C++ In a Nutshell

Name

basic_ostream::sentry class — Sentry class for output streams

Synopsis

template <class charT,class traits = char_traits<charT> >
class basic_ostream<charT,traits>::sentry {
public:
  explicit sentry(basic_ostream<charT,traits>& os);
  ~sentry(  );
  operator bool(  ) const;
private:
  sentry(const sentry&);            // Not defined
  sentry& operator=(const sentry&); // Not defined
};

A basic_ostream object constructs a temporary sentry object prior to each output operation. The sentry object is destroyed when the output operation finishes and the function returns. The sentry manages tied streams and unit buffering.

The stream passes itself to the sentry’s constructor. If stream.good( ) is true, the sentry first flushes any tied stream. That is, if stream.tie( ) is not null, the sentry calls stream.tie( )->flush( ).

If sentry preparation fails, badbit is set.

The sentry destructor flushes the buffer if the unitbuf flag is on and the output function did not throw an exception:

if ((os.flags(  ) & ios_base::unitbuf) && !uncaught_exception(  ))
  os.flush(  );

See Also

basic_ostream class template, basic_ios in <ios>