VB.Net Date.ParseExact Culture issue - vb.net

Question

I am using vb.net and I create a list of months (3 char representation) by using the following function.
Public Function getMonths() As Array
Dim months As String = ""
For i = 1 To 12
months += StrConv(MonthName(i, True), VbStrConv.ProperCase) + ","
Next
months = months.Substring(0, months.Length - 1)
getMonths = months.Split(",")
End Function
This works beautifully, as the site I am building can change language etc on the fly.
However when I try to then change the month back to the numeric value to process using this function
Public Function monthToNumber(ByVal monthin As String, ByVal culture As System.Globalization.CultureInfo) As Integer
monthToNumber = DateTime.ParseExact("01/" + monthin + "/1999", "dd/MMM/yyyy", culture).Month
End Function
, the date.ParseExact throws an exception of date input is not in a valid string.
The month is being produce by the culturalisation, so I can't understand the failure. This only happens with a culture of {pt-PT}. The process works fine for spain, uk, france,italy.

Answer 1

If you use DateTime.ParseExact, you have to use the right DateSeparator.
For pt-PT, it's not /, but -.
/ can work as default DateSeparator, but only if you use CultureInfo.InvariantCulture. But if you do, you can't parse the culture specific date abbreviation.
That's why your code fails.
To generate the month abbreviations, simple use DateTimeFormatInfo.AbbreviatedMonthNames or DateTimeFormatInfo.AbbreviatedMonthGenitiveNames; no need to write a method yourself.
Also, you should look into String.Join (another thing you don't have to reinvent).
For parsing the string back, you could use something like
monthToNumber = DateTime.ParseExact(monthin, "MMM", culture).Month
No need for day/year if you simply use MMM for your format string.