C++ named requirements: UnformattedOutputFunction

Requirements

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

• Constructs an object of type basic_istream::sentry with automatic storage duration and with the noskipws argument set to true, 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.

• 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() & failbit) != 0), the exception is also rethrown.
    • If no exception was thrown, returns the value specified by the function.

• 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) (since C++11)
• 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()