Question

In C++, each stream has a bad bit:

This flag is set by operations performed on the stream when an error occurs while read or writing data, generally causing the loss of integrity of the stream.

Source

What would cause a stream to “lose integrity” and enter the bad state? This is not the same as the fail state, which most often occurs when an input stream attempts to store a value into a variable that cannot accept said value (such as attempting to store a string into an integer variable).

Note that this question is a more general form of c++ file bad bit, which is specific to file input streams; this question is not an exact duplicate as it applies to both input and output streams in general.

Answer 1

According to cppreference.com :

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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