std::ios_base:: operator=

From cppreference.com
private :
ios_base & operator = ( const ios_base & ) ;
(until C++11)
public :
ios_base & operator = ( const ios_base & ) = delete ;
(since C++11)

The copy assignment operator is private (until C++11) deleted (since C++11) : streams are not copy-assignable.

Defect reports

The following behavior-changing defect reports were applied retroactively to previously published C++ standards.

DR Applied to Behavior as published Correct behavior
LWG 50 C++98 the copy assignment operator was not specified specified as private