HOWTO: Obtain Time Zone Information in Visual FoxPro

ID: Q194576

The information in this article applies to:
  • Microsoft Visual FoxPro for Windows, versions 3.0, 3.0b, 5.0, 5.0a, 6.0

SUMMARY

Use the GetTimeZoneInformation API call to obtain information about the time zone, including the date and time when Daylight Savings Time and Standard Time take effect, the "bias," or time difference between the current time zone and the Coordinated Universal Time, and the current Daylight Savings Time status.


MORE INFORMATION

When the following program is executed, it displays two message boxes. The first displays the current Daylight Savings Time status, either TIME_ZONE_ID_STANDARD if Standard Time is in effect, or TIME_ZONE_ID_DAYLIGHT if Daylight Savings Time is in effect.

When you click OK, the second message box is displayed and includes the following seven items:

  1. The bias, in minutes, from Coordinated Universal Time (UTC). For the "Eastern Time (US & Canada)" time zone, this will be 300. All translations between UTC and local time are based on the following formula: 
    
      UTC = local time + bias


  2. The string description of Standard Time in the current time zone. For example, in the eastern time zone, this string is "Eastern Standard Time."


  3. The month, day, and time when Standard Time goes into effect. The year portion of the date appears to be blank in all cases. The time portion is expressed as a military time.


  4. The bias, in minutes, to be used during local time translations that occur during Standard Time. For most time zones, this value is 0.


  5. The string description of Daylight Savings Time in the current time zone. For example, in the eastern time zone, this string is "Eastern Daylight Time."


  6. The month, day and time when Daylight Savings Time goes into effect. As above, the year portion of the date appears to be blank in all cases.


  7. The Daylight Savings Time bias, in minutes, used during local time translations that occur during daylight time. For most time zones, this value is -60.


Save and execute the following program: 

   #DEFINE ID_INVALID -1
   #DEFINE ID_UNKNOWN 0
   #DEFINE ID_STANDARD 1
   #DEFINE ID_DAYLIGHT 2
   #DEFINE CR CHR(13)

   * the definition for TIME_ZONE_INFORMATION is:
   *
   *typedef struct _TIME_ZONE_INFORMATION { // tzi
   *    LONG       Bias;
   *    WCHAR      StandardName[ 32 ];
   *    SYSTEMTIME StandardDate;
   *    LONG       StandardBias;
   *    WCHAR      DaylightName[ 32 ];
   *    SYSTEMTIME DaylightDate;
   *    LONG       DaylightBias;
   *} TIME_ZONE_INFORMATION;

   * buffer to receive TIME_ZONE_INFORMATION
   TZInfo = SPACE(172)

   DECLARE INTEGER GetTimeZoneInformation IN kernel32 STRING @TZInfo
   liRetCode = GetTimeZoneInformation(@TZInfo)
   DO CASE
      CASE liRetCode = ID_UNKNOWN
         =MESSAGEBOX ("TIME_ZONE_ID_UNKNOWN")
      CASE liRetCode = ID_STANDARD
         =MESSAGEBOX ("TIME_ZONE_ID_STANDARD")
      CASE liRetCode = ID_DAYLIGHT
         =MESSAGEBOX ("TIME_ZONE_ID_DAYLIGHT")
   ENDCASE

   * now, parse the returned structure
   liBias = StrToLong(SUBSTR(TZInfo, 1, 4))

   * lcStandardName is a Unicode string - strip out chr(0)s for
   * US/English
   lcStandardName = SUBSTR(TZInfo, 5, 64)
   lcStandardName = STRTRAN(lcStandardName, CHR(0), "")

   * lcStandardDate is a SYSTEMTIME structure, defined as follows:
   *
   *typedef struct _SYSTEMTIME {  // st
   *    WORD wYear;
   *    WORD wMonth;
   *    WORD wDayOfWeek;
   *    WORD wDay;
   *    WORD wHour;
   *    WORD wMinute;
   *    WORD wSecond;
   *    WORD wMilliseconds;
   *} SYSTEMTIME;

   * this SYSTEMTIME struct must be parsed again
   lcStandardDate = SUBSTR(TZInfo, 69, 16)
   lcSDYear = Str2Word(SUBSTR(lcStandardDate, 1, 2))
   lcSDMonth = Str2Word(SUBSTR(lcStandardDate, 3, 2))
   lcSDDayofWeek = Str2Word(SUBSTR(lcStandardDate, 5, 2))
   lcSDDay = Str2Word(SUBSTR(lcStandardDate, 7, 2))
   lcSDHour = Str2Word(SUBSTR(lcStandardDate, 9, 2))
   lcSDMinute = Str2Word(SUBSTR(lcStandardDate, 11, 2))
   lcSDSecond = Str2Word(SUBSTR(lcStandardDate, 13, 2))
   lcSDMSec = Str2Word(SUBSTR(lcStandardDate, 15, 2))

