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operator< for algorithms
Hello,
namespace NS1 { namespace NS2 { template <typename T1, typename T2> class C { public: typedef T1::xType xType; typedef T1::yType yType; .... private: typedef std::pair< xType, yType> EntryType; boost::array< EntryType , size > ContainerType; .... }; .... }} I need to use std::lower_bound and sorting algorithms on my ContainerType. Where (which namespace) and how can I define the operator< comparing 2 EntryType for the std:: algorithms to use that operator? Note I use these std::algorithms only in member functions of the C template. So I wish to define the operator< in a way that is specific and visible only to C template. best regards, |
Re: operator< for algorithms
Hicham Mouline wrote:
> namespace NS1 { namespace NS2 { > > template <typename T1, typename T2> > class C { > public: > typedef T1::xType xType; > typedef T1::yType yType; > ... > private: > typedef std::pair< xType, yType> EntryType; > boost::array< EntryType , size > ContainerType; > .... > }; > ... > }} > > I need to use std::lower_bound and sorting algorithms on my ContainerType. > > Where (which namespace) and how can I define the operator< comparing 2 > EntryType > for the std:: algorithms to use that operator? Anywhere appropriate. Any namespace/class where your compiler is capable of finding it. > Note I use these std::algorithms only in member functions of the C template. > So I wish to define the operator< in a way that is specific and visible only > to C template. Have you tried defining it as a static member of the C template? Post the rest of your code, with only the operator< missing, and we can probably figure it out. I am just too lazy to provide all the necessary driver code for what you've described, I consider it your job if you want my help. Sorry, such a PITA I am. V -- Please remove capital 'A's when replying by e-mail I do not respond to top-posted replies, please don't ask |
Re: operator< for algorithms
"Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message
news:gr2bjd$st4$1@news.datemas.de... > Hicham Mouline wrote: >> namespace NS1 { namespace NS2 { >> >> template <typename T1, typename T2> >> class C { >> public: >> typedef T1::xType xType; >> typedef T1::yType yType; >> ... >> private: >> typedef std::pair< xType, yType> EntryType; >> boost::array< EntryType , size > ContainerType; >> .... >> }; >> ... >> }} >> >> I need to use std::lower_bound and sorting algorithms on my >> ContainerType. >> >> Where (which namespace) and how can I define the operator< comparing 2 >> EntryType >> for the std:: algorithms to use that operator? > > Anywhere appropriate. Any namespace/class where your compiler is capable > of finding it. > >> Note I use these std::algorithms only in member functions of the C >> template. >> So I wish to define the operator< in a way that is specific and visible >> only to C template. > > Have you tried defining it as a static member of the C template? > > Post the rest of your code, with only the operator< missing, and we can > probably figure it out. I am just too lazy to provide all the necessary > driver code for what you've described, I consider it your job if you want > my help. Sorry, such a PITA I am. > > V Not at all. Thank you for your contrib! I put the code here http://codepad.org/Gwfm36GL It fails to compile under g++4 "operator< needs to be must be either a non-static member function or a non-member function" if it is member non-static, it is interpreted as applying to C<T1,T2> not to EntryType As EntryType is private, I don't know how to define outside of C<T1,T2> rds, |
Re: operator< for algorithms
Hicham Mouline wrote:
