Nanosecond civil_time

[rafaelef...@gmail.com]

Hi,

Clock sources provide nanosecond level precision. There are use cases where you want to keep nanoseconds component with civil_time. The simplest one that comes to mind is logging. However, cctz doesn't offer the ability to store the nanosecond component of time as part of the object. As a result, I would be forced to write a wrapper around civil_time to achieve this. For comparison, chrono does offer milli, micro, and nanosecond durations. Boost Date Time also offers nanosecond representation in ptime. I am wondering why isn't there a nanosecond civil_time? Can it be added?

Thank you,

-Rafael

[Greg Miller]

On Wed, Jul 12, 2017 at 11:19 PM, <rafaelef...@gmail.com> wrote:

Hi,

Clock sources provide nanosecond level precision. There are use cases where you want to keep nanoseconds component with civil_time. The simplest one that comes to mind is logging. However, cctz doesn't offer the ability to store the nanosecond component of time as part of the object. As a result, I would be forced to write a wrapper around civil_time to achieve this. For comparison, chrono does offer milli, micro, and nanosecond durations. Boost Date Time also offers nanosecond representation in ptime. I am wondering why isn't there a nanosecond civil_time? Can it be added?

Could it be added? Yes. The reason we haven't added it is that we haven't actually seen the need for it yet. In the case of your example, logging, presumably you want to be logging an absolute time, not a civil time. That is, the input to your logging function would be a std::chrono::time_point (or equivalent), and as you indicated that indeed can be logged with subsecond precision, see https://github.com/google/cctz/blob/master/include/time_zone.h#L221.

So my guess is that if you suspect you need subsecond precision, you probably are actually dealing with absolute times, not civil times. See https://github.com/google/cctz/wiki/FAQ#what-is-an-absolute-time for a description of these terms as I'm using them here.

HTH,

Greg

 

Thank you,

-Rafael

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