C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Problems with ....hmm, linker perhaps          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Patrick Kowalzick Guest Posted: Fri Oct 29, 2004 11:23 am    Post subject: Problems with ....hmm, linker perhaps Dear all, IMO the following program is legal and should compile. //***** code start ********* // Definition of class A template <typename T> struct A { typedef T value_type; }; // Definition of class B template <typename> struct B {}; // Function foo // returntype important ! template <typename T> B<typename T::value_type> foo() { return B<typename T::value_type>(); }; int main() { typedef B< int >( * ptr )(); // Function pointer ptr foo_ptr = foo< A; // Initialization of function pointer return 0; } //***** code end ********* It builds fine with g++ and MSVC7.1, but the latter one fails linking: unresolved external symbol "struct B<int> __cdecl foo<struct A(void)" (??$foo@U?$A@H@@@@YA?AU?$B@H@@XZ) referenced in function _main what I do not really understand. It is getting a lit more weird now. If I change ptr foo_ptr = foo< A; to ptr foo_ptr ; foo_ptr = foo< A; it compiles and links fine as well with MSVC 7.1. Before I blame anyone, I want to ask if I overlooked something? IMO the code is fine. Regards, Patrick Back to top JKop Guest Posted: Fri Oct 29, 2004 11:56 am    Post subject: Re: Problems with ....hmm, linker perhaps Quote: If I change ptr foo_ptr = foo< A; to ptr foo_ptr ; foo_ptr = foo< A; it compiles and links fine as well with MSVC 7.1. Well, without scrutanizing your code too much, the only difference in the above is that the former calls a constructor, while the latter calls the default constructor and then calls operator=. -JKop Back to top Thomas Maier-Komor Guest Posted: Fri Oct 29, 2004 11:57 am    Post subject: Re: Problems with ....hmm, linker perhaps Patrick Kowalzick wrote: Quote: Dear all, IMO the following program is legal and should compile. //***** code start ********* // Definition of class A template <typename T> struct A { typedef T value_type; }; // Definition of class B template <typename> struct B {}; // Function foo // returntype important ! template <typename T B { return B<typename T::value_type>(); }; int main() { typedef B< int >( * ptr )(); // Function pointer ptr foo_ptr = foo< A; // Initialization of function pointer return 0; } //***** code end ********* It builds fine with g++ and MSVC7.1, but the latter one fails linking: unresolved external symbol "struct B<int> __cdecl foo<struct A(void)" (??$foo@U?$A@H@@@@YA?AU?$B@H@@XZ) referenced in function _main what I do not really understand. It is getting a lit more weird now. If I change ptr foo_ptr = foo< A; to ptr foo_ptr ; foo_ptr = foo< A; it compiles and links fine as well with MSVC 7.1. Before I blame anyone, I want to ask if I overlooked something? IMO the code is fine. Regards, Patrick compiles and links fine with Sun Studio 9... Back to top Patrick Kowalzick Guest Posted: Fri Oct 29, 2004 12:02 pm    Post subject: Re: Problems with ....hmm, linker perhaps Quote: compiles and links fine with Sun Studio 9... Thx. Back to top Unforgiven Guest Posted: Fri Oct 29, 2004 12:06 pm    Post subject: Re: Problems with ....hmm, linker perhaps "Patrick Kowalzick" <Patrick.Kowalzick (AT) cern (DOT) ch> wrote Quote: Dear all, IMO the following program is legal and should compile. I concur with your opinion. I tested and verified that VC7.1 does not. I think it's not a problem with the linker though, it looks as if the compiler isn't instantiating the foo<A template, so when the linker looks for it, it finds nothing. I also tested this under Visual C++ 2005 (VC8) beta 1 ([url]http://lab.msdn.microsoft.com/vs2005/)[/url], and it compiles and links fine, which seems to suggest this is indeed a bug in VC7.1 which has been fixed for VC8. -- Unforgiven Back to top Patrick Kowalzick Guest Posted: Fri Oct 29, 2004 12:08 pm    Post subject: Re: Problems with ....hmm, linker perhaps Hi JKop, Quote: If I change ptr foo_ptr = foo< A; to ptr foo_ptr ; foo_ptr = foo< A; it compiles and links fine as well with MSVC 7.1. Well, without scrutanizing your code too much, the only difference in the above is that the former calls a constructor, while the latter calls the default constructor and then calls operator=. [answer for JKop] Bullshit. [answer for the rest] I doubt that for function pointers constructors must be called. Is this compiler dependent? Whats the terminology for built-in types? Reagrds, Patrick Back to top Patrick Kowalzick Guest Posted: Fri Oct 29, 2004 12:11 pm    Post subject: Re: Problems with ....hmm, linker perhaps Dear Unforgiven, Quote: IMO the following program is legal and should compile. I concur with your opinion. I tested and verified that VC7.1 does not. I think it's not a problem with the linker though, it looks as if the compiler isn't instantiating the foo<A template, so when the linker looks for it, it finds