# C++ concepts: FormattedInputFunction

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### Requirements

A `FormattedInputFunction` is a stream input function that performs the following:

- Constructs an object of type `basic_istream::sentry` with automatic storage duration and with the `noskipws` argument set to false, which performs the following

  - if `eofbit` or `badbit` are set on the input stream, sets the `failbit` as well, and if exceptions on failbit are enabled in this input stream's exception mask, throws `ios_base::failure`.
  - flushes the tie()'d output stream, if applicable
  - if `ios_base::skipws` flag is set on this input stream, extracts and discards characters from the input stream until one of the following becomes true:
    - the next available character on the input stream is not a whitespace character, as tested by the std::ctype facet of the locale currently imbued in this input stream. The non-whitespace character is not extracted.
    - the end of the stream is reached, in which case `failbit` and `eofbit` are set and if the stream is on for exceptions on one of these bits, `ios_base::failure` is thrown.

- Checks the status of the sentry by calling `sentry::operator bool()`, which is equivalent to `basic_ios::good`.
- If the sentry returned false or sentry's constructor threw an exception, no input takes place
- If the sentry returned true, performs the input as if by calling rdbuf()->sbumpc() or rdbuf()->sgetc().

  - if the end of the stream is reached (the call to rdbuf()->sbumpc() or rdbuf()->sgetc() returns Traits::eof(), sets `eofbit`. If exceptions on eofbit are enabled in this stream's exception mask, throws `ios_base::failure`.
  - if an exception is thrown during input, sets `badbit` in the input stream. If exceptions on badbit are enabled in this stream's exception mask, the exception is also rethrown.
  - If no exception was thrown, returns *this.

- In any event, whether terminating by exception or returning, the sentry's destructor is called before leaving this function.

### Standard library

The following standard library functions are `FormattedInputFunction`s.

- `basic_istream::operator>>(int, long, double, void*, bool)`
- `operator>>(std::basic_istream, char&)`
- `operator>>(std::basic_istream, char*)`
- `operator>>(std::basic_istream, std::bitset)`
- `operator>>(std::basic_istream, std::string)`
- `operator>>`, when called on the return value of std::get_money

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