C++ Programming :: Address of vector question


	Address of vector question I recently have upgraded compilers and my new one enables iterator checking. When a vector is empty, &v[0] blows up, as it should I guess. In replacing these I have been torn in using &v.begin() or &v.front() Does anyone prefer one over the other? Why? On 29 Maj, 16:30, McGragger <shawn.gr@gmail.com> wrote: > I recently have upgraded compilers and my new one enables iterator > checking. When a vector is empty, &v[0] blows up, as it should I > guess. In replacing these I have been torn in using > &v.begin() or &v.front() > Does anyone prefer one over the other? Why? I'd use front() since you then don't create a new iterator on each call. I hope you are aware of the fact that that &front() is no better than &v[0] if the vector is empty, and remember the vector may relocate after any insert. -- Erik Wikstrm On 29 Maj, 16:36, Erik Wikstrm <eri@student.chalmers.se> wrote: > On 29 Maj, 16:30, McGragger <shawn.gr@gmail.com> wrote: > > I recently have upgraded compilers and my new one enables iterator > > checking. When a vector is empty, &v[0] blows up, as it should I > > guess. In replacing these I have been torn in using > > &v.begin() or &v.front() > > Does anyone prefer one over the other? Why? > I'd use front() since you then don't create a new iterator on each > call. I hope you are aware of the fact that that &front() is no better > than &v[0] if the vector is empty, and remember the vector may > relocate after any insert. Actually, on my platform (VS2005) front() is implemented as 'return begin();', so it's about as efficient as &v.begin(). This, of course, is implementation dependant. -- Erik Wikstrm On May 29, 10:40 am, Erik Wikstrm <eri@student.chalmers.se> wrote: - Hide quoted text - > On 29 Maj, 16:36, Erik Wikstrm <eri@student.chalmers.se> wrote: > > On 29 Maj, 16:30, McGragger <shawn.gr@gmail.com> wrote: > > > I recently have upgraded compilers and my new one enables iterator > > > checking. When a vector is empty, &v[0] blows up, as it should I > > > guess. In replacing these I have been torn in using > > > &v.begin() or &v.front() > > > Does anyone prefer one over the other? Why? > > I'd use front() since you then don't create a new iterator on each > > call. I hope you are aware of the fact that that &front() is no better > > than &v[0] if the vector is empty, and remember the vector may > > relocate after any insert. > Actually, on my platform (VS2005) front() is implemented as 'return > begin();', so it's about as efficient as &v.begin(). This, of > course, is implementation dependant. > -- > Erik Wikstrm I am aware of the bigger issue here but I am simply trying to upgrade code that has worked for a very long time. Thanks for your reply. I think &v.front() is a little more natural. "Erik Wikstrm" < I hope you are aware of the fact that that &front() is no better than &v[0] if the vector is empty, There is 1 less function call parameter with front(). Posted Via Usenet.com Premium Usenet Newsgroup Services ---------------------------------------------------------- SPEED RETENTION COMPLETION ANONYMITY ** ---------------------------------------------------------- http://www.usenet.com McGragger wrote: > I recently have upgraded compilers and my new one enables iterator > checking. When a vector is empty, &v[0] blows up, as it should I > guess. In replacing these I have been torn in using > &v.begin() or &v.front() > Does anyone prefer one over the other? Why? When vector is empty v.begin() equals to v.end() and you know you should never dereference v.end() right? (ie v.begin() when v.empty() is UB). v.front() has the same problem when v.empty() it's UB. What is the correct version? Well something along the lines of: "v.empty()?0:&v[0]" (that assuming that you want to get a 0/NULL pointer when v is empty). -- Dizzy On 2007-05-29 07:30:31 -0700, McGragger <shawn.gr@gmail.com> said: > I recently have upgraded compilers and my new one enables iterator > checking. When a vector is empty, &v[0] blows up, as it should I > guess. If the vector is empty, then all of these invoke undefined behavior, and should not be used. > In replacing these I have been torn in using > &v.begin() or &v.front() > Does anyone prefer one over the other? Why? Either check to make sure that the vector isn't empty first: v.empty()?NULL:&v.front() or use &v.at(0) and deal with the exception that it can throw. -- Clark S. Cox III clarkc@gmail.com On 29 Maj, 16:30, McGragger <shawn.gr@gmail.com> wrote: > I recently have upgraded compilers and my new one enables iterator > checking. When a vector is empty, &v[0] blows up, as it should I > guess. In replacing these I have been torn in using > &v.begin() or &v.front() > Does anyone prefer one over the other? Why? Use what Clark Cox suggests - or use v.data() which will do the same thing. Unfortunately, this one is only available in C++ 0x unless I'm mistaken, so your compiler might not yet support it. /Peter