std::ios_base::operator=

private:
ios_base& operator=( const ios_base& );

public:
ios_base& operator=( const ios_base& ) = delete;

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.