# C++ named requirements: UnformattedOutputFunction

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< cpp‎ | named req

### Requirements

A UnformattedOutputFunction is a stream output function that performs the following:

1) Constructs an object of type `basic_ostream::sentry` with automatic storage duration, which performs the following:

- If `eofbit` or `badbit` are set on the output stream, sets the `failbit` as well, and if exceptions on `failbit` are enabled in this output stream's exception mask ((exceptions() & failbit) != 0), throws `ios_base::failure`.
- Flushes the tie()'d output stream, if applicable.

2) Checks the status of the sentry by calling `sentry::operator bool()`, which is equivalent to `basic_ios::good`.

- If the operator returns false or sentry's constructor throws an exception, no output takes place.
- If the operator returns true, attempts to perform the desired output by inserting the characters into the output stream as if by calling rdbuf()->sputc(). Other public members of std::basic_ostream may also be used, but virtual members of rdbuf() except `overflow()`, `xsputn()` and `sync()` will never be called.

  - If an exception is thrown during output, sets `badbit` in the output stream. If exceptions on `badbit` are enabled in this stream's exception mask ((exceptions() & badbit) != 0), the exception is also rethrown.
  - If no exception was thrown, returns the value specified by the function.

3) 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 UnformattedOutputFunctions.

- `basic_ostream::operator<<(basic_streambuf*)`
- `basic_ostream::put`
- `basic_ostream::write`
- `basic_ostream::flush`

- `basic_ostream::tellp` (except calls pubseekoff instead of output)
- `basic_ostream::seekp` (except calls pubseekoff or pubseekpos instead of output)

(since C++11)

### Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR | Applied to | Behavior as published | Correct behavior
--- | --- | --- | ---
LWG 63 | C++98 | the exception-handling policy was missing | added
LWG 160 | C++98 | the process of determining whether the exception caught is rethrown mentioned a non-existing function `exception()` | corrected to `exceptions()`
LWG 165 | C++98 | the only virtual member allowed to be called on rdbuf() was `overflow()` | also allowed `xsputn()` and `sync()`

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