ios_base( const ios_base& );
1) The copy constuctor is deleted: streams are not copyable
2) The default constructor is protected: only derived classes may construct
std::ios_base. The internal state is undefined after the construction. The derived class must call basic_ios::init() to complete initialization before first use or before destructor, otherwise the behavior is undefined.
The same applies to the constructors of the next class in the I/O hierarchy, std::basic_ios. Further-derived classes (std::istream and std::ostream) are always constructed with a concrete streambuffer object and call basic_ios::init(), possibly more than once, to complete initialization of their virtual base.