Parsing an ISO8601 date/time (including TimeZone) in Excel

Question

I need to parse an ISO8601 date/time format with an included timezone (from an external source) in Excel/VBA, to a normal Excel Date. As far as I can tell, Excel XP (which is what we're using) doesn't have a routine for that built-in, so I guess I'm looking at a custom VBA function for the parsing.

ISO8601 datetimes look like one of these:

2011-01-01
2011-01-01T12:00:00Z
2011-01-01T12:00:00+05:00
2011-01-01T12:00:00-05:00
2011-01-01T12:00:00.05381+05:00

Answer 1

There is a (reasonably) simple way to parse an ISO timestamp WITHOUT the time zone using formulas instead of macros. This is not exactly what the original poster has asked, but I found this question when trying to parse ISO timestamps in Excel and found this solution useful, so I thought I would share it here.

The following formula will parse an ISO timestamp, again WITHOUT the time zone:

=DATEVALUE(MID(A1,1,10))+TIMEVALUE(MID(A1,12,8))

This will produce the date in floating point format, which you can then format as a date using normal Excel formats.

Answer 2

A lot of Googling didn't turn up anything so I write my own routine. Posting it here for future reference:

Option Explicit

'---------------------------------------------------------------------
' Declarations must be at the top -- see below
'---------------------------------------------------------------------
Public Declare Function SystemTimeToFileTime Lib _
  "kernel32" (lpSystemTime As SYSTEMTIME, _
  lpFileTime As FILETIME) As Long

Public Declare Function FileTimeToLocalFileTime Lib _
  "kernel32" (lpLocalFileTime As FILETIME, _
  lpFileTime As FILETIME) As Long

Public Declare Function FileTimeToSystemTime Lib _
  "kernel32" (lpFileTime As FILETIME, lpSystemTime _
  As SYSTEMTIME) As Long

Public Type FILETIME
    dwLowDateTime As Long
    dwHighDateTime As Long
End Type

Public Type SYSTEMTIME
    wYear As Integer
    wMonth As Integer
    wDayOfWeek As Integer
    wDay As Integer
    wHour As Integer
    wMinute As Integer
    wSecond As Integer
    wMilliseconds As Integer
End Type

'---------------------------------------------------------------------
' Convert ISO8601 dateTimes to Excel Dates
'---------------------------------------------------------------------
Public Function ISODATE(iso As String)
    ' Find location of delimiters in input string
    Dim tPos As Integer: tPos = InStr(iso, "T")
    If tPos = 0 Then tPos = Len(iso) + 1
    Dim zPos As Integer: zPos = InStr(iso, "Z")
    If zPos = 0 Then zPos = InStr(iso, "+")
    If zPos = 0 Then zPos = InStr(tPos, iso, "-")
    If zPos = 0 Then zPos = Len(iso) + 1
    If zPos = tPos Then zPos = tPos + 1

    ' Get the relevant parts out
    Dim datePart As String: datePart = Mid(iso, 1, tPos - 1)
    Dim timePart As String: timePart = Mid(iso, tPos + 1, zPos - tPos - 1)
    Dim dotPos As Integer: dotPos = InStr(timePart, ".")
    If dotPos = 0 Then dotPos = Len(timePart) + 1
    timePart = Left(timePart, dotPos - 1)

    ' Have them parsed separately by Excel
    Dim d As Date: d = DateValue(datePart)
    Dim t As Date: If timePart <> "" Then t = TimeValue(timePart)
    Dim dt As Date: dt = d + t

    ' Add the timezone
    Dim tz As String: tz = Mid(iso, zPos)
    If tz <> "" And Left(tz, 1) <> "Z" Then
        Dim colonPos As Integer: colonPos = InStr(tz, ":")
        If colonPos = 0 Then colonPos = Len(tz) + 1

        Dim minutes As Integer: minutes = CInt(Mid(tz, 2, colonPos - 2)) * 60 + CInt(Mid(tz, colonPos + 1))
        If Left(tz, 1) = "+" Then minutes = -minutes
        dt = DateAdd("n", minutes, dt)
    End If

    ' Return value is the ISO8601 date in the local time zone
    dt = UTCToLocalTime(dt)
    ISODATE = dt
End Function

