VS 2005 compiler died on this recursive template
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From: Alex on 15 Mar 2010 13:25 { edits: 22 excess spaces in the commented code line removed. The question of this article is in the subject line "VS 2005 compiler died on this recursive template". -mod } template <int i> struct Factorial { enum { N = i<=0? 1 : i*Factorial<i-1>::N }; }; //template<> struct Factorial<0> { enum { N = 1 }; }; // IF uncoment � working fine void main() { int factorial=Factorial<3>::N; } -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Daniel Krügler on 15 Mar 2010 19:44 On 16 Mrz., 05:25, Alex <alexey.d.zait...(a)gmail.com> wrote: > template <int i> > struct Factorial > { > enum { N = i<=0? 1 : i*Factorial<i-1>::N };}; > > //template<> struct Factorial<0> { enum { N = 1 }; }; > // IF uncoment � working fine > void main() { > int factorial=Factorial<3>::N; > } 1) The main function must have an int return type. 2) The specialization is required. It doesn't help that you check "i <= 0" inside the primary template to prevent the compiler from instantiating Factorial<i-1> because the kind of expression it occurs in, naming a member via qualification ("Factorial<i-1>::N"), does require an instantiation of the class Factorial<i-1> even though the branch will not be entered. But *if* it instantiates Factorial<i-1>, this is a never- ending story without any explicit specialization. HTH & Greetings from Bremen, - Daniel -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ]
From: Bart van Ingen Schenau on 15 Mar 2010 19:46
On Mar 16, 5:25 am, Alex <alexey.d.zait...(a)gmail.com> wrote: > { edits: 22 excess spaces in the commented code line removed. > > The question of this article is in the subject line > "VS 2005 compiler died on this recursive template". > -mod } > > template <int i> > struct Factorial > { > enum { N = i<=0? 1 : i*Factorial<i-1>::N };}; The test in the ?:-operator does not break the recursive instantiation of the template, because the rightmost argument still has to be instantiated (even if i is 0 or less) to have a valid expression. Only after it is verified that the expression is valid can the test come into play, but that is already too late. > > //template<> struct Factorial<0> { enum { N = 1 }; }; > // IF uncoment � working fine > void main() { > int factorial=Factorial<3>::N; > > } > Bart v Ingen Schenau -- [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] |