C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Can you overload operator delete?          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Matthias Hofmann Guest Posted: Sat Oct 18, 2003 11:14 pm    Post subject: Can you overload operator delete? Hello, I know that operator new can be overload, e.g. as follows: void* operator new( size_t size, const char* file, int line ); But how is it with operator delete? If I declare void operator delete( void* p, const char* file, int line ); how do I make the compiler use it? int main() { int* p = new( __FILE__, __LINE__ ) int; // Works fine delete( __FILE__, __LINE__ ) p; // Error return 0; } VC++ 6.0 rejects the call to operator delete from above - what can I do? Regards, Matthias [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Christoph Schulz Guest Posted: Sun Oct 19, 2003 10:32 am    Post subject: Re: Can you overload operator delete? Hello! Matthias Hofmann <hofmann (AT) anvil-soft (DOT) com> wrote: Quote: Hello, I know that operator new can be overload, e.g. as follows: void* operator new( size_t size, const char* file, int line ); But how is it with operator delete? If I declare void operator delete( void* p, const char* file, int line ); how do I make the compiler use it? You cannot pass arguments when using the operator syntax. But you can call it as a function: int *p = new int (__FILE__, __LINE__); operator delete (p, __FILE__, __LINE__); Normally, you *only* overload the delete operator to match an existing new operator. This is done for exception safety: If the constructor for an object being created by "operator new" throws an exception, the memory for the object is /only/ released if a matching and accessible "operator delete" declaration is found. Note that your declaration of "delete" does not match your "new" operator, because it is missing "size_t" as the second parameter. See 5.3.4/19 and /20. The reason why you typically don't want to overload operator delete for any other reason as mentioned above is that you probably don't have much information about the object to be destroyed at destruction time. That means that you typically don't know how the object has been created, so how you are supposed to choose the "right" deallocation operator? This is why destructors in C++ don't have parameters: the caller of a destructor (using operator delete) is not expected to know the complete type of the object which is destroyed (think of polymorphic use where you only have a pointer to a base class), so how can the caller be expected to be able to supply the "right" destructor arguments? Regards, Christoph [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dhruv Guest Posted: Sun Oct 19, 2003 6:41 pm    Post subject: Re: Can you overload operator delete? On Sat, 18 Oct 2003 19:14:09 -0400, Matthias Hofmann wrote: Quote: Hello, I know that operator new can be overload, e.g. as follows: void* operator new( size_t size, const char* file, int line ); But how is it with operator delete? If I declare void operator delete( void* p, const char* file, int line ); how do I make the compiler use it? int main() { int* p = new( __FILE__, __LINE__ ) int; // Works fine //Destroy contents of p if it is of a non-trivial or Non-Pod type. operator delete(p, __FILE__, __LINE__ ); Quote: return 0; } Regards, -Dhruv. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Matthias Hofmann Guest Posted: Mon Oct 20, 2003 9:06 pm    Post subject: Re: Can you overload operator delete? Christoph Schulz <kristov (AT) arcor (DOT) de> schrieb in im Newsbeitrag: bmt843$pkmau$1 (AT) ID-175807 (DOT) news.uni-berlin.de... Quote: Hello! Matthias Hofmann <hofmann (AT) anvil-soft (DOT) com> wrote: Hello, I know that operator new can be overload, e.g. as follows: void* operator new( size_t size, const char* file, int line ); But how is it with operator delete? If I declare void operator delete( void* p, const char* file, int line ); how do I make the compiler use it? You cannot pass arguments when using the operator syntax. But you can call it as a function: int *p = new int (__FILE__, __LINE__); operator delete (p, __FILE__, __LINE__); Normally, you *only* overload the delete operator to match an existing new operator. This is done for exception safety: If the constructor for an object being created by "operator new" throws an exception, the memory for the object is /only/ released if a matching and accessible "operator delete" declaration is found. Oh, I see. I have to provide an additional void operator delete( void* ); Quote: Note that your declaration of "delete" does not match your "new" operator, because it is missing "size_t" as the second parameter. See 5.3.4/19 and /20. This section tells me that the operators match if all arguments except for the first one are identical. Therefore, I think that my declaration of "delete" actually does match my "new" operator. Regards, Matthias [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Christoph Schulz Guest Posted: Tue Oct 21, 2003 3:45 pm    Post subject: Re: Can you overload operator delete? Hello! Matthias Hofmann <hofmann (AT) anvil-soft (DOT) com> wrote: Quote: Christoph Schulz <kristov (AT) arcor (DOT) de> schrieb in im Newsbeitrag: bmt843$pkmau$1 (AT) ID-175807 (DOT) news.uni-berlin.de... Note that your declaration of "delete" does not match your "new" operator, because it is missing "size_t" as the second parameter. See 5.3.4/19 and /20. This section tells me that the operators match if all arguments except for the first one are identical. Therefore, I think that my declaration of "delete" actually does match my "new" operator. You're right. The special handling of the size_t parameter does only apply to non-placement deallocation functions. Sorry for the wrong information I gave you. Regards, Christoph [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Matthias Hofmann Guest Posted: Wed Oct 22, 2003 6:39 pm    Post subject: Re: Can you overload operator delete? Christoph Schulz <kristov (AT) arcor (DOT) de> schrieb in im Newsbeitrag: bn1j2c$s7v02$1 (AT) ID-175807 (DOT) news.uni-berlin.de... Quote: Hello! Matthias Hofmann <hofmann (AT) anvil-soft (DOT) com> wrote: Christoph Schulz <kristov (AT) arcor (DOT) de> schrieb in im Newsbeitrag: bmt843$pkmau$1 (AT) ID-175807 (DOT) news.uni-berlin.de... Note that your declaration of "delete" does not match your "new" operator, because it is missing "size_t" as the second parameter. See 5.3.4/19 and /20. This section tells me that the operators match if all arguments except for the first one are identical. Therefore, I think that my declaration of "delete" actually does match my "new" operator. You're right. The special handling of the size_t parameter does only apply to non-placement deallocation functions. Sorry for the wrong information I gave you. What special handling do you mean? Can you point me to the corresponding section in the standard? Regards, Matthias [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Christoph Schulz Guest Posted: Thu Oct 23, 2003 11:21 am    Post subject: Re: Can you overload operator delete? Hello! Matthias Hofmann <hofmann (AT) anvil-soft (DOT) com> wrote: Quote: Christoph Schulz <kristov (AT) arcor (DOT) de> schrieb in im Newsbeitrag: bn1j2c$s7v02$1 (AT) ID-175807 (DOT) news.uni-berlin.de... Hello! Matthias Hofmann <hofmann (AT) anvil-soft (DOT) com> wrote: Christoph Schulz <kristov (AT) arcor (DOT) de> schrieb in im Newsbeitrag: bmt843$pkmau$1 (AT) ID-175807 (DOT) news.uni-berlin.de... Note that your declaration of "delete" does not match your "new" operator, because it is missing "size_t" as the second parameter. See 5.3.4/19 and /20. This section tells me that the operators match if all arguments except for the first one are identical. Therefore, I think that my declaration of "delete" actually does match my "new" operator. You're right. The special handling of the size_t parameter does only apply to non-placement deallocation functions. Sorry for the wrong information I gave you. What special handling do you mean? Can you point me to the corresponding section in the standard? I mean only that operator delete (void*, size_t) matches operator new (size_t) although the parameter lists are not the same (excluding the first parameter). This is because "any non-placement deallocation matches a non-placement allocation function" (5.3.4/19). Regards, Christoph [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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