'---------------------------------------------------------------------
' Got this function to convert local date to UTC date from
' http://excel.tips.net/Pages/T002185_Automatically_Converting_to_GMT.html
'---------------------------------------------------------------------
Public Function UTCToLocalTime(dteTime As Date) As Date
    Dim infile As FILETIME
    Dim outfile As FILETIME
    Dim insys As SYSTEMTIME
    Dim outsys As SYSTEMTIME

    insys.wYear = CInt(Year(dteTime))
    insys.wMonth = CInt(Month(dteTime))
    insys.wDay = CInt(Day(dteTime))
    insys.wHour = CInt(Hour(dteTime))
    insys.wMinute = CInt(Minute(dteTime))
    insys.wSecond = CInt(Second(dteTime))

    Call SystemTimeToFileTime(insys, infile)
    Call FileTimeToLocalFileTime(infile, outfile)
    Call FileTimeToSystemTime(outfile, outsys)

    UTCToLocalTime = CDate(outsys.wMonth & "/" & _
      outsys.wDay & "/" & _
      outsys.wYear & " " & _
      outsys.wHour & ":" & _
      outsys.wMinute & ":" & _
      outsys.wSecond)
End Function

'---------------------------------------------------------------------
' Tests for the ISO Date functions
'---------------------------------------------------------------------
Public Sub ISODateTest()
    ' [[ Verify that all dateTime formats parse sucesfully ]]
    Dim d1 As Date: d1 = ISODATE("2011-01-01")
    Dim d2 As Date: d2 = ISODATE("2011-01-01T00:00:00")
    Dim d3 As Date: d3 = ISODATE("2011-01-01T00:00:00Z")
    Dim d4 As Date: d4 = ISODATE("2011-01-01T12:00:00Z")
    Dim d5 As Date: d5 = ISODATE("2011-01-01T12:00:00+05:00")
    Dim d6 As Date: d6 = ISODATE("2011-01-01T12:00:00-05:00")
    Dim d7 As Date: d7 = ISODATE("2011-01-01T12:00:00.05381+05:00")
    AssertEqual "Date and midnight", d1, d2
    AssertEqual "With and without Z", d2, d3
    AssertEqual "With timezone", -5, DateDiff("h", d4, d5)
    AssertEqual "Timezone Difference", 10, DateDiff("h", d5, d6)
    AssertEqual "Ignore subsecond", d5, d7

    ' [[ Independence of local DST ]]
    ' Verify that a date in winter and a date in summer parse to the same Hour value
    Dim w As Date: w = ISODATE("2010-02-23T21:04:48+01:00")
    Dim s As Date: s = ISODATE("2010-07-23T21:04:48+01:00")
    AssertEqual "Winter/Summer hours", Hour(w), Hour(s)

    MsgBox "All tests passed succesfully!"
End Sub

Sub AssertEqual(name, x, y)
    If x <> y Then Err.Raise 1234, Description:="Failed: " & name & ": '" & x & "' <> '" & y & "'"
End Sub

Answer 3

I know its not as elegant as VB module but if someone is looking for a quick formula which consider time zone after '+' as well then this could be it.

= DATEVALUE(MID(D3,1,10))+TIMEVALUE(MID(D3,12,5))+TIME(MID(D3,18,2),0,0)

will change

2017-12-01T11:03+1100

to

2/12/2017 07:03:00 AM

(local time considering timezone)

obviously, u can modify the length of different trimming sections, if u got milliseconds as well or if you got longer time after +.

use sigpwned formula if you want to ignore timezone.

Answer 4

I would have posted this as a comment, but I don't have enough rep - sorry!. This was really useful for me - thanks rix0rrr, but I noticed that the UTCToLocalTime function needs to take account of regional settings when constructing the date at the end. Here's the version I use in the UK - note that the order of wDay and wMonth are reversed:

Public Function UTCToLocalTime(dteTime As Date) As Date
  Dim infile As FILETIME
  Dim outfile As FILETIME
  Dim insys As SYSTEMTIME
  Dim outsys As SYSTEMTIME

  insys.wYear = CInt(Year(dteTime))
  insys.wMonth = CInt(Month(dteTime))
  insys.wDay = CInt(Day(dteTime))
  insys.wHour = CInt(Hour(dteTime))
  insys.wMinute = CInt(Minute(dteTime))
  insys.wSecond = CInt(Second(dteTime))

  Call SystemTimeToFileTime(insys, infile)
  Call FileTimeToLocalFileTime(infile, outfile)
  Call FileTimeToSystemTime(outfile, outsys)

  UTCToLocalTime = CDate(outsys.wDay & "/" & _
    outsys.wMonth & "/" & _
    outsys.wYear & " " & _
    outsys.wHour & ":" & _
    outsys.wMinute & ":" & _
    outsys.wSecond)
  End Function