95 lines
4.1 KiB
Markdown
95 lines
4.1 KiB
Markdown
[time.clock.file]
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# 30 Time library [[time]](./#time)
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## 30.7 Clocks [[time.clock]](time.clock#file)
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### 30.7.6 Type file_clock [time.clock.file]
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#### [30.7.6.1](#overview) Overview [[time.clock.file.overview]](time.clock.file.overview)
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namespace std::chrono {using file_clock = *see below*;}
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[1](#overview-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L3369)
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file_clock is an alias for a type
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meeting the [*Cpp17TrivialClock*](time.clock.req#:Cpp17TrivialClock "30.3 Cpp17Clock requirements [time.clock.req]") requirements ([[time.clock.req]](time.clock.req "30.3 Cpp17Clock requirements")), and
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using a signed arithmetic type for file_clock::rep[.](#overview-1.sentence-1)
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file_clock is used to create the time_point system
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used for file_time_type ([[filesystems]](filesystems "31.12 File systems"))[.](#overview-1.sentence-2)
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Its epoch is unspecified, andnoexcept(file_clock::now()) is true[.](#overview-1.sentence-3)
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[*Note [1](#overview-note-1)*:
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The type that file_clock denotes can be
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in a different namespace than std::chrono,
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such as std::filesystem[.](#overview-1.sentence-4)
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â *end note*]
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#### [30.7.6.2](#members) Member functions [[time.clock.file.members]](time.clock.file.members)
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[1](#members-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L3386)
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The type denoted by file_clock provides
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precisely one of the following two sets of static member functions:template<class Duration>static sys_time<*see below*> to_sys(const file_time<Duration>&);template<class Duration>static file_time<*see below*> from_sys(const sys_time<Duration>&); or:template<class Duration>static utc_time<*see below*> to_utc(const file_time<Duration>&);template<class Duration>static file_time<*see below*> from_utc(const utc_time<Duration>&);
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These member functions shall provide time_point conversions
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consistent with those specified byutc_clock, tai_clock, and gps_clock[.](#members-1.sentence-2)
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The Duration of the resultant time_point is computed from the Duration of the input time_point[.](#members-1.sentence-3)
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#### [30.7.6.3](#nonmembers) Non-member functions [[time.clock.file.nonmembers]](time.clock.file.nonmembers)
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[ð](#lib:operator%3c%3c,file_time)
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`template<class charT, class traits, class Duration>
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basic_ostream<charT, traits>&
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operator<<(basic_ostream<charT, traits>& os, const file_time<Duration>& t);
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`
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[1](#nonmembers-1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L3423)
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*Effects*: Equivalent to:return os << format(os.getloc(), *STATICALLY-WIDEN*<charT>("{:L%F %T}"), t);
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[ð](#lib:from_stream,file_time)
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`template<class charT, class traits, class Duration, class Alloc = allocator<charT>>
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basic_istream<charT, traits>&
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from_stream(basic_istream<charT, traits>& is, const charT* fmt,
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file_time<Duration>& tp, basic_string<charT, traits, Alloc>* abbrev = nullptr,
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minutes* offset = nullptr);
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`
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[2](#nonmembers-2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L3441)
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*Effects*: Attempts to parse the input stream is into the file_time tp using
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the format flags given in the NTCTS fmt as specified in [[time.parse]](time.parse "30.13 Parsing")[.](#nonmembers-2.sentence-1)
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If the parse fails to decode a valid date,is.setstate(ios_base::failbit) is called andtp is not modified[.](#nonmembers-2.sentence-2)
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If %Z is used and successfully parsed,
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that value will be assigned to *abbrev if abbrev is non-null[.](#nonmembers-2.sentence-3)
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If %z (or a modified variant) is used and successfully parsed,
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that value will be assigned to *offset if offset is non-null[.](#nonmembers-2.sentence-4)
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Additionally, the parsed offset will be subtracted from
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the successfully parsed timestamp prior to assigning that difference to tp[.](#nonmembers-2.sentence-5)
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[3](#nonmembers-3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/time.tex#L3457)
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*Returns*: is[.](#nonmembers-3.sentence-1)
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