How can I get UTC ,regardless of the current system Time.

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Hello,
I want to show clock to users regardless system time.it may system time is not set.
when i use this code:

C#

DateTime.UtcNow

and my system time is not correct,this time too is not correct.

how do i utcNow with a time zone that save in database.

i want to get utcNow.TimeOfDay and sum with timeZone and show to user,correct time.

how can do it?

thank you in advance.

Posted 15-Dec-15 1:28am

NewWebDesigner

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Comments

Nathan Minier 15-Dec-15 7:43am

NTP to the rescue!

There are a couple of sample methods that will get you rolling on this SO thread:
http://stackoverflow.com/questions/1193955/how-to-query-an-ntp-server-using-c

Jochen Arndt 15-Dec-15 7:51am

If you need a correct time source you must provide one. This is usually the system time. You may also get it from a time server using NTP. But the system is able to do the same and that is the preferred way.

Some time zone definition will not solve your problem. Handling with time zones is not necessary and will introduce additional imponderabilia.

Sergey Alexandrovich Kryukov 15-Dec-15 11:09am

All correct, would make a fair formal answer.
I would start with this: System.DateTime.UtcNow does work correctly, but the system time might be wrong. Strictly speaking, time zone is irrelevant. A system can be set to any valid time zone, as soon as the time set is consistent with that zone. And it does not matter how the time is set with NTP or just manually; it just has to be correct.
—SA

NewWebDesigner 16-Dec-15 2:21am

ok,but you say time can set manually!when time is not correct,utcNow too not correct.
is there other way to get right time,without using NTP or API?
If Server Time is correct,and client system Time is not,is it UTCNOW correct?

2 solutions

Solution 1

To do this functionality you will need a NTP client. There are several implementations, but over time it will drift, due to the internal task switcher in the OS, so periodically you will have to update the over NTP to get the correct value.

To answer your previous question, the server UTC time will be correct, regardless of your current system time. That's the whole point of NTP. Make your life easier: don't try to reimplement the wheel :)

Posted 16-Dec-15 21:46pm

webmaster442

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NewWebDesigner 17-Dec-15 4:20am

ok,can you give me an example of use NTP client?I dont know about it.

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webmaster442 · Accepted Answer · 2015-12-16T23:45:00

Code from http://stackoverflow.com/questions/1193955/how-to-query-an-ntp-server-using-c[^]

C#

public static DateTime GetNetworkTime()
{
    //default Windows time server
    const string ntpServer = "time.windows.com";

    // NTP message size - 16 bytes of the digest (RFC 2030)
    var ntpData = new byte[48];

    //Setting the Leap Indicator, Version Number and Mode values
    ntpData[0] = 0x1B; //LI = 0 (no warning), VN = 3 (IPv4 only), Mode = 3 (Client Mode)

    var addresses = Dns.GetHostEntry(ntpServer).AddressList;

    //The UDP port number assigned to NTP is 123
    var ipEndPoint = new IPEndPoint(addresses[0], 123);
    //NTP uses UDP
    var socket = new Socket(AddressFamily.InterNetwork, SocketType.Dgram, ProtocolType.Udp);

    socket.Connect(ipEndPoint);

    //Stops code hang if NTP is blocked
    socket.ReceiveTimeout = 3000;     

    socket.Send(ntpData);
    socket.Receive(ntpData);
    socket.Close();

    //Offset to get to the "Transmit Timestamp" field (time at which the reply 
    //departed the server for the client, in 64-bit timestamp format."
    const byte serverReplyTime = 40;

    //Get the seconds part
    ulong intPart = BitConverter.ToUInt32(ntpData, serverReplyTime);

    //Get the seconds fraction
    ulong fractPart = BitConverter.ToUInt32(ntpData, serverReplyTime + 4);

    //Convert From big-endian to little-endian
    intPart = SwapEndianness(intPart);
    fractPart = SwapEndianness(fractPart);

    var milliseconds = (intPart * 1000) + ((fractPart * 1000) / 0x100000000L);

    //**UTC** time
    var networkDateTime = (new DateTime(1900, 1, 1, 0, 0, 0, DateTimeKind.Utc)).AddMilliseconds((long)milliseconds);

    return networkDateTime.ToLocalTime();
}

// stackoverflow.com/a/3294698/162671
static uint SwapEndianness(ulong x)
{
    return (uint) (((x & 0x000000ff) << 24) +
                   ((x & 0x0000ff00) << 8) +
                   ((x & 0x00ff0000) >> 8) +
                   ((x & 0xff000000) >> 24));
}