holds the date-time value. The integral part of a System::TDateTime value is the number of days that have passed since 12/30/1899. The fractional part of a System::TDateTime value is the time of day.
Following are some examples of System::TDateTime values and their corresponding dates and times:
0 12/30/1899 12:00 am
2.75 1/1/1900 6:00 pm
-1.25 12/29/1899 6:00 am
35065 1/1/1996 12:00 am
To find the fractional number of days between two dates, simply subtract the two values, unless one of the System::TDateTime values is negative. Similarly, to increment a date and time value by a certain fractional number of days, add the fractional number to the date and time value if the System::TDateTime value is positive.
When working with negative System::TDateTime values, computations must handle time portion separately. The fractional part reflects the fraction of a 24-hour day without regard to the sign of the System::TDateTime value. For example, 6:00 am on 12/29/1899 is –1.25, not –1 + 0.25, which would be –0.75. There are no System::TDateTime values between –1 and 0.
istream& operator >> (istream& is, System::TDateTime& arg);
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