What is the best way to convert seconds into (Hour:Minutes:Seconds:Milliseconds) time?

Question

For .Net <= 4.0 Use the TimeSpan class.

TimeSpan t = TimeSpan.FromSeconds( secs );

string answer = string.Format("{0:D2}h:{1:D2}m:{2:D2}s:{3:D3}ms", 
                t.Hours, 
                t.Minutes, 
                t.Seconds, 
                t.Milliseconds);

(As noted by Inder Kumar Rathore) For .NET > 4.0 you can use

TimeSpan time = TimeSpan.FromSeconds(seconds);

//here backslash is must to tell that colon is
//not the part of format, it just a character that we want in output
string str = time .ToString(@"hh\:mm\:ss\:fff");

(From Nick Molyneux) Ensure that seconds is less than TimeSpan.MaxValue.TotalSeconds to avoid an exception.

For .NET > 4.0 you can use

TimeSpan time = TimeSpan.FromSeconds(seconds);

//here backslash is must to tell that colon is
//not the part of format, it just a character that we want in output
string str = time .ToString(@"hh\:mm\:ss\:fff");

or if you want date time format then you can also do this

TimeSpan time = TimeSpan.FromSeconds(seconds);
DateTime dateTime = DateTime.Today.Add(time);
string displayTime = dateTime.ToString("hh:mm:tt");

For more you can check Custom TimeSpan Format Strings

If you know you have a number of seconds, you can create a TimeSpan value by calling TimeSpan.FromSeconds:

 TimeSpan ts = TimeSpan.FromSeconds(80);

You can then obtain the number of days, hours, minutes, or seconds. Or use one of the ToString overloads to output it in whatever manner you like.

I did some benchmarks to see what's the fastest way and these are my results and conclusions. I ran each method 10M times and added a comment with the average time per run.

If your input milliseconds are not limited to one day (your result may be 143:59:59.999), these are the options, from faster to slower:

// 0.86 ms
static string Method1(int millisecs)
{
    int hours = millisecs / 3600000;
    int mins = (millisecs % 3600000) / 60000;
    // Make sure you use the appropriate decimal separator
    return string.Format("{0:D2}:{1:D2}:{2:D2}.{3:D3}", hours, mins, millisecs % 60000 / 1000, millisecs % 1000);
}

// 0.89 ms
static string Method2(int millisecs)
{
    double s = millisecs % 60000 / 1000.0;
    millisecs /= 60000;
    int mins = millisecs % 60;
    int hours = millisecs / 60;
    return string.Format("{0:D2}:{1:D2}:{2:00.000}", hours, mins, s);
}

// 0.95 ms
static string Method3(int millisecs)
{
    TimeSpan t = TimeSpan.FromMilliseconds(millisecs);
    // Make sure you use the appropriate decimal separator
    return string.Format("{0:D2}:{1:D2}:{2:D2}.{3:D3}",
        (int)t.TotalHours,
        t.Minutes,
        t.Seconds,
        t.Milliseconds);
}

If your input milliseconds are limited to one day (your result will never be greater then 23:59:59.999), these are the options, from faster to slower:

// 0.58 ms
static string Method5(int millisecs)
{
    // Fastest way to create a DateTime at midnight
    // Make sure you use the appropriate decimal separator
    return DateTime.FromBinary(599266080000000000).AddMilliseconds(millisecs).ToString("HH:mm:ss.fff");
}

// 0.59 ms
static string Method4(int millisecs)
{
    // Make sure you use the appropriate decimal separator
    return TimeSpan.FromMilliseconds(millisecs).ToString(@"hh\:mm\:ss\.fff");
}

// 0.93 ms
static string Method6(int millisecs)
{
    TimeSpan t = TimeSpan.FromMilliseconds(millisecs);
    // Make sure you use the appropriate decimal separator
    return string.Format("{0:D2}:{1:D2}:{2:D2}.{3:D3}",
        t.Hours,
        t.Minutes,
        t.Seconds,
        t.Milliseconds);
}

In case your input is just seconds, the methods are slightly faster. Again, if your input seconds are not limited to one day (your result may be 143:59:59):

// 0.63 ms
static string Method1(int secs)
{
    int hours = secs / 3600;
    int mins = (secs % 3600) / 60;
    secs = secs % 60;
    return string.Format("{0:D2}:{1:D2}:{2:D2}", hours, mins, secs);
}

// 0.64 ms
static string Method2(int secs)
{
    int s = secs % 60;
    secs /= 60;
    int mins = secs % 60;
    int hours = secs / 60;
    return string.Format("{0:D2}:{1:D2}:{2:D2}", hours, mins, s);
}

// 0.70 ms
static string Method3(int secs)
{
    TimeSpan t = TimeSpan.FromSeconds(secs);
    return string.Format("{0:D2}:{1:D2}:{2:D2}",
        (int)t.TotalHours,
        t.Minutes,
        t.Seconds);
}

And if your input seconds are limited to one day (your result will never be greater then 23:59:59):

// 0.33 ms
static string Method5(int secs)
{
    // Fastest way to create a DateTime at midnight
    return DateTime.FromBinary(599266080000000000).AddSeconds(secs).ToString("HH:mm:ss");
}

// 0.34 ms
static string Method4(int secs)
{
    return TimeSpan.FromSeconds(secs).ToString(@"hh\:mm\:ss");
}

// 0.70 ms
static string Method6(int secs)
{
    TimeSpan t = TimeSpan.FromSeconds(secs);
    return string.Format("{0:D2}:{1:D2}:{2:D2}",
        t.Hours,
        t.Minutes,
        t.Seconds);
}

As a final comment, let me add that I noticed that string.Format is a bit faster if you use D2 instead of 00.

TimeSpan.FromSeconds(80);

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

The TimeSpan constructor allows you to pass in seconds. Simply declare a variable of type TimeSpan amount of seconds. Ex:

TimeSpan span = new TimeSpan(0, 0, 500);
span.ToString();

I'd suggest you use the TimeSpan class for this.

public static void Main(string[] args)
{
    TimeSpan t = TimeSpan.FromSeconds(80);
    Console.WriteLine(t.ToString());

    t = TimeSpan.FromSeconds(868693412);
    Console.WriteLine(t.ToString());
}

Outputs:

00:01:20
10054.07:43:32