How to truncate milliseconds off of a .NET DateTim

问题:

I\'m trying to compare a time stamp from an incoming request to a database stored value. SQL Server of course keeps some precision of milliseconds on the time, and when read into a .NET DateTime, it includes those milliseconds. The incoming request to the system, however, does not offer that precision, so I need to simply drop the milliseconds.

I feel like I\'m missing something obvious, but I haven\'t found an elegant way to do it (C#).

回答1:

The following will work for a DateTime that has fractional milliseconds, and also preserves the Kind property (Local, Utc or Undefined).

DateTime dateTime = ... anything ...
dateTime = new DateTime(
    dateTime.Ticks - (dateTime.Ticks % TimeSpan.TicksPerSecond), 
    dateTime.Kind
    );

or the equivalent and shorter:

dateTime = dateTime.AddTicks( - (dateTime.Ticks % TimeSpan.TicksPerSecond));

This could be generalized into an extension method:

public static DateTime Truncate(this DateTime dateTime, TimeSpan timeSpan)
{
    if (timeSpan == TimeSpan.Zero) return dateTime; // Or could throw an ArgumentException
    if (dateTime == DateTime.MinValue || dateTime == DateTime.MaxValue) return dateTime; // do not modify \"guard\" values
    return dateTime.AddTicks(-(dateTime.Ticks % timeSpan.Ticks));
}

which is used as follows:

dateTime = dateTime.Truncate(TimeSpan.FromMilliseconds(1)); // Truncate to whole ms
dateTime = dateTime.Truncate(TimeSpan.FromSeconds(1)); // Truncate to whole second
dateTime = dateTime.Truncate(TimeSpan.FromMinutes(1)); // Truncate to whole minute
...

回答2:

var date = DateTime.Now;

date = new DateTime(date.Year, date.Month, date.Day, date.Hour, date.Minute, date.Second, date.Kind);

回答3:

Here is an extension method based on a previous answer that will let you truncate to any resolution...

Usage:

DateTime myDateSansMilliseconds = myDate.Truncate(TimeSpan.TicksPerSecond);
DateTime myDateSansSeconds = myDate.Truncate(TimeSpan.TicksPerMinute)

Class:

public static class DateTimeUtils
{
    /// <summary>
    /// <para>Truncates a DateTime to a specified resolution.</para>
    /// <para>A convenient source for resolution is TimeSpan.TicksPerXXXX constants.</para>
    /// </summary>
    /// <param name=\"date\">The DateTime object to truncate</param>
    /// <param name=\"resolution\">e.g. to round to nearest second, TimeSpan.TicksPerSecond</param>
    /// <returns>Truncated DateTime</returns>
    public static DateTime Truncate(this DateTime date, long resolution)
    {
        return new DateTime(date.Ticks - (date.Ticks % resolution), date.Kind);
    }
}

回答4:

DateTime d = DateTime.Now;
d = d.AddMilliseconds(-d.Millisecond);

回答5:

Instead of dropping the milliseconds then comparing, why not compare the difference?

DateTime x; DateTime y;
bool areEqual = (x-y).TotalSeconds == 0;

or

TimeSpan precision = TimeSpan.FromSeconds(1);
bool areEqual = (x-y).Duration() < precision;

回答6:

Less obvious but more than 2 times faster :

// 10000000 runs

DateTime d = DateTime.Now;

// 484,375ms
d = new DateTime((d.Ticks / TimeSpan.TicksPerSecond) * TimeSpan.TicksPerSecond);

// 1296,875ms
d = d.AddMilliseconds(-d.Millisecond);

回答7:

Sometimes you want to truncate to something calendar-based, like year or month. Here\'s an extension method that lets you choose any resolution.

