Develop Reference

How to properly convert unix timestamp into datetime?

I have a little problem on a Unix Timestamp conversion in DateTime.
This is the Timestamp: 1521932400
I want convert it in DateTime, so I wrote this code:
public static DateTime UnixTimeStampToDateTime(long unixTimeStamp)
{
DateTime dtDateTime = new DateTime(1970, 1, 1, 0, 0, 0, 0);
dtDateTime = dtDateTime.AddSeconds(unixTimeStamp);
return dtDateTime;
}
essentially I declare a DateTime and then add to that the value of the Timestamp, so in this case I'll get: 24/03/2018 23:00:00 but I should get: 25/03/2018 00:00:00.
What I did wrong?

Ok problem solved. I need to convert the DateTime returned from the conversion in my timezone, so I use:
public static DateTime UnixTimeStampToDateTime(long unixTimeStamp)
{
DateTime dtDateTime = new DateTime(1970, 1, 1, 0, 0, 0, 0);
dtDateTime = dtDateTime.AddSeconds(unixTimeStamp);
//Convert in my timezone
TimeZoneInfo timeInfo = TimeZoneInfo.FindSystemTimeZoneById("Central Europe Standard Time");
DateTime userTime = TimeZoneInfo.ConvertTimeFromUtc(dtDateTime, timeInfo);
return userTime;
}

C# Validate the date before inserting them in to mysql

I am working on getting the date validated before we insert them in to the mySQl server. Below is what I am trying
DateTime startDate = new DateTime(2009, 12, 31);
var currentTime = DateTime.Now;
DateTime endDate = currentTime.Date;
DateTime DOB = DateTime.ParseExact(emp[i].DateOfBirth, "yyyy-MM-dd HH:mm:ss,fff", System.Globalization.CultureInfo.InvariantCulture);
if (!(DOB.Date > startDate && DOB.Date <= endDate))
{
WriteValidationFailure("Failed - DOB is Invalid");
}
Here emp[i].DateOfBirth is a string and hold the value like 01/01/2009. When I run the application it throws

You need to use one of these statements to parse your date:
DateTime DOB = DateTime.ParseExact(emp[i].DateOfBirth, "MM/dd/yyyy", System.Globalization.CultureInfo.InvariantCulture);
or
DateTime DOB = DateTime.ParseExact(emp[i].DateOfBirth, "dd/MM/yyyy", System.Globalization.CultureInfo.InvariantCulture);
First if your dates contains month as first part and second for days as first part.

How do I change the date only in a C# DateTime object

I am looking for a elegant solution (if it exists) to achieve what I described in the title.
I saw an elegant solution for "changing the time in a DateTime object" and it is as follows:
DateTime s = ...;
TimeSpan ts = new TimeSpan(10, 30, 0);
s = s.Date + ts;
If there such a solution for changing the date in a DateTime object?

DateTime struct is designed to be immutable, so you can't change it. You can get a new one based on values from the old one, which is exactly what your solution does.
You can make it a bit more clear by using DateTime constructor which takes all date and time values: year, month, day, hour, minute and seconds.
s = new DateTime(s.Year, s.Month, s.Day, 10, 30, 0);
s = new DateTime(2014, 10, 2, s.Hour, s.Minute, s.Second);
or you can use TimeOfDay property:
s = new DateTime(2014, 10, 2) + s.TimeOfDay;

Assuming that you are going to pass a new DateTime object to update your existing object, a function like this can work.
DateTime UpdateDate(DateTime existingDate, DateTime newDate)
{
return newDate.Date + existingDate.TimeOfDay;
}

myDatetime = new DateTime(year, month, day);

You can use the DateTime constructors, so you can preserve the original time.
See this example:
var firstDate = new DateTime(2015, 01, 01, 15, 0, 0);
var newDate = DateTime.Now;
// New date, original time.
firstDate = new DateTime(newDate.Year, newDate.Month, newDate.Day, firstDate.Hour, firstDate.Minute, firstDate.Second, firstDate.Millisecond);

Try this:
DateTime s = ...;
s = new DateTime(year, month, day) + s.TimeOfDay;
That preserves the time in the original DateTime.

Try this:
DateTime now = DateTime.Now;
DateTime dateOnly = now.Date;
TimeSpan time = now.TimeOfDay;
dateOnly = DateTime.Parse("5/15/15"); // or whatever date you choose
DateTime newDateTime = dateOnly + time;

c# Account Expiration Date with dateTimePiker

I would like to set principal.AccountExpirationDate with a dateTimePicker1
if i do this - its work:
principal.AccountExpirationDate = new DateTime(2015, 12, 12);
but when i try to use the dateTimePicker1 its not work - this is my code:
string enddate = dateTimePicker1.Value.ToString("yyyy, MM, dd");
int val = Convert.ToInt32(enddate);
principal.AccountExpirationDate = new DateTime(val);
Im getting error.
how can i covert the dateTimePicker1 to a value that i can set in the principal.AccountExpirationDate?

You cannot convert DateTime or DateTime formated string to integer but you can take dateTime.Day, dateTime.Month or dateTime.Year as an integer separately.
int val = dateTimePicker1.Value.Day;
int month = dateTimePicker1.Value.Month;
int year = dateTimePicker1.Value.Year;
principal.AccountExpirationDate = new DateTime(year, month, val);
But principal.AccountExpirationDate = dateTimePicker1.Value is better one because dateTimePicker1.Value returns DateTime

How to get the Date time month start and End Date?

How to get the start date and end date of month in different variable. I have tried this and I get the start date but unable to find the end date
DateTime startDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1).ToString("yyyy-MM-dd HH:mm:ss.fff");
DateTime endDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1).AddDays(30).ToString("yyyy-MM-dd HH:mm:ss.fff");
This logic fails when month end date is 31 and 28 or 29. Your Help are surely appretiated.

You can calculate endDate like this:
DateTime endDate = startDate.AddMonths(1).AddDays(-1);

To get First Date
public DateTime FirstDayOfMonth(DateTime dateTime)
{
return new DateTime(dateTime.Year, dateTime.Month, 1);
}
To get Last Date
public DateTime LastDayOfMonth(DateTime dateTime)
{
DateTime firstDayOfTheMonth = new DateTime(dateTime.Year, dateTime.Month, 1);
return firstDayOfTheMonth.AddMonths(1).AddDays(-1);
}

DateTime endDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1)
.AddMonths(1).AddDays(-1);

You already had the start date :
DateTime monthStartDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, 1);
There's a method to get the number of days in a month (and Looking at the IL code, it seems that this way is more efficient than the other answers, though unless you're going to do it a billion time, I doubt there will be any difference) :
int daysInMonth = DateTime.DaysInMonth(DateTime.Now.Year, DateTime.Now.Month);
DateTime monthEndDate = new DateTime(DateTime.Now.Year, DateTime.Now.Month, daysInMonth);

For first date:
DateTime first_date = new DateTime(DateTimePicker.Value.Year, DateTimePicker.Value.Month, 1);
For last date:
DateTime last_date = new DateTime(DateTimePicker.Value.Year, DateTimePicker.Value.Month, DateTime.DaysInMonth(DateTimePicker.Value.Year, DateTimePicker.Value.Month));