29 Input/output library [input.output]

29.7 Formatting and manipulators [iostream.format]

29.7.4 Input streams [input.streams]

29.7.4.2 Formatted input functions [istream.formatted]

29.7.4.2.1 Common requirements [istream.formatted.reqmts]

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Each formatted input function begins execution by constructing an object of class sentry with the noskipws (second) argument false.
If the sentry object returns true, when converted to a value of type bool, the function endeavors to obtain the requested input.
If an exception is thrown during input then ios_­base​::​badbit is turned on303 in *this's error state.
If (exceptions()&badbit) != 0 then the exception is rethrown.
In any case, the formatted input function destroys the sentry object.
If no exception has been thrown, it returns *this.
303)
This is done without causing an ios_­base​::​failure to be thrown.
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29.7.4.2.2 Arithmetic extractors [istream.formatted.arithmetic]

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operator>>(unsigned short& val); operator>>(unsigned int& val); operator>>(long& val); operator>>(unsigned long& val); operator>>(long long& val); operator>>(unsigned long long& val); operator>>(float& val); operator>>(double& val); operator>>(long double& val); operator>>(bool& val); operator>>(void*& val);
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As in the case of the inserters, these extractors depend on the locale's num_­get<> object to perform parsing the input stream data.
These extractors behave as formatted input functions (as described in [istream.formatted.reqmts]).
After a sentry object is constructed, the conversion occurs as if performed by the following code fragment: 
using numget = num_get<charT, istreambuf_iterator<charT, traits>>;
iostate err = iostate::goodbit;
use_facet<numget>(loc).get(*this, 0, *this, err, val);
setstate(err);
In the above fragment, loc stands for the private member of the basic_­ios class.
[ Note
:
The first argument provides an object of the istreambuf_­iterator class which is an iterator pointed to an input stream.
It bypasses istreams and uses streambufs directly.
— end note
 ]
Class locale relies on this type as its interface to istream, so that it does not need to depend directly on istream.
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operator>>(short& val);
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The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment): 
using numget = num_get<charT, istreambuf_iterator<charT, traits>>;
iostate err = ios_base::goodbit;
long lval;
use_facet<numget>(loc).get(*this, 0, *this, err, lval);
if (lval < numeric_limits<short>::min()) {
  err |= ios_base::failbit;
  val = numeric_limits<short>::min();
} else if (numeric_limits<short>::max() < lval) {
  err |= ios_base::failbit;
  val = numeric_limits<short>::max();
}  else
  val = static_cast<short>(lval);
setstate(err);
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operator>>(int& val);
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The conversion occurs as if performed by the following code fragment (using the same notation as for the preceding code fragment): 
using numget = num_get<charT, istreambuf_iterator<charT, traits>>;
iostate err = ios_base::goodbit;
long lval;
use_facet<numget>(loc).get(*this, 0, *this, err, lval);
if (lval < numeric_limits<int>::min()) {
  err |= ios_base::failbit;
  val = numeric_limits<int>::min();
} else if (numeric_limits<int>::max() < lval) {
  err |= ios_base::failbit;
  val = numeric_limits<int>::max();
}  else
  val = static_cast<int>(lval);
setstate(err);

29.7.4.2.3 basic_­istream​::​operator>> [istream.extractors]

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basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& (*pf)(basic_istream<charT, traits>&));
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Effects: None.
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
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Returns: pf(*this).304
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basic_istream<charT, traits>& operator>>(basic_ios<charT, traits>& (*pf)(basic_ios<charT, traits>&));
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Effects: Calls pf(*this).
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
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Returns: *this.
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basic_istream<charT, traits>& operator>>(ios_base& (*pf)(ios_base&));
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Effects: Calls pf(*this).305
This extractor does not behave as a formatted input function (as described in [istream.formatted.reqmts]).
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Returns: *this.
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template<class charT, class traits, size_t N> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& in, charT (&s)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, unsigned char (&s)[N]); template<class traits, size_t N> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, signed char (&s)[N]);
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Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in.
After a sentry object is constructed, operator>> extracts characters and stores them into s.
If width() is greater than zero, n is min(size_­t(width()), N).
Otherwise n is N.
n is the maximum number of characters stored.
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Characters are extracted and stored until any of the following occurs:
  • (8.1)
    n-1 characters are stored;
  • (8.2)
    end of file occurs on the input sequence;
  • (8.3)
    letting ct be use_­facet<ctype<charT>>(in.getloc()), ct.is(ct.space, c) is true.
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operator>> then stores a null byte (charT()) in the next position, which may be the first position if no characters were extracted.
operator>> then calls width(0).
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If the function extracted no characters, it calls setstate(failbit), which may throw ios_­base​::​​failure ([iostate.flags]).
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Returns: in.
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template<class charT, class traits> basic_istream<charT, traits>& operator>>(basic_istream<charT, traits>& in, charT& c); template<class traits> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, unsigned char& c); template<class traits> basic_istream<char, traits>& operator>>(basic_istream<char, traits>& in, signed char& c);
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Effects: Behaves like a formatted input member (as described in [istream.formatted.reqmts]) of in.
After a sentry object is constructed a character is extracted from in, if one is available, and stored in c.
Otherwise, the function calls in.setstate(failbit).
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Returns: in.
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basic_istream<charT, traits>& operator>>(basic_streambuf<charT, traits>* sb);
14
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Effects: Behaves as an unformatted input function.
If sb is null, calls setstate(failbit), which may throw ios_­base​::​failure ([iostate.flags]).
After a sentry object is constructed, extracts characters from *this and inserts them in the output sequence controlled by sb.
Characters are extracted and inserted until any of the following occurs:
  • (14.1)
    end-of-file occurs on the input sequence;
  • (14.2)
    inserting in the output sequence fails (in which case the character to be inserted is not extracted);
  • (14.3)
    an exception occurs (in which case the exception is caught).
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If the function inserts no characters, it calls setstate(failbit), which may throw ios_­base​::​​failure ([iostate.flags]).
If it inserted no characters because it caught an exception thrown while extracting characters from *this and failbit is set in exceptions() ([iostate.flags]), then the caught exception is rethrown.
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Returns: *this.
304)
See, for example, the function signature ws(basic_­istream&) ([istream.manip]).
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305)
See, for example, the function signature dec(ios_­base&).
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