Returns the internal date number from a string that contains a date in ISO format (YYYYMMDD or YYYY-MM-DD).
The year part must consist of either two (supported only in YYMMDD format without separators for compatibility) or at least four digits. With four digits leading zeros must be given if the absolute value is less than 1000, it can be negative with a leading minus sign if the date passed denotes a year before the common era (BCE) and it can have more than four digits if the absolute value is greater than 9999. The formatted string can be in the range "-327680101" to "327671231", or "-32768-01-01" to "32767-12-31".
An invalid date results in an error. Year 0 is not accepted, the last day BCE is -0001-12-31 and the next day CE is 0001-01-01. Dates before 1582-10-15 are in the proleptic Gregorian calendar.
When converting a date serial number to a printable string, for example for the Print or MsgBox command, the locale's default calendar is used and at that 1582-10-15 cutover date may switch to the Julian calendar, which can result in a different date being displayed than expected. Use the CDateToIso Function to convert such date number to a string representation in the proleptic Gregorian calendar.
The YYYY-MM-DD format with separators is supported since LibreOffice 5.3.4. Years less than 100 or greater than 9999 are accepted since LibreOffice 5.4 if not in VBA compatibility mode.
Internal date number
String: A string that contains a date in ISO format.
dateval = CDateFromIso("20021231")
dateval = CDateFromIso("2002-12-31")
return both 12/31/2002 in the date format of your system