.NET DateTime to time_t in seconds

问题

There is C code :

time1=((double)dt1-25569.0)*86400.0;

it's convert from TDateTime (VCL) to time_t format in seconds, so finally I need to get time_t format from .NET DateTime

about time_t :

It is almost universally expected to be an integral value representing the number of seconds elapsed since 00:00 hours, Jan 1, 1970 UTC. This is due to historical reasons, since it corresponds to a unix timestamp, but is widely implemented in C libraries across all platforms.

So to get seconds in .NET I'm doing this (F#):

let seconds(dt : DateTime) =
    (dt.Ticks/10000000L)

or on C# (to use more popular C# tag) :

Int64 seonds(DateTime dt)
{ return (dt.Ticks/ ((Int64)10000000)); } 
// hope it works, but please correct if I mistaken

As far as I understand it's time from 12:00:00 Jan 1, 0001 UTC.

So to use time_t format I need to add 1970 years in seconds.

So final function must be (F#):

let seconds(dt : DateTime) =
    (dt.Ticks/10000000L) + 31536000*1970

C# :

Int64 seonds(DateTime dt)
{ return (dt.Ticks/ ((Int64)10000000)) + 31536000*1970; }

I really afraid I made mistake here. Please examine this solution ! (check if this is done right)

Thank you

回答1:

try

 (dt - new DateTime (1970, 1, 1)).TotalSeconds

see

http://msdn.microsoft.com/en-us/library/system.timespan.totalseconds.aspx
http://msdn.microsoft.com/en-us/library/xcfzdy4x.aspx

回答2:

this seems a little tidier? You could make the epoch a static datetime if you will be using it a lot.

DateTime date = DateTime.Now;
DateTime epoch = new DateTime(1970, 1, 1);
TimeSpan span = (date - epoch);
double unixTime = span.TotalSeconds;

回答3:

I suggest the following code. It seems to better transport the meaning of the code

private static readonly DateTime REFERENCE = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);

Int64 seconds(DateTime dt)
{
  return (dt - REFERENCE).TotalSeconds;
}

回答4:

In C#:

Int64 Secs(DateTime dt)
{
    var delta = dt - new DateTime(1970, 1, 1);
    return Convert.ToInt64(delta.TotalSeconds);
}

回答5:

After reading @jheriko's comment on the accepted answer I wrote a quick console app to test whether time() from msvcrt.dll produced differing results to calculations using the managed date/time functions, which fortunately they do not, provided UTC is used. Generally speaking, wherever possible, dates and times should be calculated with and stored in UTC as a common base, and then converted back to the relevant timezone for display if necessary.

For reference, and to illustrate different ways of arriving at the number of seconds between 1st Jan 1970 and now, my test code was:

class Program
{
    [DllImport("msvcrt.dll", CallingConvention = CallingConvention.Cdecl)]
    public unsafe static extern int time(int* timer);

    static unsafe void Main(string[] args)
    {
        DateTime now = DateTime.Now;
        DateTime utc_now = DateTime.UtcNow;

        int time_t_msvcrt = time(null);
        int time_t_managed = (int)Math.Floor((now.ToUniversalTime() - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalSeconds);
        int time_t_managed_2 = (int)Math.Floor((utc_now - new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc)).TotalSeconds);

        Console.WriteLine(time_t_msvcrt == time_t_managed);
        Console.WriteLine(time_t_msvcrt == time_t_managed_2);

        DateTime epoch = new DateTime(1970, 1, 1, 0, 0, 0, DateTimeKind.Utc);
        DateTime time_t_now = epoch.Add(TimeSpan.FromSeconds(time_t_msvcrt));

        long now_secs = now.Ticks / 10000000L;
        long utc_now_secs = utc_now.Ticks / 10000000L;
        long time_t_now_secs = time_t_now.Ticks / 10000000L;

        Console.WriteLine(time_t_now_secs == now_secs);
        Console.WriteLine(time_t_now_secs == utc_now_secs);
        Console.ReadLine();
    }
}

This produces the output

True
True
True
True

as expected.

来源：https://stackoverflow.com/questions/7227278/net-datetime-to-time-t-in-seconds

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.net

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datetime