哋它亢++ named requirements: UnformattedOutputFunction

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.

The following standard library functions are UnformattedOutputFunctions.

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

(since 哋它亢++11)

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

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

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