为什么DateTime.ToString没有按预期给出时区

Question

If I have this code:

                DateTime dt = DateTime.UtcNow;
                string sDate = dt.ToString("yyyy-MM-dd HH:mm:ss.fff zz");

my sDate looks like this:

"2013-04-07 21:05:15.396 +10"

which is the current UTC datetime (9:05pm), but with a "+10" on the end which is my local timezone.

I would have expected this:

"2013-04-07 21:05:15.396 +00"

what's going on?

Answer 1

That's because the documentation says (emphasis mine):

With DateTime values, the "zz" custom format specifier represents the signed offset of the local operating system's time zone from UTC, measured in hours. It does not reflect the value of an instance's DateTimeKind property. For this reason, the "zz" format specifier is not recommended for use with DateTime values.

So, the zz format specifier always outputs the UTC offset of your local timezone, even when used to format UTC times.

Answer 2

DateTime.ToString , when you don't pass a CultureInfo into it, defaults to the current culture. If your current culture is +10, then that explains why you see +10. There's various FxCop and Code Analysis rules you can turn on to warn you when you call ToString without a CultureInfo