C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  iterators          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message slurper Guest Posted: Fri Oct 22, 2004 3:42 pm    Post subject: iterators i have problems with following piece of code vector<job> jobvector; (i put some jobs in this vector) list<job*> joblist; void copy_vector_into_list() { vector<job>::iterator iter = jobvector.begin(); for ( iter; iter != jobvector.end(); ++iter ) { joblist.push_back(iter); } } what i want: i have a vector of jobs i want to add the jobs to the list also, but to avoid a copy of the job, i want to use pointers to jobs, so that no copies for jobs need to be made. but there seems to be a problem iter is vector<job>::iterator. i want to do a push_back on the list of the job pointed to by the iterator. how should i do this?? casting? but how? i make the copy (of pointers) because i want to manipulate the list and keep the vector. tx for help Back to top Victor Bazarov Guest Posted: Fri Oct 22, 2004 3:55 pm    Post subject: Re: iterators slurper wrote: Quote: i have problems with following piece of code vector<job> jobvector; (i put some jobs in this vector) list<job*> joblist; void copy_vector_into_list() { vector<job>::iterator iter = jobvector.begin(); for ( iter; iter != jobvector.end(); ++iter ) { joblist.push_back(iter); } } what i want: i have a vector of jobs i want to add the jobs to the list also, but to avoid a copy of the job, i want to use pointers to jobs, so that no copies for jobs need to be made. Bad idea. Addresses of elements of std::vector are probably the most unreliable thing in C++. The vector's storage can change easily and your pointers will become invalid. Quote: but there seems to be a problem iter is vector<job>::iterator. i want to do a push_back on the list of the job pointed to by the iterator. how should i do this?? casting? but how? No, not casting. The dereferencing operator (operator*) for an iterator yields a reference to the object. Taking address will give you the pointer to the object. Iterators are not pointers. joblist.push_back(&(*iter)); Quote: i make the copy (of pointers) because i want to manipulate the list and keep the vector. Well, that's up to you, of course. V Back to top Jeff Flinn Guest Posted: Fri Oct 22, 2004 3:57 pm    Post subject: Re: iterators "slurper" <slurper1234 (AT) hotmail (DOT) com> wrote Quote: i have problems with following piece of code vector<job> jobvector; (i put some jobs in this vector) list<job*> joblist; void copy_vector_into_list() { vector<job>::iterator iter = jobvector.begin(); for ( iter; iter != jobvector.end(); ++iter ) { joblist.push_back(iter); joblist.push_back(&(*iter)); Quote: } } Beware that these addresses can become invalidated whenever jobs are added or removed from jobvector. It's better to use smart pointers in both cases. Using boost::shared_ptr from www.boost.org: typedef boost::shared_ptr<job> tJobPtr; std::vector<tjobPtr> jobvector; std::list<tJobPtr> joblist; jobvector.push_back( tJobPtr(new Job) ); .... std::copy( jobvector.begin(), jobvector.end(), std::back_inserter( joblist ) ); Jeff F Back to top Richard Herring Guest Posted: Fri Oct 22, 2004 4:10 pm    Post subject: Re: iterators In message <41792ae8$0$22757$ba620e4c (AT) news (DOT) skynet.be>, slurper <slurper1234 (AT) hotmail (DOT) com> writes Quote: i have problems with following piece of code vector<job> jobvector; (i put some jobs in this vector) list<job*> joblist; void copy_vector_into_list() { vector<job>::iterator iter = jobvector.begin(); for ( iter; iter != jobvector.end(); ++iter ) { joblist.push_back(iter); } } what i want: i have a vector of jobs i want to add the jobs to the list also, but to avoid a copy of the job, i want to use pointers to jobs, so that no copies for jobs need to be made. Think about the problem more abstractly. You want to use something which _behaves like_ a pointer. It doesn't have to _be_ a pointer. Quote: but there seems to be a problem iter is vector<job>::iterator. i want to do a push_back on the list of the job pointed to by the iterator. No, since you don't want to copy the jobs, you want to push_back something which acts like a pointer. Quote: how should i do this?? casting? but how? i make the copy (of pointers) because i want to manipulate the list and keep the vector. So make the list of vector iterators instead of pointers: list<vector joblist; (And remember that you must not perform any operations on the vector which will invalidate the iterators.) -- Richard Herring Back to top Evan Carew Guest Posted: Thu Oct 28, 2004 11:30 pm    Post subject: Re: iterators -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 slurper wrote: Quote: i have problems with following piece of code vector<job> jobvector; (i put some jobs in this vector) list<job*> joblist; void copy_vector_into_list() { vector<job>::iterator iter = jobvector.begin(); for ( iter; iter != jobvector.end(); ++iter ) { joblist.push_back(iter); } } what i want: i have a vector of jobs i want to add the jobs to the list also, but to avoid a copy of the job, i want to use pointers to jobs, so that no copies for jobs need to be made. but there seems to be a problem iter is vector<job>::iterator. i want to do a push_back on the list of the job pointed to by the iterator. how should i do this?? casting? but how? i make the copy (of pointers) because i want to manipulate the list and keep the vector. Slurper, Also watch out for the memory leak issue when using raw pointers & the STL. By default, the STL is designed with object ownership in mind. This ensures that when a container either goes out of scope, or is explicitly deleted, all contained objects are also cleaned up. In the case of storing pointers to objects in the containers, you are responsible for cleanup yourself. To address this well known problem (feature), a special type of "pointer" was developed called "smart pointers" (see the boost's http://boost.org/libs/smart_ptr/smart_ptr.htm for more info). These pointers, in turn, delete the objects stored on the heap which you don't want to copy into the container when appropriate. Evan -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.0.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFBgYD5oo/Prlj9GScRApswAJ94RPqPoCv9tCgQlT4YTwR2W1P1qQCcCVDn xVmvx/BPKzg9fThNN4KIMSA= =eIBi -----END PGP SIGNATURE----- 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.