Why is my DateTime.Now.Millisecond value always "000"?

Question

I want my millisecond value to always be three characters long, so I'm padding it, where necessary, with "0"s:

private String getPlatypusFileName(String billNum)
{
    const string basePortion = "Platypus_";
    String PlatypusFileName;
    DateTime dt = DateTime.Now;
    int Year = dt.Year;
    int Month = dt.Month;
    int Day = dt.Day;
    int Hour = dt.Hour;
    int Minute = dt.Minute;
    int Second = dt.Second;
    int Millisecond = dt.Millisecond;
    String paddedBillNum = Prepad(6, billNum);
    String mon = Prepad(2, Month.ToString());
    String day = Prepad(2, Day.ToString());
    String hour = Prepad(2, Hour.ToString());
    String min = Prepad(2, Minute.ToString());
    String sec = Prepad(2, Second.ToString());
    String milli = Prepad(3, Millisecond.ToString());
    PlatypusFileName = String.Format("{0}{1}_{2}{3}{4}{5}{6}{7}_{8}.xml", 
        basePortion, paddedBillNum, Year, mon, day, hour, min, sec, milli);
    return PlatypusFileName;
}

private String Prepad(int finalSize, String originalVal)
{
    String paddedVal = originalVal;
    while (paddedVal.Length < finalSize)
    {
        paddedVal = "0" + paddedVal;
    }
    return paddedVal;
}

...but I'm always getting vals with three "0"s for the millisecond portion; the returned values are like so:

Platypus_000003_20141008145606_000.xml

Why would that be?

Answer 1

Your code should work fine, as written, except that you're probably running on Windows Compact Framework. As mentioned here, the CF always returns 0 for DateTime.Millisecond, so some other approach will be necessary if you need to have that accuracy, such as looking at Environment.TickCount.

That being said, you don't need to use Prepad here - just format appropriately:

const string basePortion = "Platypus_";
DateTime dt = DateTime.Now;
int billNum = 3;

string result = string.Format("{0}{1:000000}_{2}{3:00}{4:00}{5:00}{6:00}{7:00}_{8:00}.xml",
    basePortion, 
    billNum, 
    dt.Year,
    dt.Month,
    dt.Day,
    dt.Hour,
    dt.Minute,
    dt.Second,
    dt.Millisecond);

On my system, this prints out a value of: Platypus_000003_20141008121707_894.xml - Though that changes each time it's run, of course.

Answer 2

Why don't you use standard datetime.toString("special_format_string"). Learn methods of the string class, also learn about formats. You don't need even Prepad method.

All you need is one simple method:

    private String getPlatypusFileName(String billNum)
    {
        const string basePortion = "Platypus_";
        String PlatypusFileName;
        DateTime dt = DateTime.Now;
        PlatypusFileName = String.Format("{0}{1}_{2}.xml",
            basePortion, billNum.PadLeft(6,'0'), dt.ToString("yyyyMMddHHmmss_fff"));
        return PlatypusFileName;
    }

More over, don't use const if you don't know what it for. Also I'm sure that the base type of billNum source also is int, so you do not need any special method, you already have method string.Format(), just use it wisely. All your code can be replaced with one statement:

int billNum = 23;
string PlatypusFileName = string.Format("Platypus_{0:D6}_{1:yyyyMMddHHmmss_fff}.xml", billNum, DateTime.Now);

Answer 3

Since this is, indeed, a CF project and, as Reed Copsey pointed out, I'm doomed to zilches in that environment for milliseconds (and it seems seconds, too), I (since I don't really need accurate seconds/milliseconds values, just "something") did this:

    . . .
    String pseudoSeconds = GetRandomIntAsStr(10,59);
    String fauxMilliseconds = GetRandomIntAsStr(100, 999);
    return String.Format("{0}-{1}-{2} {3}:{4}:{5}.{6}", year, month, day, hour, minute, pseudoSeconds, fauxMilliseconds);
    . . .

// ad[a,o]pted from http://www.whypad.com/posts/csharp-get-a-random-number-between-x-and-y/412/
internal static String GetRandomIntAsStr(int min, int max)
{
    Random rnd = new Random();
    int val = rnd.Next(min, max);
    return val.ToString();
}

And I get values such as "44.766" for the randomized portions of the string.