The standard library sets badbit in the following situations:

• Insertion into the output stream by put() or write() fails for any
  reason.

• Insertion into the output stream by operator<<,std::put_money or
  std::put_time,could not complete because the end of the output
  stream was reached (The facet’s formatting output function such as
  num_put::put() or money_put::put(),returns an iterator iter such
  that iter.Failed()==true)

• Stream is constructed with a null pointer for rdbuf(),or
  putback()/unget() is called on a stream with a null rdbuf(),or a
  null pointer passed to operator<<(basic_streambuf*)

• rdbuf()->sputbackc() or rdbuf()->sungetc() return traits::eof() to
  putback() orunget()`

• rdbuf()->pubsync() returns -1 to sync(),to flush(),or to the
  destructor of ostream::sentry on a unitbuf stream

• Exception is thrown during an I/O operation by any member function of
  the associated stream buffer (e.g. sbumpc(),xsputn(),sgetc(),
  overflow(),etc)

• Exception is thrown in iword() or pword() (e.g. std::bad_alloc)

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