81 lines
3.0 KiB
Markdown
81 lines
3.0 KiB
Markdown
[ostream.sentry]
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# 31 Input/output library [[input.output]](./#input.output)
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## 31.7 Formatting and manipulators [[iostream.format]](iostream.format#ostream.sentry)
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### 31.7.6 Output streams [[output.streams]](output.streams#ostream.sentry)
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#### 31.7.6.2 Class template basic_ostream [[ostream]](ostream#sentry)
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#### 31.7.6.2.4 Class basic_ostream::sentry [ostream.sentry]
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[ð](#lib:basic_ostream::sentry)
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namespace std {template<class charT, class traits>class basic_ostream<charT, traits>::sentry {bool *ok_*; // *exposition only*public:explicit sentry(basic_ostream& os); ~sentry(); explicit operator bool() const { return *ok_*; } sentry(const sentry&) = delete;
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sentry& operator=(const sentry&) = delete; };}
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[1](#1)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L6205)
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The classsentry defines a class that is responsible for doing exception safe prefix and suffix
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operations[.](#1.sentence-1)
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[ð](#lib:basic_ostream::sentry,constructor)
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`explicit sentry(basic_ostream& os);
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`
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[2](#2)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L6217)
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Ifos.good() is nonzero, prepares for formatted or unformatted output[.](#2.sentence-1)
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Ifos.tie() is not a null pointer, callsos.tie()->flush()[.](#2.sentence-2)[283](#footnote-283 "The call os.tie()->flush() does not necessarily occur if the function can determine that no synchronization is necessary.")
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[3](#3)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L6233)
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If, after any preparation is completed,os.good() istrue,*ok_* == true otherwise,*ok_* == false[.](#3.sentence-1)
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During preparation, the constructor may callsetstate(failbit) (which may throwios_base::failure ([[iostate.flags]](iostate.flags "31.5.4.4 Flags functions")))[.](#3.sentence-2)[284](#footnote-284 "The sentry constructor and destructor can also perform additional implementation-dependent operations.")
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[ð](#lib:basic_ostream::sentry,destructor)
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`~sentry();
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`
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[4](#4)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L6261)
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If(os.flags() & ios_base::unitbuf) && !uncaught_exceptions()&& os.good() istrue,
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callsos.rdbuf()->pubsync()[.](#4.sentence-1)
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If that function returns â1 or
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exits via an exception, sets badbit inos.rdstate() without propagating an exception[.](#4.sentence-2)
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[ð](#lib:operator_bool,basic_ostream::sentry)
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`explicit operator bool() const;
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`
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[5](#5)
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[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L6279)
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*Effects*: Returns*ok_*[.](#5.sentence-1)
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[283)](#footnote-283)[283)](#footnoteref-283)
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The callos.tie()->flush() does not necessarily occur if the function can determine that no
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synchronization is necessary[.](#footnote-283.sentence-1)
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[284)](#footnote-284)[284)](#footnoteref-284)
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Thesentry constructor and destructor
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can also perform additionalimplementation-dependent operations[.](#footnote-284.sentence-1)
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