From cppreference.com
Requirements
A UnformattedOutputFunction is a stream output function that performs the following:
1) Constructs an object of type
with automatic storage duration, which performs the following:
If
or
are set on the output stream, sets the
as well, and if exceptions on failbit are enabled in this output stream's
((exceptions()&failbit)!=0), throws
.
Flushes the tie()'d output stream, if applicable.
2) Checks the status of the sentry by calling sentry::operator bool(), which is equivalent to
.
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
may also be used, but virtual members of rdbuf() except
,
and
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
((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
.
basic_ostream::operator<<(basic_streambuf*)
(except calls pubseekoff instead of output)
(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
C++98 the exception-handling policy was missing added
C++98 the process of determining whether the exception caught
is rethrown mentioned a non-existing function exception()corrected to
C++98 the only virtual member allowed to be
called on rdbuf() was overflow()also allowed
xsputn() and sync()