find time from four bytes

Question

program in c# find time :
byte [] a = new byte { 224 , 198 , 23 , 200 }; Console . WriteLine ( "time {0} " , BitConverter . ToInt32 ( a , 0 )); output: -939765856
what wrong in program ,i use Convert.ToDateTime but not has correct output
i want a 32 bit integer that specifies(in seconds since midnight,january 1, 1904)

Vulpes · Accepted Answer

Well, as the result can't be negative, may be the bytes represent an unsigned integer rather than a signed integer?
If we assume that we get:
byte[] a = new byte[] {224,198,23,200};
uint ui = BitConverter.ToUInt32(a,0);
DateTime dt = new DateTime(1904, 1, 1);
dt = dt.AddSeconds(ui);
Console.WriteLine(dt);
This gives 03:24:00 on 18 May 2010.

Vulpes · Answer

Yes, you can use any 'base' date you like.
I only used 1/1/1904 because this was the date you used yourself in your opening post.

zozo ahmed · Answer

thank you so much ,but why use 1904 can i use (1980,1,1)??
i am beginner in c# and i need to understand why use  year (1904)

Vulpes · Answer

We need to work backwards to find the equivalent byte array for that.
Ignoring any adjustment for local time/UTC:
DateTime dt = new DateTime(1904, 1, 1);       DateTime dt2 = new DateTime(2013, 9, 9, 11, 52, 0);       uint ui = (uint)(dt2 - dt).TotalSeconds;       byte[] a = BitConverter.GetBytes(ui);       foreach(byte b in a) Console.Write("{0} ", b);
This gives:
224 102 83 206

zozo ahmed · Answer

ok thanks,can time gives
9/9/2013 11:52:00