> "Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message > news:gr2bjd$st4$1@news.datemas.de... >> Hicham Mouline wrote: >>> namespace NS1 { namespace NS2 { >>> >>> template <typename T1, typename T2> >>> class C { >>> public: >>> typedef T1::xType xType; >>> typedef T1::yType yType; >>> ... >>> private: >>> typedef std::pair< xType, yType> EntryType; >>> boost::array< EntryType , size > ContainerType; >>> .... >>> }; >>> ... >>> }} >>> >>> I need to use std::lower_bound and sorting algorithms on my >>> ContainerType. >>> >>> Where (which namespace) and how can I define the operator< comparing 2 >>> EntryType >>> for the std:: algorithms to use that operator? >> Anywhere appropriate. Any namespace/class where your compiler is capable >> of finding it. >> >>> Note I use these std::algorithms only in member functions of the C >>> template. >>> So I wish to define the operator< in a way that is specific and visible >>> only to C template. >> Have you tried defining it as a static member of the C template? >> >> Post the rest of your code, with only the operator< missing, and we can >> probably figure it out. I am just too lazy to provide all the necessary >> driver code for what you've described, I consider it your job if you want >> my help. Sorry, such a PITA I am. >> >> V > Not at all. Thank you for your contrib! > > I put the code here > http://codepad.org/Gwfm36GL > > It fails to compile under g++4 > "operator< needs to be must be either a non-static member function or a > non-member function" > > if it is member non-static, it is interpreted as applying to C<T1,T2> not to > EntryType > > As EntryType is private, I don't know how to define outside of C<T1,T2> I managed to make your code from the 'codepad.org' to compile when I removed the operator< definition from the 'C' template (it wasn't the brightest suggestion, I guess) and put it right after the 'C' as this: template<class T, class U> bool operator<(const typename C<T,U>::EntryType& lhs, const typename C<T,U>::EntryType& rhs) { return true; } I am not sure how to try it with Comeau online. V -- Please remove capital 'A's when replying by e-mail I do not respond to top-posted replies, please don't ask |
Re: operator< for algorithms
"Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message news:gr2jto$g24$1@news.datemas.de... > Hicham Mouline wrote: >> "Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message >> news:gr2bjd$st4$1@news.datemas.de... >>> Hicham Mouline wrote: >>>> namespace NS1 { namespace NS2 { >>>> >>>> template <typename T1, typename T2> >>>> class C { >>>> public: >>>> typedef T1::xType xType; >>>> typedef T1::yType yType; >>>> ... >>>> private: >>>> typedef std::pair< xType, yType> EntryType; >>>> boost::array< EntryType , size > ContainerType; >>>> .... >>>> }; >>>> ... >>>> }} >>>> >>>> I need to use std::lower_bound and sorting algorithms on my >>>> ContainerType. >>>> >>>> Where (which namespace) and how can I define the operator< comparing 2 >>>> EntryType >>>> for the std:: algorithms to use that operator? >>> Anywhere appropriate. Any namespace/class where your compiler is >>> capable of finding it. >>> >>>> Note I use these std::algorithms only in member functions of the C >>>> template. >>>> So I wish to define the operator< in a way that is specific and visible >>>> only to C template. >>> Have you tried defining it as a static member of the C template? >>> >>> Post the rest of your code, with only the operator< missing, and we can >>> probably figure it out. I am just too lazy to provide all the necessary >>> driver code for what you've described, I consider it your job if you >>> want my help. Sorry, such a PITA I am. >>> >>> V >> Not at all. Thank you for your contrib! >> >> I put the code here >> http://codepad.org/Gwfm36GL >> >> It fails to compile under g++4 >> "operator< needs to be must be either a non-static member function or a >> non-member function" >> >> if it is member non-static, it is interpreted as applying to C<T1,T2> not >> to EntryType >> >> As EntryType is private, I don't know how to define outside of C<T1,T2> > > I managed to make your code from the 'codepad.org' to compile when I > removed the operator< definition from the 'C' template (it wasn't the > brightest suggestion, I guess) and put it right after the 'C' as this: > > template<class T, class U> > bool operator<(const typename C<T,U>::EntryType& lhs, > const typename C<T,U>::EntryType& rhs) > { > return true; > } It is strange that this compiles. EntryType is private, why does operator< outside manage to access it? Let me now see if that operator< is really used by lower_bound, rds, |
