将DateTime.Now转换为秒

Question

I am trying to write a function that will convert a DateTime.Now instance to the number of seconds it represents so that I can compare that to another DateTime instance. Here is what I currently have:

public static int convertDateTimeToSeconds(DateTime dateTimeToConvert)
    {
        int secsInAMin = 60;
        int secsInAnHour = 60 * secsInAMin;
        int secsInADay = 24 * secsInAnHour;
        double secsInAYear = (int)365.25 * secsInADay;

        int totalSeconds = (int)(dateTimeToConvert.Year * secsInAYear) + 
                       (dateTimeToConvert.DayOfYear * secsInADay) +
                       (dateTimeToConvert.Hour * secsInAnHour) +
                       (dateTimeToConvert.Minute * secsInAMin) + 
                       dateTimeToConvert.Second;

        return totalSeconds;
    }

I realize that I am truncating the calculation for seconds in a year, but I don't need my calculation to be precise. I'm really looking to know if the method that I am using to calculate seconds is correct.

Does anyone have anything that could better compute seconds given from a DateTime object?

Also, Should the return type be int64 if I am coding in C# if I am going to calculate all the seconds since 0 AD?

Answer 1

The DateTime type supports comparison operators :

if (dateTimeA > dateTimeB)
{
    ...

This also works for DateTime values returned by DateTime.AddSeconds :

if (dateTimeA.AddSeconds(42) > dateTimeB)
{
    ...

---

If you really want the number of seconds that elapsed since 01/01/0001 00:00:00 , you can calculate the difference between the two DateTime values. The resulting TimeSpan value has a TotalSeconds property:

double result = DateTime.Now.Subtract(DateTime.MinValue).TotalSeconds;

Answer 2

It really doesn't make sense to convert a DateTime object to seconds. Seconds only make sense if you are dealing with a length of time (TimeSpan). Should you want to compare two dates to get the number of seconds between them:

TimeSpan diff = DateTime.Now - PreviousDateTime;
double seconds = diff.TotalSeconds;

Answer 3

See suggestion from thread below:

How do I convert ticks to minutes?

TimeSpan.FromTicks(DateTime.Now.Ticks).TotalSeconds; 

Answer 4

If the purpose is finding the number of seconds between two dates, you'd be much better off using the TimeSpan object.

TimeSpan span = date2 - date1;
double seconds = span.TotalSeconds;

Answer 5

If you want to compare 2 DateTime object, why just not use the provided operators? http://msdn.microsoft.com/en-us/library/aa326723%28v=VS.71%29.aspx

DateTime a, b;
if (a > b) //a is after b

Answer 6

Assuming you really need to get at the seconds for the datetime object, you could directly get the "Ticks" property from it. These aren't in seconds but you can easily divide by the proper factor to convert the Ticks to seconds. See: http://msdn.microsoft.com/en-us/library/system.datetime.ticks.aspx

So, something like:

        DateTime.Now.Ticks/TimeSpan.TicksPerSecond

Answer 7

I would use the TimeSpan class to get the exact difference between two DateTime instances. Here is an example:

  DateTime dt1 = DateTime.Now;
  DateTime dt2 = new DateTime(2003,4,15);
  TimeSpan ts = dt1.Subtract(dt2);

Once the TimeSpan value ( ts , in the code snippet above) is available, you can examine its values to correctly convert the TimeSpan to a given number of seconds.

Answer 8

Using a TimeSpan to get the elapsed time between two DateTimes is probably the best way to go but if you really want to get the number of seconds for a given DateTime you could do something like the following:

DateTime dateTimeToConvert = DateTime.Now;
TimeSpan tsElapsed = dateTimeToConvert - DateTime.MinValue;
return tsElapsed.TotalSeconds;

Note that tsElapsed.TotalSeconds is a Double, not an Int.

Answer 9

Do note that the goal is to get the number of seconds since DateTime.MinVal (the first day of the calendar). I say this, because I see all of these answers for "you do time comparisons like this... add in the object, multiply by that object and do cross-calculus on them, divide by the quotient of the summed result, and Boom! not what you asked."

There's a really simple answer here. Ticks are 100-nanosecond increments. DateTime object.Ticks is the number of ticks that have occurred since 1/1/0001. Ie, year zero. There are 10 million nanoseconds in a second. so...

    public static long convertDateTimeToSeconds(DateTime dateTimeToConvert) {
        // According to Wikipedia, there are 10,000,000 ticks in a second, and Now.Ticks is the span since 1/1/0001. 
        long NumSeconds= dateTimeToConvert.Ticks / 10000000;
        return NumSeconds;
    }