1) The copy assignment operator is protected, and is deleted. Output streams are notCopyAssignable.

2) The move assignment operator exchanges all data members of the base class, except forrdbuf(), withrhs, as if by callingswap(*rhs). This move assignment operator is protected: it is only called by the move assignment operators of the derived movable output stream classesstd::basic_ofstream andstd::basic_ostringstream, which know how to correctly move-assign the associated streambuffers.

#include <iostream>#include <sstream>#include <utility> int main(){std::ostringstream s;//  std::cout = s;            // ERROR: copy assignment operator is deleted//  std::cout = std::move(s); // ERROR: move assignment operator is protected    s= std::move(std::ostringstream()<<42);// OK, moved through derivedstd::cout<< s.str()<<'\n';}

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