C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  template function called in template class          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Dominique Marcadet Guest Posted: Sun Feb 29, 2004 4:01 am    Post subject: template function called in template class Given the following code : struct A { template < typename T > T a() { return T(0); } }; template < typename Z > struct B { void b() { A a0; void (A::*f)() = &A::a<int>; // 1a int i = a0.*f(); // 1b int j = a0.a<int>(); // 2 } }; g++ (tested with gcc 3.3 on Mac OS X 10.3.2 and gcc 3.3.3) gives me a : parse error before `;' token on line //2 (but it is OK on lines //1a and //1b) IMHO, it's a bug of gcc, but before submitting it to the g++ team, I would like to know if I am not wrong in my analysis. NB: if B is not a template class, errors occured first at line //1a and I am unable to find any reason. Thank you in advance for your help, Dominique [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Dominique Marcadet Guest Posted: Sun Feb 29, 2004 4:46 pm    Post subject: Re: template function called in template class I respond to myself after having found the answer (I should have search a bit further in the group). Quote: struct A { template < typename T T a() { return T(0); } }; template < typename Z struct B { void b() { A a0; void (A::*f)() = &A::a int i = a0.*f(); // 1b int j = a0.a<int>(); // 2 To avoid ambiguity, you have to tell the compiler that a is a template : int j = a0.template a<int>(); // 2 (found in the thread "compile problem with template (gcc-2.95.x,gcc 3.0, Comeau)") Quote: } }; NB: if B is not a template class, errors occured first at line //1a and I am unable to find any reason. After correcting line // 1a: int (A::*f)() = &A::a<int>; // 1a the line 1b should be written as : int i = (a0.*f)(); // 1b (found answer in thread "another pointer to member function question"). Dominique [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Stephen C. Dewhurst Guest Posted: Sun Feb 29, 2004 4:54 pm    Post subject: Re: template function called in template class On 28 Feb 2004 23:01:48 -0500, [email]Dominique.Marcadet (AT) supelec (DOT) fr[/email] (Dominique Marcadet) wrote: Quote: IMHO, it's a bug of gcc, but before submitting it to the g++ team, I would like to know if I am not wrong in my analysis. I think gcc is right on this: template < typename Z > struct B { void b() { A a0; int (A::*f)() = &A::a<int>; // return type was void // should be int int i = (a0.*f)(); // missing parens int j = (a0.a<int>)(); // missing parens } }; Steve Steve Dewhurst www.semantics.org [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Carl Barron Guest Posted: Sun Feb 29, 2004 5:40 pm    Post subject: Re: template function called in template class Dominique Marcadet <Dominique.Marcadet (AT) supelec (DOT) fr> wrote: Quote: Given the following code : struct A { template < typename T T a() { return T(0); } }; template < typename Z struct B { void b() { A a0; void (A::*f)() = &A::a int i = a0.*f(); // 1b int j = a0.a<int>(); // 2 } }; g++ (tested with gcc 3.3 on Mac OS X 10.3.2 and gcc 3.3.3) gives me a : parse error before `;' token on line //2 (but it is OK on lines //1a and //1b) IMHO, it's a bug of gcc, but before submitting it to the g++ team, I would like to know if I am not wrong in my analysis. NB: if B is not a template class, errors occured first at line //1a and I am unable to find any reason. Thank you in advance for your help, Dominique using CW 5.3 on this old macos 8.6 machine [cw 9.x is on my 'office panter machine] it says that 1a is a 'unimpliemented feature, could be gcc is lost in space?? Will test this during week on mwc92 but I think it might have a problem. if I did this cw 5.3 reported no problem. I am assuming that this is not the solution desired. but it may solve the problem for the given code. template <class T> struct A { T a() { return T(0); } }; template < typename Z > struct B { void b() { A<int> a0; int (A<int>::*f)() = &A<int>::a; // 1a int i = (a0.