cpp/io/basic ios/init

Sets the associated stream buffer to and initializes the internal state.

The postconditions are as follows:

This member function is protected: it is called by the constructors of the derived stream classes std and std once the associated stream buffer is known. Until this function is called, every member function (including the destructor) of the default-constructed std invokes undefined behavior. Note that is a virtual base class, and therefore its constructor is not called by the constructors of those directly derived classes, which is why two-stage initialization is necessary.