[R] Creating Rcpp RcppDatetime from string with millisecond

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Hi,

I was trying to generate RcppDatetime from a string. The main problem
for me is that my string contains millisecond. I saw that RcppDatetime
takes in double of seconds since epoch. I try to generate a double
using boost but has no success. I'm wondering if you have any sample
snippet?

The string looks like:

"2010-03-18 15:50:51.232"

Secondly, what time zone RcppDatetime is based on? Is it local machine
time zone? And if I have a need to convert time zone, is there any
tool at hand I can use? Or I have to resort to something like boost
again? Thank you so much in advance.

Rob