Getting current GMT time

问题:

Is there a method in C# that returns the UTC (GMT) time zone? Not based on the system's time.

Basically I want to get the correct UTC time even if my system time is not right.

回答1:

Instead of calling

DateTime.Now.ToUniversalTime()

you can call

DateTime.UtcNow

Same thing but shorter :) Documentation here.

回答2:

Not based on the system's time? You'd need to make a call to a network time service or something similar. You could write an NTP client, or just screenscrape World Clock ;)

I don't believe .NET has an NTP client built in, but there are quite a few available.

回答3:

I use this from UNITY

//Get a NTP time from NIST
//do not request a nist date more than once every 4 seconds, or the connection will be refused.
//more servers at tf.nist.goc/tf-cgi/servers.cgi
public static DateTime GetDummyDate()
{
    return new DateTime(1000, 1, 1); //to check if we have an online date or not.
}
public static DateTime GetNISTDate()
{
    Random ran = new Random(DateTime.Now.Millisecond);
    DateTime date = GetDummyDate();
    string serverResponse = string.Empty;

    // Represents the list of NIST servers
    string[] servers = new string[] {
        "nist1-ny.ustiming.org",
        "time-a.nist.gov",
        "nist1-chi.ustiming.org",
        "time.nist.gov",
        "ntp-nist.ldsbc.edu",
        "nist1-la.ustiming.org"                         
    };

    // Try each server in random order to avoid blocked requests due to too frequent request
    for (int i = 0; i < 5; i++)
    {
        try
        {
            // Open a StreamReader to a random time server
            StreamReader reader = new StreamReader(new System.Net.Sockets.TcpClient(servers[ran.Next(0, servers.Length)], 13).GetStream());
            serverResponse = reader.ReadToEnd();
            reader.Close();

            // Check to see that the signature is there
            if (serverResponse.Length > 47 && serverResponse.Substring(38, 9).Equals("UTC(NIST)"))
            {
                // Parse the date
                int jd = int.Parse(serverResponse.Substring(1, 5));
                int yr = int.Parse(serverResponse.Substring(7, 2));
                int mo = int.Parse(serverResponse.Substring(10, 2));
                int dy = int.Parse(serverResponse.Substring(13, 2));
                int hr = int.Parse(serverResponse.Substring(16, 2));
                int mm = int.Parse(serverResponse.Substring(19, 2));
                int sc = int.Parse(serverResponse.Substring(22, 2));

                if (jd > 51544)
                    yr += 2000;
                else
                    yr += 1999;

                date = new DateTime(yr, mo, dy, hr, mm, sc);

                // Exit the loop
                break;
            }
        }
        catch (Exception ex)
        {
            /* Do Nothing...try the next server */
        }
    }
return date;
}

回答4:

If I were to wager a guess for how to get a guaranteed accurate time, you'd have to find / write some NNTP class to get the time off of a time server.

If you search C# NTP on google you can find a few implementations, otherwise check the NTP protocol.

回答5:

If your system time is not right, nothing that you get out of the DateTime class will help. Your system can sync the time with time servers though, so if that is turned on, the various DateTime UTC methods/properties will return the correct UTC time.