std::ostreambuf_iterator<CharT,Traits>::failed
From cppreference.com
                    
                                        
                    < cpp | iterator | ostreambuf iterator
                    
                                                            
                    bool failed() const throw();  | 
(until C++11) | |
|   bool failed() const noexcept;  | 
(since C++11) | |
Returns true if the iterator encountered the end-of-file condition, that is, if an earlier call to std::basic_streambuf::sputc (made by operator=) returned Traits::eof.
Parameters
(none)
Return value
true if this iterator has encountered the end-of-file condition on output, false otherwise.
Example
| This section is incomplete Reason: no example  |