C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Passing refrences to objects...          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message JustSomeGuy Guest Posted: Tue Jun 29, 2004 5:28 pm    Post subject: Passing refrences to objects... Silly question maybe... I pass a refrence to an object to a method... The method adds the object to a (stl) list of these objects... However if a refrence to the object is passed and then added list... if the original object is destroyed.. is the object in the list invalid or is a copy of the object made by the stl list for insertion purposes Back to top Rolf Magnus Guest Posted: Tue Jun 29, 2004 5:44 pm    Post subject: Re: Passing refrences to objects... JustSomeGuy wrote: Quote: Silly question maybe... I pass a refrence to an object to a method... The method adds the object to a (stl) list of these objects... However if a refrence to the object is passed and then added list... if the original object is destroyed.. is the object in the list invalid or is a copy of the object made by the stl list for insertion purposes The list contains a copy of the object, so destroying the original won't affect the list. Back to top Chris Theis Guest Posted: Tue Jun 29, 2004 5:44 pm    Post subject: Re: Passing refrences to objects... "JustSomeGuy" <NoOne (AT) ucalgary (DOT) ca> wrote Quote: Silly question maybe... I pass a refrence to an object to a method... The method adds the object to a (stl) list of these objects... However if a refrence to the object is passed and then added list... if the original object is destroyed.. is the object in the list invalid or is a copy of the object made by the stl list for insertion purposes In the container classes of the standard library copies of the passed objects are inserted. But you can easily try & check this yourself. HTH Chris Back to top Bob Hairgrove Guest Posted: Tue Jun 29, 2004 6:02 pm    Post subject: Re: Passing refrences to objects... On Tue, 29 Jun 2004 11:28:09 -0600, JustSomeGuy <NoOne (AT) ucalgary (DOT) ca> wrote: Quote: Silly question maybe... I pass a refrence to an object to a method... The method adds the object to a (stl) list of these objects... However if a refrence to the object is passed and then added list... if the original object is destroyed.. is the object in the list invalid or is a copy of the object made by the stl list for insertion purposes You cannot create containers of references, only of objects or pointers. If you allocate memory for an object with "new" and store a pointer to that object in an STL container, you need to ensure that you call "delete" on every pointer before the container is cleared. -- Bob Hairgrove [email]NoSpamPlease (AT) Home (DOT) com[/email] Back to top Chris Theis Guest Posted: Tue Jun 29, 2004 7:42 pm    Post subject: Re: Passing refrences to objects... "Bob Hairgrove" <wouldnt_you_like (AT) to_know (DOT) com> wrote [SNIP] Quote: If you allocate memory for an object with "new" and store a pointer to that object in an STL container, you need to ensure that you call "delete" on every pointer before the container is cleared. This is not necessarily true. The standard library containers also create copies of pointers and it depends very much what you want to achieve whether a delete statement should/must be issued before the container is cleared. Imagine for example a container of pointers to geometric primitives and another container where you store the pointers to the subset of the primitives that have been selected. If you called a delete statement on the pointers in the selection container then you´d send all those primitives into nirvana which is certainly not what you normally would want. Cheers Chris Back to top Bob Hairgrove Guest Posted: Tue Jun 29, 2004 7:47 pm    Post subject: Re: Passing refrences to objects... On Tue, 29 Jun 2004 21:42:34 +0200, "Chris Theis" <Christian.Theis (AT) nospam (DOT) cern.ch> wrote: Quote: "Bob Hairgrove" <wouldnt_you_like (AT) to_know (DOT) com> wrote in message news:5ib3e0976l2jmerpusv2co1jq6ausm5ttn (AT) 4ax (DOT) com... [SNIP] If you allocate memory for an object with "new" and store a pointer to that object in an STL container, you need to ensure that you call "delete" on every pointer before the container is cleared. This is not necessarily true. The standard library containers also create copies of pointers and it depends very much what you want to achieve whether a delete statement should/must be issued before the container is cleared. Imagine for example a container of pointers to geometric primitives and another container where you store the pointers to the subset of the primitives that have been selected. If you called a delete statement on the pointers in the selection container then you´d send all those primitives into nirvana which is certainly not what you normally would want. You are quite correct ... of course, it is a question of who "owns" the memory allocated for the pointers. In most cases I have seen, it will be whatever is controlling the container, though (or perhaps some other container higher up in a certain application-defined hierarchy, as you suggest). The OP's question seemed to indicate that it was an issue to be pointed out. -- Bob Hairgrove [email]NoSpamPlease (AT) Home (DOT) com[/email] Back to top Display posts from previous: All Posts1 Day7 Days2 Weeks1 Month3 Months6 Months1 Year Oldest FirstNewest First         C++Talk.NET Forum Index -> C++ language (comp.lang.c++) All times are GMT Page 1 of 1   Jump to: Select a forum C/C++----------------C LanguageC Language (Moderated)C++ Language (Moderated)C++ language (comp.lang.c++)C++ language, library and standards Non-English C/C++ Newsgroups----------------C++ (German)C++ (French)  You cannot post new topics in this forum You cannot reply to topics in this forum You cannot edit your posts in this forum You cannot delete your posts in this forum You cannot vote in polls in this forum Powered by phpBB © 2001, 2006 phpBB Group SEO toolkit © 2004-2006 webmedic.