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Inside Macintosh: Operating System Utilities /

Chapter 4 - Date, Time, and Measurement Utilities / Date, Time, and Measurement Utilities Reference

Data Structures

The Geographic Location Record

The geographic ___location and time-zone information of a Macintosh computer are stored in extended parameter RAM. The MachineLocation data type defines the format for the geographic ___location record.

TYPE MachineLocation =  {geographic ___location record}
RECORD
   latitude:            Fract;         {latitude}
   longitude:           Fract;         {longitude}
   CASE Integer OF
   0:
      (dlsDelta:        SignedByte);   {daylight saving time}
   1:
      (gmtDelta:        LongInt);      {Greenwich mean time}
END;

Field Description

latitude

The ___location's latitude, in fractions of a great circle. For example, Copenhagen, Denmark is at 55.43 degrees north latitude. When writing the latitude to extended parameter RAM with the WriteLocation procedure, you must convert this value to a Fract data type. (For example, a Fract value of 1.0 equals 90 degrees; -1.0 equals -90 degrees; and -2.0 equals -180 degrees.) For an example that shows this conversion process, see Listing 4-8 on page 4-19. For more information on the Fract data type, see the chapter "Mathematical and Logical Utilities" in this book.

longitude

The ___location's longitude, in fractions of a great circle. For example, Copenhagen, Denmark is at 12.34 degrees east longitude. When writing the longitude to extended parameter RAM with the WriteLocation procedure, you must convert this value to a Fract data type. (For example, a Fract value of 1.0 equals 90 degrees; -1.0 equals -90 degrees; and -2.0 equals -180 degrees.) For an example that shows this conversion process, see Listing 4-8 on page 4-19. For more information on the Fract data type, see the chapter "Mathematical and Logical Utilities" in this book.

dlsDelta

A signed byte value representing the hour offset for daylight saving time. This field is a 1-byte value contained in a long word. It should be preserved when writing gmtDelta. See Listing 4-10 on page 4-21 for an example that writes gmtDelta while preserving dlsDelta.

gmtDelta

The Greenwich mean time (GMT). For example, Copenhagen, Denmark is at 1 hour west of GMT. This field is a 3-byte value contained in a long word. In addition, the top byte of this field should be masked off when writing because it is reserved. See Listing 4-9 on page 4-20 and Listing 4-10 on page 4-21 for code examples that get and set gmtDelta properly.

The ReadLocation and WriteLocation procedures use the geographic ___location record to read and store the geographic ___location and time zone information in extended parameter RAM. If the geographic ___location record has never been set, all fields contain 0.