public enum DateTimeResolution
{
    Year, Month, Day, Hour, Minute, Second, Millisecond, Tick
}

public static DateTime Truncate(this DateTime self, DateTimeResolution resolution = DateTimeResolution.Second)
{
    switch (resolution)
    {
        case DateTimeResolution.Year:
            return new DateTime(self.Year, 1, 1, 0, 0, 0, 0, self.Kind);
        case DateTimeResolution.Month:
            return new DateTime(self.Year, self.Month, 1, 0, 0, 0, self.Kind);
        case DateTimeResolution.Day:
            return new DateTime(self.Year, self.Month, self.Day, 0, 0, 0, self.Kind);
        case DateTimeResolution.Hour:
            return self.AddTicks(-(self.Ticks % TimeSpan.TicksPerHour));
        case DateTimeResolution.Minute:
            return self.AddTicks(-(self.Ticks % TimeSpan.TicksPerMinute));
        case DateTimeResolution.Second:
            return self.AddTicks(-(self.Ticks % TimeSpan.TicksPerSecond));
        case DateTimeResolution.Millisecond:
            return self.AddTicks(-(self.Ticks % TimeSpan.TicksPerMillisecond));
        case DateTimeResolution.Tick:
            return self.AddTicks(0);
        default:
            throw new ArgumentException(\"unrecognized resolution\", \"resolution\");
    }
}

回答8:

Simple...

//Remove milliseconds
DateTime date = DateTime.Now;
date = DateTime.ParseExact(date.ToString(\"yyyy-MM-dd HH:mm:ss\"), \"yyyy-MM-dd HH:mm:ss\", null);

And more...

//Remove seconds
DateTime date = DateTime.Now;
date = DateTime.ParseExact(date.ToString(\"yyyy-MM-dd HH:mm\"), \"yyyy-MM-dd HH:mm\", null);

//Remove minutes
DateTime date = DateTime.Now;
date = DateTime.ParseExact(date.ToString(\"yyyy-MM-dd HH\"), \"yyyy-MM-dd HH\", null);

//and go on...

回答9:

Regarding Diadistis response. This worked for me, except I had to use Floor to remove the fractional part of the division before the multiplication. So,

d = new DateTime((d.Ticks / TimeSpan.TicksPerSecond) * TimeSpan.TicksPerSecond);

becomes

d = new DateTime(Math.Floor(d.Ticks / TimeSpan.TicksPerSecond) * TimeSpan.TicksPerSecond);

I would have expected the division of two Long values to result in a Long, thus removing the decimal part, but it resolves it as a Double leaving the exact same value after the multiplication.

Eppsy

回答10:

2 Extension methods for the solutions mentioned above

    public static bool LiesAfterIgnoringMilliseconds(this DateTime theDate, DateTime compareDate, DateTimeKind kind)
    {
        DateTime thisDate = new DateTime(theDate.Year, theDate.Month, theDate.Day, theDate.Hour, theDate.Minute, theDate.Second, kind);
        compareDate = new DateTime(compareDate.Year, compareDate.Month, compareDate.Day, compareDate.Hour, compareDate.Minute, compareDate.Second, kind);

        return thisDate > compareDate;
    }


    public static bool LiesAfterOrEqualsIgnoringMilliseconds(this DateTime theDate, DateTime compareDate, DateTimeKind kind)
    {
        DateTime thisDate = new DateTime(theDate.Year, theDate.Month, theDate.Day, theDate.Hour, theDate.Minute, theDate.Second, kind);
        compareDate = new DateTime(compareDate.Year, compareDate.Month, compareDate.Day, compareDate.Hour, compareDate.Minute, compareDate.Second, kind);

        return thisDate >= compareDate;
    }

usage:

bool liesAfter = myObject.DateProperty.LiesAfterOrEqualsIgnoringMilliseconds(startDateTime, DateTimeKind.Utc);

回答11:

DateID.Text = DateTime.Today.ToShortDateString();

Use ToShortDateString() //Date 2-02-2016
Use ToShortDateString() // Time 

And By Use Of

ToLongDateString() // its show 19 February 2016.

:P

回答12:

New Method

String Date = DateTime.Today.ToString(\"dd-MMM-yyyy\"); 

// define String pass parameter dd-mmm-yyyy return 24-feb-2016

Or shown on textbox

txtDate.Text = DateTime.Today.ToString(\"dd-MMM-yyyy\");

// put on PageonLoad

回答13:

To round down to the second:

dateTime.AddTicks(-dateTime.Ticks % TimeSpan.TicksPerSecond)

Replace with TicksPerMinute to round down to the minute.

---

If your code is performance sensitive, be cautious about

new DateTime(date.Year, date.Month, date.Day, date.Hour, date.Minute, date.Second)

My app was spending 12% of CPU time in System.DateTime.GetDatePart.