C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Compiling error          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message sergiozin@gmail.com Guest Posted: Tue Sep 27, 2005 11:21 am    Post subject: Compiling error Hi, here goes a very simple code, to me looks like everything is right, but I see an error compiling with VC6..., does anyone has a clue for what's wrong? Thanks template<int *INT_POINTER> class ClassA { public: static void P(){} }; int a; int x[3]; int main() { /*OK*/ ClassA<&a>:(); /*error C2964: invalid expression as template parameter*/ ClassA<&x[0]>:(); return 0; } [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Gerhard Menzl Guest Posted: Tue Sep 27, 2005 3:36 pm    Post subject: Re: Compiling error [email]sergiozin (AT) gmail (DOT) com[/email] wrote: Quote: Hi, here goes a very simple code, to me looks like everything is right, but I see an error compiling with VC6..., does anyone has a clue for what's wrong? Thanks template<int *INT_POINTER class ClassA { public: static void P(){} }; int a; int x[3]; int main() { /*OK*/ ClassA<&a>:(); /*error C2964: invalid expression as template parameter*/ ClassA<&x[0]>:(); return 0; } Addresses of array elements are not valid template arguments according of 14.3.2 of the C++ Standard. -- Gerhard Menzl #dogma int main () Humans may reply by replacing the thermal post part of my e-mail address with "kapsch" and the top level domain part with "net". [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Daniel Krügler Guest Posted: Tue Sep 27, 2005 4:45 pm    Post subject: Re: Compiling error [email]sergiozin (AT) gmail (DOT) com[/email] wrote: Quote: Hi, here goes a very simple code, to me looks like everything is right, but I see an error compiling with VC6..., does anyone has a clue for what's wrong? Thanks template<int *INT_POINTER class ClassA { public: static void P(){} }; int a; int x[3]; int main() { /*OK*/ ClassA<&a>:(); /*error C2964: invalid expression as template parameter*/ ClassA<&x[0]>:(); return 0; } This is no problem with your compiler, but a language restriction, because ClassA<&x[0]>:() does not fulfill the requirements described in 14.3.2/p. 1. 14.3.2/p. 3 says: "[Note: Addresses of array elements and names or addresses of non-static class members are not acceptable template-arguments. [Example: template<int* p> class X { }; int a[10]; struct S { int m; static int s; } s; X<&a[2]> x3; // error: address of array element X<&s.m> x4; // error: address of non-static member X<&s.s> x5; // error: &S::s must be used X<&S::s> x6; // OK: address of static member —end example] —end note]" Greetings from Bremen, Daniel Krügler [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top André Kempe Guest Posted: Wed Sep 28, 2005 1:51 pm    Post subject: Re: Compiling error Daniel Krügler schrieb: <snip> Quote: template<int *INT_POINTER class ClassA { public: static void P(){} }; snip "[Note: Addresses of array elements and names or addresses of non-static class members are not acceptable template-arguments. [Example: template int a[10]; struct S { int m; static int s; } s; X<&a[2]> x3; // error: address of array element snip But how about passing the whole array as ClassA<a>? Is this allowed by the standard? [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Daniel Krügler Guest Posted: Wed Sep 28, 2005 2:48 pm    Post subject: Re: Compiling error André Kempe wrote: Quote: Daniel Krügler schrieb: snip template<int *INT_POINTER class ClassA { public: static void P(){} }; snip "[Note: Addresses of array elements and names or addresses of non-static class members are not acceptable template-arguments. [Example: template int a[10]; struct S { int m; static int s; } s; X<&a[2]> x3; // error: address of array element snip But how about passing the whole array as ClassA<a>? Is this allowed by the standard? The following is allowed: template<int (&p)[10]> class X { }; int a[10]; X<a> x3; This also: template<int* p> class X { }; int a[10]; X<a> x3; Greetings from Bremen, Daniel Krügler [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top André Kempe Guest Posted: Thu Sep 29, 2005 8:12 pm    Post subject: Re: Compiling error Daniel Krügler schrieb: <snip> Quote: The following is allowed: template<int (&p)[10]> class X { }; int a[10]; X<a> x3; This also: template<int* p> class X { }; int a[10]; X<a> x3; snip So one could bypass the "adress of array element is not allowed"-issue by giving the index as a seperate template parameter! so whats the point of the standard to prohibit this? Greetings from Dresden! André [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top kanze Guest Posted: Sat Oct 01, 2005 2:01 am    Post subject: Re: Compiling error André Kempe wrote: Quote: Daniel Krügler schrieb: snip The following is allowed: template<int (&p)[10]> class X { }; int a[10]; X<a> x3; This also: template<int* p> class X { }; int a[10]; X<a> x3; snip So one could bypass the "adress of array element is not allowed"-issue by giving the index as a seperate template parameter! so whats the point of the standard to prohibit this? You don't even have to do that: X<a+3> works. What is forbidden (if memory serves me correctly -- the machine on which I have my copy of the standard is down again) is the indexation operator itself. Something like: template < int i > class X {} ; int a[] = { 1, 2, 5, 10 } ; X< a[ 2 ] > anX ; is forbidden, for obvious reasons. Allowing &a[2] would require a special case. -- James Kanze GABI Software mailto:james.kanze (AT) free (DOT) fr 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 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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