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### 957. Various threading bugs #7

Section: 29.7.2 [time.clock.system] Status: C++11 Submitter: Pete Becker Opened: 2009-01-07 Last modified: 2016-01-28

Priority: Not Prioritized

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Discussion:

29.7.2 [time.clock.system]: `to_time_t` is overspecified. It requires truncation, but should allow rounding. For example, suppose a system has a clock that gives times in milliseconds, but `time()` rounds those times to the nearest second. Then `system_clock` can't use any resolution finer than one second, because if it did, truncating times between half a second and a full second would produce the wrong `time_t` value.

[ Post Summit Anthony Williams provided proposed wording. ]

[ Batavia (2009-05): ]

> Move to Review pending input from Howard. and other stakeholders.

[ 2009-05-23 Howard adds: ]

> I am in favor of the wording provided by Anthony.

[ 2009-10 Santa Cruz: ]

> Move to Ready.

Proposed resolution:

In 29.7.2 [time.clock.system] replace paragraphs 3 and 4 with:

>     time_t to_time_t(const time_point& t);

> > -3- Returns: A `time_t` object that represents the same point in time as `t` when both values are truncated restricted to the coarser of the precisions of `time_t` and `time_point`. It is implementation defined whether values are rounded or truncated to the required precision.

>     time_point from_time_t(time_t t);

> > -4- Returns: A `time_point` object that represents the same point in time as `t` when both values are truncated restricted to the coarser of the precisions of `time_t` and `time_point`. It is implementation defined whether values are rounded or truncated to the required precision.