Re: operator< for algorithms
Hicham Mouline wrote:
> "Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message > news:gr2jto$g24$1@news.datemas.de... >> Hicham Mouline wrote: >>> "Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message >>> news:gr2bjd$st4$1@news.datemas.de... >>>> Hicham Mouline wrote: >>>>> namespace NS1 { namespace NS2 { >>>>> >>>>> template <typename T1, typename T2> >>>>> class C { >>>>> public: >>>>> typedef T1::xType xType; >>>>> typedef T1::yType yType; >>>>> ... >>>>> private: >>>>> typedef std::pair< xType, yType> EntryType; >>>>> boost::array< EntryType , size > ContainerType; >>>>> .... >>>>> }; >>>>> ... >>>>> }} >>>>> >>>>> I need to use std::lower_bound and sorting algorithms on my >>>>> ContainerType. >>>>> >>>>> Where (which namespace) and how can I define the operator< comparing 2 >>>>> EntryType >>>>> for the std:: algorithms to use that operator? >>>> Anywhere appropriate. Any namespace/class where your compiler is >>>> capable of finding it. >>>> >>>>> Note I use these std::algorithms only in member functions of the C >>>>> template. >>>>> So I wish to define the operator< in a way that is specific and visible >>>>> only to C template. >>>> Have you tried defining it as a static member of the C template? >>>> >>>> Post the rest of your code, with only the operator< missing, and we can >>>> probably figure it out. I am just too lazy to provide all the necessary >>>> driver code for what you've described, I consider it your job if you >>>> want my help. Sorry, such a PITA I am. >>>> >>>> V >>> Not at all. Thank you for your contrib! >>> >>> I put the code here >>> http://codepad.org/Gwfm36GL >>> >>> It fails to compile under g++4 >>> "operator< needs to be must be either a non-static member function or a >>> non-member function" >>> >>> if it is member non-static, it is interpreted as applying to C<T1,T2> not >>> to EntryType >>> >>> As EntryType is private, I don't know how to define outside of C<T1,T2> >> I managed to make your code from the 'codepad.org' to compile when I >> removed the operator< definition from the 'C' template (it wasn't the >> brightest suggestion, I guess) and put it right after the 'C' as this: >> >> template<class T, class U> >> bool operator<(const typename C<T,U>::EntryType& lhs, >> const typename C<T,U>::EntryType& rhs) >> { >> return true; >> } > It is strange that this compiles. > EntryType is private, why does operator< outside manage to access it? It is quite possible that since all instantiations of that operator are made from inside a member function of 'C', where access to 'EntryType' is granted, the compiler considers it an implicit permission... V -- Please remove capital 'A's when replying by e-mail I do not respond to top-posted replies, please don't ask |
Re: operator< for algorithms
"Victor Bazarov" <v.Abazarov@comAcast.net> wrote in message news:gr2kp5$i4s$1@news.datemas.de... >>> template<class T, class U> >>> bool operator<(const typename C<T,U>::EntryType& lhs, >>> const typename C<T,U>::EntryType& rhs) >>> { >>> return true; >>> } >> It is strange that this compiles. >> EntryType is private, why does operator< outside manage to access it? > > It is quite possible that since all instantiations of that operator are > made from inside a member function of 'C', where access to 'EntryType' is > granted, the compiler considers it an implicit permission... It doesn't seem to work template<class T, class U> bool operator<(const typename C<T,U>::EntryType& lhs, const typename C<T,U>::EntryType& rhs) { std::cout<< "called" <<std::endl; return true; } never prints anything I just realized c++03 defines operators< for std::pair<> in std. Maybe I need to override those rds, |
Re: operator< for algorithms
"Hicham Mouline" <hicham@mouline.org> wrote in message
news:49d4d773$0$90275$14726298@news.sunsite.dk... > It doesn't seem to work > > template<class T, class U> > bool operator<(const typename C<T,U>::EntryType& lhs, > const typename C<T,U>::EntryType& rhs) > { > std::cout<< "called" <<std::endl; > return true; > } > > never prints anything > > I just realized c++03 defines operators< for std::pair<> in std. > > Maybe I need to override those > > rds, still doesn't wor, strange http://codepad.org/h9uFoI1I rds, |
