Performs setup work for output streams.
Objects of this class are created before all of the standard inserters are run. It is responsible for exception-safe prefix and suffix operations.
|std::basic_ostream::sentry::sentry||(||basic_ostream< _CharT, _Traits > &||__os||)||
The constructor performs preparatory work.
|os||The output stream to guard.|
If the stream state is good (os.good() is true), then if the stream is tied to another output stream,
is.tie()->flush() is called to synchronize the output sequences.
If the stream state is still good, then the sentry state becomes true (okay).
|std::basic_ostream::sentry::operator bool||(||)|| const