CODEWITHSUNDEEP
c#
Anthony
Anthony

Reputation: 7300

What is the difference between DateTime.UtcNow and DateTime.Now.ToUniversalTime()

To me they're both the same. Is UtcNow simply a shortcut?

Upvotes: 37

Views: 23522

Answers (5)

areller
areller

Reputation: 5238

It isn't a shortcut, DateTime.Now uses DateTime.UtcNow internally and then applies localization. In short, use ToUniversalTime() if you already have DateTime.Now and need to convert it to UTC, use DateTime.UtcNow if you just want to retrieve the current time in UTC.

Upvotes: 7

Thomas Ayoub
Thomas Ayoub

Reputation: 29431

Well, the actual implementation is (you can see it on referencesource):

public static DateTime Now {
    get {
        Contract.Ensures(Contract.Result<DateTime>().Kind == DateTimeKind.Local);

        DateTime utc = UtcNow; 
        Boolean isAmbiguousLocalDst = false;
        Int64 offset = TimeZoneInfo.GetDateTimeNowUtcOffsetFromUtc(utc, out isAmbiguousLocalDst).Ticks;
        long tick = utc.Ticks + offset;
        if (tick>DateTime.MaxTicks) {
            return new DateTime(DateTime.MaxTicks, DateTimeKind.Local);
        }
        if (tick<DateTime.MinTicks) {
            return new DateTime(DateTime.MinTicks, DateTimeKind.Local);
        }
        return new DateTime(tick, DateTimeKind.Local, isAmbiguousLocalDst);  
    }
}

ToUniversalTime() calls TimeZoneInfo.ConvertTimeToUtc(this, TimeZoneInfoOptions.NoThrowOnInvalidTime)

while UtcNow is just:

long ticks = 0;
ticks = GetSystemTimeAsFileTime();
return new DateTime( ((UInt64)(ticks + FileTimeOffset)) | KindUtc);

Upvotes: 2

Dienekes
Dienekes

Reputation: 1548

I think that using DateTime.UTCNow would consider the DateTime.Kind property's value as UTC whereas with ToUniversalTime you can provide the Kind property with a local datetime object.

Upvotes: 1

Guffa
Guffa

Reputation: 700292

Actually it's the other way around. The Now property is implemented as:

public static DateTime Now {
  get {
    return UtcNow.ToLocalTime();
  }
}

Upvotes: 35

Jamiec
Jamiec

Reputation: 136104

There is a long example in the Documentation for UtcNow which shows them to be the same.

Upvotes: 5

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