Re: operator< for algorithms
Hicham Mouline wrote:
> "Hicham Mouline" <hicham@mouline.org> wrote in message > news:49d4d773$0$90275$14726298@news.sunsite.dk... >> It doesn't seem to work >> >> template<class T, class U> >> bool operator<(const typename C<T,U>::EntryType& lhs, >> const typename C<T,U>::EntryType& rhs) >> { >> std::cout<< "called" <<std::endl; >> return true; >> } >> >> never prints anything >> >> I just realized c++03 defines operators< for std::pair<> in std. >> >> Maybe I need to override those >> >> rds, > > still doesn't wor, strange > http://codepad.org/h9uFoI1I Hm... I tried redefining your type 'EntryType' as derived from 'std::pair', and it didn't help either. I don't know. Apparently the compiler is unable to resolve it (or instantiate the template) and if falls back on what it can do, the operator < for std::pair... I think you should resort to a named function/functor: template<class T, class U> bool op_less(const typename NS1::NS2::C<T,U>::EntryType& lhs, const typename NS1::NS2::C<T,U>::EntryType& rhs) { std::cout<< "called" <<std::endl; return true; } .... template<typename T1, typename T2> void C<T1, T2>::FindX(xType x) const { std::cout<< "inside Find"<<std::endl; if ( op_less<T1,T2>(mContainer[0], mContainer[1]) ) { std::cout<<" 0 < 1 "<<std::endl; } if ( op_less<T1,T2>(mContainer[1], mContainer[0]) ) { std::cout<<" 1 < 0 "<<std::endl; } } V -- Please remove capital 'A's when replying by e-mail I do not respond to top-posted replies, please don't ask |
Re: operator< for algorithms
On Apr 2, 2:17 pm, "Hicham Mouline" <hic...@mouline.org> wrote:
> namespace NS1 { namespace NS2 { > template <typename T1, typename T2> > class C { > public: > typedef T1::xType xType; > typedef T1::yType yType; You are, presumably, using an older compiler. The above shouldn't compile (and won't with most newer compilers); you need an additional typename. > ... > private: > typedef std::pair< xType, yType> EntryType; > boost::array< EntryType , size > ContainerType; > .... > }; > ... > }} > I need to use std::lower_bound and sorting algorithms on my > ContainerType. That could be tricky if either xType or yType don't support comparison. And if they both support <, then your EntryType already has an operator<, which you don't want to change (since that would confuse any reader). And if EntryType supports <, then boost::array should as well. (I've not verified the latter, but as far as I know, boost::array adheres to the requirements of a container in the standard.) > Where (which namespace) and how can I define the operator< > comparing 2 EntryType for the std:: algorithms to use that > operator? > Note I use these std::algorithms only in member functions of > the C template. So I wish to define the operator< in a way > that is specific and visible only to C template. That's a tricky one. The correct answer is: in the namespace where one of the actual types was defined, i.e. where the T1 of the instantiation was defined. Except that, as mentionned, you can't define an operator< for EntryType or ContainerType, since the standard already defines one. If the standard operator isn't appropriate, then There are two simple solutions: -- Drop std::pair. Using it is probably an error anyway---do the two components really have a semantic of "first" and "second"? (There are cases where they do, but in those cases, the standard operator is appropriate.) Just define a nested class (or simply a struct) with the two types, and the operator< defined as you want. -- Don't use <. All of the functions involving order (sort, lower_bound, etc.) have a overload taking an additional argument specifying the ordering function. So you provide a nested class (fuctional object) which defines the ordering you want, and pass an instance of it to the function each time. -- James Kanze (GABI Software) email:james.kanze@gmail.com Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 place Sémard, 78210 St.-Cyr-l'École, France, +33 (0)1 30 23 00 34 |
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