C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  delete[] and exceptions in array element destructors          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message kib Guest Posted: Thu Apr 29, 2004 10:00 pm    Post subject: delete[] and exceptions in array element destructors The standard, 15.2, paragraph 2 says An object that is partially constructed or partially destroyed will have destructors executed for all of its fully constructed subobjects, that is, for subobjects for which the constructor has completed execution and the destructor has not yet begun execution. I read this as requirement for delete[] x to call the destructors of all elements x, even if some destructor of x[i] raises exception in the course of action. Is this true ? The following test program #include <iostream> class A { public: static int c; A(); ~A(); void f(); }; int A::c = 0; A::A() { c++; std::cerr << "Constructing " << c << std::endl; } A::~A() { std::cerr << "Destructing " << c << std::endl; c--; if (c == 5) throw 5; } void A::f() { std::cerr << "A::f()" << std::endl; } int main() { try { A a[10]; a[10].f(); } catch (int& i) { std::cerr << "Caught " << i << std::endl; } return 0; } was run under g++ 3.4.0, Sun C++ 5.5 2003/03/12 and MS VC++ (.NET 2003) 13.10.3077. For gcc and CC, I got Constructing 1 Constructing 2 Constructing 3 Constructing 4 Constructing 5 Constructing 6 Constructing 7 Constructing 8 Constructing 9 Constructing 10 A::f() Destructing 10 Destructing 9 Destructing 8 Destructing 7 Destructing 6 Caught 5 For VC++, Constructing 1 Constructing 2 Constructing 3 Constructing 4 Constructing 5 Constructing 6 Constructing 7 Constructing 8 Constructing 9 Constructing 10 A::f() Destructing 10 Destructing 9 Destructing 8 Destructing 7 Destructing 6 Destructing 5 Destructing 4 Destructing 3 Destructing 2 Destructing 1 Caught 5 If my claim true, then gcc and CC do not conform to this standard clause, and VC++ conforms, isn't it ? [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Paul D. DeRocco Guest Posted: Fri Apr 30, 2004 11:26 am    Post subject: Re: delete[] and exceptions in array element destructors Quote: "kib" <kostikbel (AT) ukr (DOT) net> wrote The standard, 15.2, paragraph 2 says An object that is partially constructed or partially destroyed will have destructors executed for all of its fully constructed subobjects, that is, for subobjects for which the constructor has completed execution and the destructor has not yet begun execution. I read this as requirement for delete[] x to call the destructors of all elements x, even if some destructor of x[i] raises exception in the course of action. Is this true ? That's a bit too lawyerly for me. However, if you allow your destructors to throw exceptions, then I have no sympathy for your plight. ;-) -- Ciao, Paul D. DeRocco Paul mailto:pderocco (AT) ix (DOT) netcom.com [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze@gabi-soft.fr Guest Posted: Sat May 01, 2004 2:58 am    Post subject: Re: delete[] and exceptions in array element destructors [email]kostikbel (AT) ukr (DOT) net[/email] (kib) wrote in message news:<1629a38d.0404290257.2c521d43 (AT) posting (DOT) google.com>... Quote: The standard, 15.2, paragraph 2 says An object that is partially constructed or partially destroyed will have destructors executed for all of its fully constructed subobjects, that is, for subobjects for which the constructor has completed execution and the destructor has not yet begun execution. I read this as requirement for delete[] x to call the destructors of all elements x, even if some destructor of x[i] raises exception in the course of action. Is this true ? Yes. Of course, if two or more of the destructors raises an exception, the implementation should call terminate. Quote: If my claim true, then gcc and CC do not conform to this standard clause, and VC++ conforms, isn't it ? That's what it looks like. -- James Kanze GABI Software mailto:kanze (AT) gabi-soft (DOT) fr Conseils en informatique orientée objet/ http://www.gabi-soft.fr Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Vladimír Marko Guest Posted: Sat May 01, 2004 12:07 pm    Post subject: Re: delete[] and exceptions in array element destructors "kib" <kostikbel (AT) ukr (DOT) net> wrote Quote: The standard, 15.2, paragraph 2 says An object that is partially constructed or partially destroyed will have destructors executed for all of its fully constructed subobjects, that is, for subobjects for which the constructor has completed execution and the destructor has not yet begun execution. I read this as requirement for delete[] x to call the destructors of all elements x, even if some destructor of x[i] raises exception in the course of action. Is this true ? The following test program [snip] If my claim true, then gcc and CC do not conform to this standard clause, and VC++ conforms, isn't it ? I guess the intent is to have all created objects destroyed, but I found nothing that would describe that specific case in standard. The next sentence in the paragraph you quoted says "Should a constructor for an element of an automatic array throw an exception, only the constructed elements of that array will be destroyed." and something similar should be applied to throwing in the destructor, but it is NOT present in 15.2. The fact that the standard explicitly mentions throw from array element constructor and fails to mention throw from array element destructor could be seen as a defect. Try to post it to comp.std.c++. However, when a dtor of an array element throws, we have a lose-lose situation. g++ chooses not to call the dtors for the remaining elements which will often result into some resource leaks. On the other hand, VC++ tries to call the dtors and runs a very real risk of calling std::terminate() if another dtor throws. While I believe that the second behaviour is correct, this should be only an academic issue. Programmers should follow the well meant note in 15.2/3: "So destructors should generally catch exceptions and not let them propagate out of the destructor." Vladimir Marko [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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