How to get the start and end times of a day

c# datetime

In my C# app, I pass a string variable that is of format yyyymmdd-yyyymmdd that represents a from and to date. I want to get the start and end times for these dates respectively. Currently I have the below code but was wondering if there was more of an elegant solution?

So for pdr = 20090521-20090523 would get "20090521 00:00:00" and "20090523 23:59:59"

private void ValidateDatePeriod(string pdr, out DateTime startDate, 
                                out DateTime endDate)
{
    string[] dates = pdr.Split('-');

    if (dates.Length != 2)
    {
        throw new Exception("Date period is of incorrect format");
    }

    if (dates[0].Length != 8 || dates[1].Length != 8)
    {
        throw new Exception("Split date periods are of incorrect format");
    }

    startDate = DateTime.ParseExact(dates[0] + " 00:00:00", 
        "yyyyMMdd HH:mm:ss", null);
    endDate = DateTime.ParseExact(dates[1] + "23:59:59", 
        "yyyyMMdd HH::mm:ss", null);
}

I am surprised to see how an incorrect answer received so many upvotes:

Wrong value

The correct version would be as follows:

public static DateTime StartOfDay(this DateTime theDate)
{
    return theDate.Date;
}

public static DateTime EndOfDay(this DateTime theDate)
{
    return theDate.Date.AddDays(1).AddTicks(-1);
}

You could define two extension methods somewhere, in a utility class like so :

public static DateTime EndOfDay(this DateTime date)
{
    return new DateTime(date.Year, date.Month, date.Day, 23, 59, 59, 999);
}

public static DateTime StartOfDay(this DateTime date)
{
    return new DateTime(date.Year, date.Month, date.Day, 0, 0, 0, 0);
}

And then use them in code like so :

public DoSomething()
{
    DateTime endOfThisDay = DateTime.Now.EndOfDay();
}

If you are only worried about .Net precision...

startDate = DateTime.ParseExact(dates[0], "yyyyMMdd");
endDate = DateTime.ParseExact(dates[1], "yyyyMMdd").AddTicks(-1).AddDays(1);

You really don't need to concatenate extra values onto the string for the time portion.

As an addendum, if you are using this for a query against, for example, a database...

startDate = DateTime.ParseExact(dates[0], "yyyyMMdd");
endDate = DateTime.ParseExact(dates[1], "yyyyMMdd").AddDays(1);

With a query of...

WHERE "startDate" >= @startDate AND "endDate" < @endDate

Then the precision issues noted in the comments won't really matter. The endDate in this case would not be part of the range, but the outside boundary.

How to get the start and end times of a day

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