nothing. I also tested this under Visual C++ 2005 (VC8) beta 1 ([url]http://lab.msdn.microsoft.com/vs2005/)[/url], and it compiles and links fine, which seems to suggest this is indeed a bug in VC7.1 which has been fixed for VC8. Thanks a lot. So it seems that I have to search a workaround for my application , which has a little bit different structure compared to the testcase. Patrick Back to top JKop Guest Posted: Fri Oct 29, 2004 12:19 pm    Post subject: Re: Problems with ....hmm, linker perhaps Quote: [answer for JKop] Bullshit. Perhaps I should be more general: A) AnyClass blah = some_expression; This calls a contructor, supplying "some_expression" as an argument. B) AnyClass blah; blah = some_expression; This calls the default constructor. It then calls operator=. Use your own intelligence to see what I'm getting at. -JKop Back to top Patrick Kowalzick Guest Posted: Fri Oct 29, 2004 12:29 pm    Post subject: Re: Problems with ....hmm, linker perhaps Quote: [answer for JKop] Bullshit. Yep. Quote: Perhaps I should be more general: A) AnyClass blah = some_expression; This calls a contructor, supplying "some_expression" as an argument. B) AnyClass blah; blah = some_expression; This calls the default constructor. It then calls operator=. You are talking about classes, don't you? See the OP, I was talking about function pointers. Regards, Patrick Back to top Richard Herring Guest Posted: Fri Oct 29, 2004 12:38 pm    Post subject: Re: Problems with ....hmm, linker perhaps In message <5zqgd.40415$Z14.14642 (AT) news (DOT) indigo.ie>, JKop <NULL (AT) NULL (DOT) NULL> writes Quote: [answer for JKop] Bullshit. Perhaps I should be more general: A) AnyClass blah = some_expression; This calls a contructor, supplying "some_expression" as an argument. B) AnyClass blah; blah = some_expression; This calls the default constructor. It then calls operator=. Use your own intelligence to see what I'm getting at. What is the type of foo_ptr? -- Richard Herring Back to top Rob Williscroft Guest Posted: Fri Oct 29, 2004 12:56 pm    Post subject: Re: Problems with ....hmm, linker perhaps Patrick Kowalzick wrote in news:clt96o$icc$1 (AT) sunnews (DOT) cern.ch in comp.lang.c++: Quote: int main() { typedef B< int >( * ptr )(); // Function pointer ptr foo_ptr = foo< A; // Initialization of function pointer return 0; } //***** code end ********* It builds fine with g++ and MSVC7.1, but the latter one fails linking: unresolved external symbol "struct B<int> __cdecl foo<struct A (void)" (??$foo@U?$A@H@@@@YA?AU?$B@H@@XZ) referenced in function _main This is a bug in MSVC 7.1, Its "forgoten" to do the implicit instantiation of foo< A< int > >. I haven't seen it in precisly this context (taking a function pointer) but in a few other's I have. As a minor data point I compiled with: cl -nologo -Za -Zc:forScope,wchar_t -EHsc -O1 -ML -Tptest.cpp and msvc *didn't* exhibit the problem, but if I compiled: cl test.cpp I got the unresolved external, I don't know which combination of option's achived this turnaround or why. Rob. -- http://www.victim-prime.dsl.pipex.com/ Back to top Andrey Tarasevich Guest Posted: Fri Oct 29, 2004 5:07 pm    Post subject: Re: Problems with ....hmm, linker perhaps Patrick Kowalzick wrote: Quote: ... int main() { typedef B< int >( * ptr )(); // Function pointer ptr foo_ptr = foo< A; // Initialization of function pointer return 0; } //***** code end ********* It builds fine with g++ and MSVC7.1, but the latter one fails linking: unresolved external symbol "struct B<int> __cdecl foo<struct A(void)" (??$foo@U?$A@H@@@@YA?AU?$B@H@@XZ) referenced in function _main ... Seems to be a compiler problem. Try using the address-of operator explicitly ptr foo_ptr = &foo< A; I remember that sometimes it helped to solve similar problems in MSVC++ 6, but I don't know whether it will help in MSVC++ 7. Explicit instantiation will probably also solve the problem, but that would be a high-maintenance solution. -- Best regards, Andrey Tarasevich Back to top Ron Natalie Guest Posted: Fri Oct 29, 2004 7:28 pm    Post subject: Re: Problems with ....hmm, linker perhaps There is a known bug in visual studio 6 when defining function templates that don't have the templated variables in their signature. Back to top Patrick Kowalzick Guest Posted: Mon Nov 01, 2004 8:45 am    Post subject: Re: Problems with ....hmm, linker perhaps Hi Andrey, Quote: Seems to be a compiler problem. Try using the address-of operator explicitly ptr foo_ptr = &foo< A; same problem,... Quote: I remember that sometimes it helped to solve similar problems in MSVC++ 6, but I don't know whether it will help in MSVC++ 7. Explicit instantiation will probably also solve the problem, but that would be a high-maintenance solution. but while I get around it like this: ptr foo_ptr; foo_ptr = &foo< A; it is ok for now . I documented in my code as a bug. Shall be enough.... Thanks, Patrick 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.