Bug 967950 - std::chrono clocks changed default resolution
std::chrono clocks changed default resolution
Product: Fedora
Classification: Fedora
Component: gcc (Show other bugs)
Unspecified Unspecified
unspecified Severity unspecified
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Assigned To: Jakub Jelinek
Fedora Extras Quality Assurance
Depends On:
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Reported: 2013-05-28 12:09 EDT by Marcel Hellwig
Modified: 2015-02-18 06:20 EST (History)
5 users (show)

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Doc Type: Bug Fix
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Last Closed: 2015-02-18 06:20:49 EST
Type: Bug
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Description Marcel Hellwig 2013-05-28 12:09:17 EDT
Description of problem:
When compiling simple programm from [0] the times are much higher than with gcc 4.8.0-6. 
Either there is a bug with compilation (I see that in the changelog something with ABI break is mentioned) or the steady clock is not working as expected.

How reproducible:
Compile and run

Actual results:
Much higher times than expected.

[0] http://en.cppreference.com/w/cpp/chrono/steady_clock/now
Comment 1 Jakub Jelinek 2013-05-28 12:25:24 EDT
Why do you think it is a bug?  .count() is really just raw units, the old steady_clock wasn't really steady and had microseconds resolution, the new one (mangles differently; and system_clock too) both have nanosecond resolution.
I guess you want to use other interfaces than .count() if you want to transform it into seconds, microseconds, nanoseconds etc.
Comment 2 Marcel Hellwig 2013-05-28 12:29:42 EDT
Hmmm. Alright. I was wondered because 4.8.0-6 had such "small" numbers and out of the sudden they were that big. And the cppreference had also the small numbers. Thats why I thought it is a bug.
Thanks for your answer.
Comment 3 Benjamin Kosnik 2013-05-29 14:00:17 EDT
Hey Marcel! Yes, the default resolution of the system clocks changed (for the better, IMHO.) That's why you are seeing bigger numbers.

As Jakub stated, this is a feature, not a bug. For typed time values, use c++11's std::duration type. That way you as a programmer can explicitly state the resolution you require, along with the actual value, so that conversions to other resolutions are sane.

Perhaps I should note the change in default clock resolution in 4_8/porting_to.html.

Comment 4 Benjamin Kosnik 2013-05-29 14:01:56 EDT
I'm going to edit this subject so that it's more descriptive.
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