[istream.formatted.reqmts]

# 31 Input/output library [[input.output]](./#input.output)

## 31.7 Formatting and manipulators [[iostream.format]](iostream.format#istream.formatted.reqmts)

### 31.7.5 Input streams [[input.streams]](input.streams#istream.formatted.reqmts)

#### 31.7.5.3 Formatted input functions [[istream.formatted]](istream.formatted#reqmts)

#### 31.7.5.3.1 Common requirements [istream.formatted.reqmts]

[1](#1)

[#](http://github.com/Eelis/draft/tree/9adde4bc1c62ec234483e63ea3b70a59724c745a/source/iostreams.tex#L4655)

Each formatted input function begins execution by constructing
an object of type ios_base​::​iostate, termed the local error state, and
initializing it to ios_base​::​goodbit[.](#1.sentence-1)

It then creates an object of classsentry with thenoskipws (second) argumentfalse[.](#1.sentence-2)

If thesentry object returnstrue,
when converted to a value of typebool,
the function endeavors
to obtain the requested input[.](#1.sentence-3)

Otherwise,
if the sentry constructor exits by throwing an exception or
if the sentry object produces false when converted to a value of type bool,
the function returns without attempting to obtain any input[.](#1.sentence-4)

If rdbuf()->sbumpc() or rdbuf()->sgetc() returns traits​::​eof(), thenios_base​::​eofbit is set in the local error state and
the input function stops trying to obtain the requested input[.](#1.sentence-5)

If an exception is thrown during input thenios_base​::​badbit is set in the local error state,*this's error state is set to the local error state, and
the exception is rethrown if (exceptions() & badbit) != 0[.](#1.sentence-6)

After extraction is done, the input function calls setstate, which
sets *this's error state to the local error state, and
may throw an exception[.](#1.sentence-7)

In any case, the formatted input function destroys thesentry object[.](#1.sentence-8)

If no exception has been thrown, it returns*this[.](#1.sentence-9)