Re: [Boost-users] [boost][chrono] time_since_epoch different on windows and linux

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On 08/12/2011 at 23:57, in message , Klaim - Joël Lamotte wrote: Hi,

The documentation makes clear that epoch is implementation dependent :

"The library leaves epochs unspecified."

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From : http://www.boost.org/doc/libs/1_48_0/doc/html/chrono.html

"In each of the examples above, a different epoch is implied. Sometimes an epoch has meaning for several millennia. Other times the meaning of an epoch is lost after a while (such as the start of a timer, or when the computer booted). However, if two

time_point<http://www.boost.org/doc/libs/1_48_0/doc/html/chrono/reference.htm

l#chrono.reference.cpp0x.time_point_hpp.time_point>s are known to share the same epoch, they can be subtracted, yielding a valid

duration<http://www.boost.org/doc/libs/1_48_0/doc/html/chrono/reference.html#

chrono.reference.cpp0x.duration_hpp.duration>, even if the definition of the epoch no longer has meaning.

In *Boost.Chrono*, an epoch is a purely abstract and unspecified concept. There is no type representing an epoch. It is simply an idea that relates (or doesn't)

time_point<http://www.boost.org/doc/libs/1_48_0/doc/html/chrono/reference.htm

l#chrono.reference.cpp0x.time_point_hpp.time_point>s to a clock, and in the case that they share a clock,

time_point<http://www.boost.org/doc/libs/1_48_0/doc/html/chrono/reference.htm

l#chrono.reference.cpp0x.time_point_hpp.time_point>s to one another.

time_point<http://www.boost.org/doc/libs/1_48_0/doc/html/chrono/reference.htm

l#chrono.reference.cpp0x.time_point_hpp.time_point>s associated with different clocks are generally not interoperable unless the relationship between the epochs associated with each clock is known."

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From http://www.boost.org/doc/libs/1_48_0/doc/html/chrono/users_guide.html

My understanding is that chrono isn't meant to provide absolute time "position", but time measurement and manipulations. The difference being that epoch is an arbitrary referential used to

allow

now() to be written and worked with.

Joël Lamotte

Thanks a lot for the clarification Joël, I had read the quoted section, but interpreted it incorrectly. Regards, Ralf -- This message is subject to the CSIR's copyright terms and conditions, e-mail legal notice, and implemented Open Document Format (ODF) standard. The full disclaimer details can be found at http://www.csir.co.za/disclaimer.html. This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean.