31 Input/output library [input.output]

31.7 Formatting and manipulators [iostream.format]

31.7.5 Input streams [input.streams]

31.7.5.3 Formatted input functions [istream.formatted]

31.7.5.3.2 Arithmetic extractors [istream.formatted.arithmetic]

basic_istream& operator>>(unsigned short& val); basic_istream& operator>>(unsigned int& val); basic_istream& operator>>(long& val); basic_istream& operator>>(unsigned long& val); basic_istream& operator>>(long long& val); basic_istream& operator>>(unsigned long long& val); basic_istream& operator>>(float& val); basic_istream& operator>>(double& val); basic_istream& operator>>(long double& val); basic_istream& operator>>(bool& val); basic_istream& operator>>(void*& val);

As in the case of the inserters, these extractors depend on the locale'snum_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, where state represents the input function's local error state:using numget = num_get<charT, istreambuf_iterator<charT, traits>>; use_facet(loc).get(*this, 0, *this, state, val);

In the above fragment,loc stands for the private member of thebasic_ios class.

[Note 1:

The first argument provides an object of theistreambuf_iterator class which is an iterator pointed to an input stream.

It bypasses istreams and uses streambufs directly.

â end note]

Classlocale relies on this type as its interface toistream, so that it does not need to depend directly onistream.

basic_istream& operator>>(short& val);

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>>;long lval; use_facet(loc).get(*this, 0, *this, state, lval);if (lval < numeric_limits::min()) { state |= ios_base::failbit; val = numeric_limits::min();} else if (numeric_limits::max() < lval) { state |= ios_base::failbit; val = numeric_limits::max();} else val = static_cast(lval);

basic_istream& operator>>(int& val);

basic_istream& operator>>(extended-floating-point-type& val);

If the floating-point conversion rank of extended-floating-point-type is not less than or equal to that of long double, then an invocation of the operator function is conditionally supported with implementation-defined semantics.

Otherwise, let FP be a standard floating-point type:

(5.1)

if the floating-point conversion rank of extended-floating-point-type is less than or equal to that of float, then FP is float,

(5.2)

otherwise, if the floating-point conversion rank of extended-floating-point-type is less than or equal to that of double, then FP is double,

(5.3)

otherwise, FP is long double.

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>>; FP fval; use_facet(loc).get(*this, 0, *this, state, fval);if (fval < -numeric_limits<extended-floating-point-type>::max()) { state |= ios_base::failbit; val = -numeric_limits<extended-floating-point-type>::max();} else if (numeric_limits<extended-floating-point-type>::max() < fval) { state |= ios_base::failbit; val = numeric_limits<extended-floating-point-type>::max();} else { val = static_cast<extended-floating-point-type>(fval);}

[Note 2:

When the extended floating-point type has a floating-point conversion rank that is not equal to the rank of any standard floating-point type, then double rounding during the conversion can result in inaccurate results.

from_chars can be used in situations where maximum accuracy is important.