*f)(); // 1b int j = a0.a(); // 2 } }; struct C { B<int> bar; void foo(){bar.b();} }; [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Gabriel Dos Reis Guest Posted: Sun Feb 29, 2004 5:44 pm    Post subject: Re: template function called in template class [email]Dominique.Marcadet (AT) supelec (DOT) fr[/email] (Dominique Marcadet) writes: Quote: Given the following code : struct A { template < typename T T a() { return T(0); } }; template < typename Z struct B { void b() { A a0; void (A::*f)() = &A::a int i = a0.*f(); // 1b int j = a0.a<int>(); // 2 } }; g++ (tested with gcc 3.3 on Mac OS X 10.3.2 and gcc 3.3.3) gives me a : parse error before `;' token on line //2 (but it is OK on lines //1a and //1b) IMHO, it's a bug of gcc, but before submitting it to the g++ team, I would like to know if I am not wrong in my analysis. It is a known bug in the parser of any version of GCC prior to 3.4.0 (not yet released, but is upcoming). A workaround is to rewrite line // 2 as: int j = a0.a::template<int>(); The infamous "::template" is not required, but it is allowed in that context. -- Gabriel Dos Reis [email]gdr (AT) cs (DOT) tamu.edu[/email] Texas A&M University -- Computer Science Department 301, Bright Building -- College Station, TX 77843-3112 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Stephen C. Dewhurst Guest Posted: Sun Feb 29, 2004 11:57 pm    Post subject: Re: template function called in template class On 29 Feb 2004 11:46:10 -0500, [email]Dominique.Marcadet (AT) supelec (DOT) fr[/email] (Dominique Marcadet) wrote: Quote: struct A { template < typename T T a() { return T(0); } }; template < typename Z struct B { void b() { A a0; void (A::*f)() = &A::a int i = a0.*f(); // 1b int j = a0.a<int>(); // 2 To avoid ambiguity, you have to tell the compiler that a is a template : int j = a0.template a<int>(); // 2 Actually, that's not the particular problem here, since the compiler is able to determine that A::a is a template by inspection. However, it would be a problem, and the "template" keyword required if A were itself a template, and the A template was being used in a context where its instantiation arguments were not known precisely: template <typename X> struct A { template < typename T > T a() { return T(0); } }; template < typename Y, typename Z > struct B { void b() { A<Y> a0; //... Z j = a0.template a<Z>(); // now we need "template" //... Steve Steve Dewhurst www.semantics.org [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Rob Williscroft Guest Posted: Mon Mar 01, 2004 12:04 am    Post subject: Re: template function called in template class Gabriel Dos Reis wrote in news:m33c8uxkx6.fsf (AT) merlin (DOT) cs.tamu.edu: Quote: Dominique.Marcadet (AT) supelec (DOT) fr (Dominique Marcadet) write | int j = a0.a<int>(); // 2 It is a known bug in the parser of any version of GCC prior to 3.4.0 (not yet released, but is upcoming). A workaround is to rewrite line // 2 as: int j = a0.a::template<int>(); A typo I think: int j = a0.template a< int >(); Quote: The infamous "::template" is not required, but it is allowed in that context. Rob. -- http://www.victim-prime.dsl.pipex.com/ [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Gabriel Dos Reis Guest Posted: Mon Mar 01, 2004 12:25 pm    Post subject: Re: template function called in template class Rob Williscroft <rtw (AT) freenet (DOT) REMOVE.co.uk> writes: Quote: Gabriel Dos Reis wrote in news:m33c8uxkx6.fsf (AT) merlin (DOT) cs.tamu.edu: [email]Dominique.Marcadet (AT) supelec (DOT) fr[/email] (Dominique Marcadet) write | int j = a0.a<int>(); // 2 It is a known bug in the parser of any version of GCC prior to 3.4.0 (not yet released, but is upcoming). A workaround is to rewrite line // 2 as: int j = a0.a::template<int>(); A typo I think: int j = a0.template a< int >(); Sigh. You're absolutely correct. I should not have been posting when it was obvsiously time to go to bed. -- Gabriel Dos Reis [email]gdr (AT) cs (DOT) tamu.edu[/email] Texas A&M University -- Computer Science Department 301, Bright Building -- College Station, TX 77843-3112 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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