* format the standard time date for display
   lcStandardDate = PADL(LTRIM(STR(lcSDMonth, 2, 0)), 2,  "0") + "/" + ;
      PADL(LTRIM(STR(lcSDDay, 2, 0)), 2,  "0") + "/" + ;
      PADL(LTRIM(STR(lcSDYear, 2, 0)), 2, "0") + ;
      "   " + ;
      PADL(LTRIM(STR(lcSDHour, 2, 0)), 2, "0") + ":" + ;
      PADL(LTRIM(STR(lcSDMinute, 2, 0)), 2, "0") + ":" + ;
      PADL(LTRIM(STR(lcSDSecond, 2, 0)), 2, "0") + "." + ;
      PADL(LTRIM(STR(lcSDMSec, 3, 0)), 3, "0")

   liStandardBias = StrToLong(SUBSTR(TZInfo, 85, 4))

   * lcDaylightname is also a Unicode string
   lcDaylightName = SUBSTR(TZInfo, 89, 64)
   lcDaylightName = STRTRAN(lcDaylightName, CHR(0), "")

   * this SYSTEMTIME struct must be parsed again, same as above
   lcDaylightDate = SUBSTR(TZInfo, 153, 16)
   lcDDYear = Str2Word(SUBSTR(lcDaylightDate, 1, 2))
   lcDDMonth = Str2Word(SUBSTR(lcDaylightDate, 3, 2))
   lcDDDayofWeek = Str2Word(SUBSTR(lcDaylightDate, 5, 2))
   lcDDDay = Str2Word(SUBSTR(lcDaylightDate, 7, 2))
   lcDDHour = Str2Word(SUBSTR(lcDaylightDate, 9, 2))
   lcDDMinute = Str2Word(SUBSTR(lcDaylightDate, 11, 2))
   lcDDSecond = Str2Word(SUBSTR(lcDaylightDate, 13, 2))
   lcDDMSec = Str2Word(SUBSTR(lcDaylightDate, 15, 2))

   * format the daylight date for display
   lcDaylightDate = PADL(LTRIM(STR(lcDDMonth, 2, 0)), 2, "0") + "/" + ;
      PADL(LTRIM(STR(lcDDDay, 2, 0)), 2, "0") + "/" + ;
      PADL(LTRIM(STR(lcDDYear, 2, 0)), 2, "0") + ;
      "  " + ;
      PADL(LTRIM(STR(lcDDHour, 2, 0)), 2, "0") + ":" + ;
      PADL(LTRIM(STR(lcDDMinute, 2, 0)), 2, "0") + ":" + ;
      PADL(LTRIM(STR(lcDDSecond, 2, 0)), 2, "0") + "." + ;
      PADL(LTRIM(STR(lcDDMSec, 3, 0)), 3, "0")

   * Daylight savings time bias is a negative value
   * stored in 2s complement, so subtract 2^32 to obtain a decimal value
   liDaylightBias = StrToLong(SUBSTR(TZInfo, 169, 4)) - 2 ^ 32

   =MESSAGEBOX("Bias: " + LTRIM(STR(liBias)) + CR + ;
      "Standard name: " + lcStandardName + CR + ;
      "Standard date: " + lcStandardDate + CR + ;
      "Standard bias: " + LTRIM(STR(liStandardBias)) + CR + ;
      "Daylight name: " + lcDaylightName + CR + ;
      "Daylight date: " + lcDaylightDate + CR + ;
      "Daylight bias: " + LTRIM(STR(liDaylightBias)))

   RETURN

   ******************
   FUNCTION StrToLong
   ******************
   * Passed:  4-byte character string (lcLongstr) in low-high ASCII format
   * Returns:  long integer value
   * Example:
   * m.longstr = "1111"
   * m.longval = strtolong(m.longstr)

   PARAMETERS lcLongstr

   PRIVATE i, lnRetval

   lnRetval = 0
   FOR i = 0 TO 24 STEP 8
      lnRetval = lnRetval + (ASC(lcLongstr) * (2^i))
      lcLongstr = RIGHT(lcLongstr, LEN(lcLongstr) - 1)
   NEXT
   RETURN lnRetval

   **********************
   FUNCTION Str2Word

   PARAMETERS m.wordstr

   PRIVATE i, m.retval

   m.retval = 0
   FOR i = 0 TO 8 STEP 8
      m.retval = m.retval + (ASC(m.wordstr) * (2^i))
      m.wordstr = RIGHT(m.wordstr, LEN(m.wordstr) - 1)
   NEXT
   RETURN m.retval


REFERENCES

Win32 API Helpfile

Additional query words: kbVFP600 kbvfp300b kbvfp500a

Keywords :
Version : WINDOWS:3.0,3.0b,5.0,5.0a,6.0
Platform : WINDOWS
Issue type : kbhowto


Last Reviewed: August 9, 1999
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