tmp/tmpfmytc0mo/{from.md → to.md}
RENAMED
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| 1 |
+
##### Class `basic_istream::sentry` <a id="istream.sentry">[[istream.sentry]]</a>
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``` cpp
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namespace std {
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template<class charT, class traits = char_traits<charT>>
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class basic_istream<charT, traits>::sentry {
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bool ok_; // exposition only
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public:
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explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false);
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~sentry();
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explicit operator bool() const { return ok_; }
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sentry(const sentry&) = delete;
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sentry& operator=(const sentry&) = delete;
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};
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}
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```
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The class `sentry` defines a class that is responsible for doing
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exception safe prefix and suffix operations.
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``` cpp
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explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false);
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```
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*Effects:* If `is.good()` is `false`, calls `is.setstate(failbit)`.
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Otherwise, prepares for formatted or unformatted input. First, if
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`is.tie()` is not a null pointer, the function calls `is.tie()->flush()`
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to synchronize the output sequence with any associated external C
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stream. Except that this call can be suppressed if the put area of
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`is.tie()` is empty. Further an implementation is allowed to defer the
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call to `flush` until a call of `is.rdbuf()->underflow()` occurs. If no
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such call occurs before the `sentry` object is destroyed, the call to
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`flush` may be eliminated entirely.[^18] If `noskipws` is zero and
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`is.flags() & ios_base::skipws` is nonzero, the function extracts and
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discards each character as long as the next available input character
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`c` is a whitespace character. If `is.rdbuf()->sbumpc()` or
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`is.rdbuf()->sgetc()` returns `traits::eof()`, the function calls
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`setstate(failbit | eofbit)` (which may throw `ios_base::failure`).
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*Remarks:* The constructor
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``` cpp
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explicit sentry(basic_istream<charT, traits>& is, bool noskipws = false)
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```
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uses the currently imbued locale in `is`, to determine whether the next
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input character is whitespace or not.
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To decide if the character `c` is a whitespace character, the
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constructor performs as if it executes the following code fragment:
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``` cpp
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const ctype<charT>& ctype = use_facet<ctype<charT>>(is.getloc());
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if (ctype.is(ctype.space, c) != 0)
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// c is a whitespace character.
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```
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If, after any preparation is completed, `is.good()` is `true`,
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`ok_ != false` otherwise, `ok_ == false`. During preparation, the
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constructor may call `setstate(failbit)` (which may throw
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`ios_base::failure` [[iostate.flags]]).[^19]
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``` cpp
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~sentry();
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```
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*Effects:* None.
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``` cpp
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explicit operator bool() const;
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```
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*Returns:* `ok_`.
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