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83 lines
2.8 KiB
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83 lines
2.8 KiB
ReStructuredText
This chapter describes the date and time functions in NSPR.
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NSPR represents time in two ways, absolute time and clock/calendar time.
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NSPR provides types and constants for both representations, and
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functions to convert time values between the two.
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- Absolute time representation treats time instants as points along the
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time line. A time instant is represented by its position on the time
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line relative to the origin, called the epoch. NSPR defines the epoch
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to be midnight (00:00:00) 1 January 1970 UTC (Coordinated Universal
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Time). In this form, time is just a point on the time line. There is
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no notion of time zone.
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- Clock/calendar time, used for human interfaces, represents time in
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the familiar year, month, day, hour, minute, second components. In
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this form, the time zone information is important. For example,
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without specifying the time zone, the time 8:00AM 1 May 1998 is
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ambiguous. The NSPR data type for clock/calendar time, called an
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exploded time, has the time zone information in it, so that its
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corresponding point in absolute time is uniquely specified.
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Note that absolute and clock times are not normally used in timing
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operations. For functions that deal with the measurement of elapsed time
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and with timeouts, see `Interval Timing <Interval_Timing>`__.
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- `Macros for Time Unit
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Conversion <#Macros_for_Time_Unit_Conversion>`__
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- `Types and Constants <#Types_and_Constants>`__
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- `Time Parameter Callback
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Functions <#Time_Parameter_Callback_Functions>`__
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- `Functions <#Functions>`__
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.. _Macros_for_Time_Unit_Conversion:
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Macros for Time Unit Conversion
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-------------------------------
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Macros for converting between seconds, milliseconds, microseconds, and
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nanoseconds.
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- :ref:`PR_MSEC_PER_SEC`
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- :ref:`PR_USEC_PER_SEC`
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- :ref:`PR_NSEC_PER_SEC`
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- :ref:`PR_USEC_PER_MSEC`
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- :ref:`PR_NSEC_PER_MSEC`
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.. _Types_and_Constants:
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Types and Constants
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-------------------
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Types and constants defined for NSPR dates and times are:
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- :ref:`PRTime`
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- :ref:`PRTimeParameters`
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- :ref:`PRExplodedTime`
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.. _Time_Parameter_Callback_Functions:
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Time Parameter Callback Functions
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---------------------------------
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In some geographic locations, use of Daylight Saving Time (DST) and the
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rule for determining the dates on which DST starts and ends have changed
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a few times. Therefore, a callback function is used to determine time
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zone information.
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You can define your own time parameter callback functions, which must
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conform to the definition :ref:`PRTimeParamFn`. Two often-used callback
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functions of this type are provided by NSPR:
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- :ref:`PRTimeParamFn`
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- :ref:`PR_LocalTimeParameters` and :ref:`PR_GMTParameters`
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Functions
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---------
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The functions that create and manipulate time and date values are:
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- :ref:`PR_Now`
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- :ref:`PR_ExplodeTime`
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- :ref:`PR_ImplodeTime`
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- :ref:`PR_NormalizeTime`
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