CODEWITHSUNDEEP
.netdatetime
Razer
Razer

Reputation: 13

AddDays() is not incrementing month

In my code AddDays(1) is working correctly for all days except the last day of the month.

I have a datatable containing data read in from a csv. Each row contains a date as string in format yyyy-mm-dd. I want to add a day this date. The code below is working for all dates where the day is not the last day of the month, but fails to increment the month otherwise.

Example:

2019-07-30 correctly increments to 2019-07-31, but 2019-07-31 increments to 2019-07-01 rather than to 2019-08-01.

I've tried Date.Parse, and tried using System.Globalization.CultureInfo.InvariantCulture or System.Globalization.DateTimeFormatInfo.InvariantInfo without success.

MS documentation says

The AddDays method takes into account leap years and the number of days in a month when performing date arithmetic.

What am I doing wrong?

Dim enUK As New System.Globalization.CultureInfo("en-UK")
For Each row As DataRow In Outs.Select
   Dim Lastdate As Date = DateTime.ParseExact(row("EndDate"), "yyyy-mm-dd", enUK) 
   Dim DepDate As Date = Lastdate.AddDays(1)
   row("Date") = DepDate.ToString("yyyy-mm-dd")
Next

I expect the value of row("Date") to be 2019-08-01 for a row("EndDate") value of 2019-07-31, rather than the value I'm getting of 2019-07-01.

Upvotes: 1

Views: 332

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1503449

You're using mm in your format string, which means minutes rather than months. So you're not parsing the date correctly to start with. You want something like:

Dim enUK As New System.Globalization.CultureInfo("en-UK")
For Each row As DataRow In Outs.Select
   Dim Lastdate As Date = DateTime.ParseExact(row("EndDate"), "yyyy-MM-dd", enUK) 
   Dim DepDate As Date = Lastdate.AddDays(1)
   row("Date") = DepDate.ToString("yyyy-MM-dd", enUK)
Next

Note that I've also added the enUK argument to ToString - otherwise if your current thread culture uses a different calendar system, you could get some very odd results.

Upvotes: 3

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