为什么C＃DateTime字符串格式不起作用？

Question

The following code doesn't format the time properly. All I want is minutes:seconds:milliseconds_with_3_decimals but no matter what formatting I choose it gets ignored and the time is displayed with default formatting.

Log(LogMsgType.Normal, String.Format("+{0:mm:ss.fff} ", DateTime.Now.Subtract(latest)));

Answer 1

You need to look into formatting of TimeSpan , not DateTime . This was new in .NET 4.0 (Visual Studio 2010). See: MSDN: Custom TimeSpan Format Strings .

I would try something like:

String.Format("+{0:mm':'ss'.'fff} ", DateTime.Now - latest)

(Better check first that it's never over 60 minutes, otherwise you will lose the most significant part of the time span.)

NOTE: If you're on .NET 3.5 or earlier, this won't work as TimeSpan wasn't IFormattable in those versions. In that case I recommend:

var span = DateTime.Now - latest;
  ...
String.Format("+{0:D2}:{1:D2}.{2:D3} ", span.Minutes, span.Seconds, span.Milliseconds)

Answer 2

You want:

@"+{0:mm\:ss\.fff} "

You have to escape the colon and period