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Message: [QUOTE="john, post: 3057298"] I am reading TC++PL3 and in 21.3.8 it describes the class sentry, which is member of basic_istream and basic_ostream. Q1: Should we always use the sentry class when we define new functions and operators for basic_ostream/basic_istream (ostream/istream)? Q2: It is mentioned that we can place code "such as throwing exceptions caused by state changes" in the sentry's destructor. However in 14.4.7 it is mentioned: "Exiting from a destructor by throwing an exception is also a violation of the standard library requirements (E2)". I suppose both sentry's constructor and destructor, are to be provided by the implementer of the standard library basic_istream and basic_ostream classes? [/QUOTE]