c++ - C++11 Exception's destructor allows to throw now? -


any idea why virtual ~exception() throw() in c++98, virtual ~exception() in c++11?

what's design decision allows c++11 throw in destructor of class exception?

from here:

c++98:

class exception { public:   exception () throw();   exception (const exception&) throw();   exception& operator= (const exception&) throw();   virtual ~exception() throw();   virtual const char* what() const throw(); }

c++11:

class exception { public:   exception () noexcept;   exception (const exception&) noexcept;   exception& operator= (const exception&) noexcept;   virtual ~exception();   virtual const char* what() const noexcept; }

what's desing decision makes c++11 allow throw in destructor of class exception?

there no such design decision (fortunately!). in c++11, explicitly declared destructors qualified noexcept default. can evinced paragraph 12.4/3 of c++11 standard:

a declaration of destructor not have exception-specification implicitly considered have same exception-specification implicit declaration (15.4).

and paragraph 15.4/14, specifies exception specification implicit declaration has:

an inheriting constructor (12.9) , implicitly declared special member function (clause 12) have exception-specification. if f inheriting constructor or implicitly declared default constructor, copy constructor, move constructor, destructor, copy assignment operator, or move assignment operator, implicit exception-specification specifies type-id t if , if t allowed exception-specification of function directly invoked f’s implicit definition; f allows exceptions if function directly invokes allows exceptions, , f has exception-specification noexcept(true) if every function directly invokes allows no exceptions.

together, above 2 paragraphs guarantee (given declaration quoted of exception's destructor) destructor of exception won't throw.

this explicitly stated in paragraphs 18.8.1/7-8 of c++11 standard:

virtual ~exception();

7 effects: destroys object of class exception.

8 remarks: does not throw exceptions.

notice, dynamic exception specifications (such throw()) deprecated in c++11. per § d.4/1 of annex d:

the use of dynamic-exception-specifications deprecated.


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