C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  function overloading with default argument          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message praveen Guest Posted: Sat Jan 15, 2005 10:26 am    Post subject: function overloading with default argument I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Francis Glassborow Guest Posted: Sun Jan 16, 2005 4:13 am    Post subject: Re: function overloading with default argument In article <1105774712.050668.268380 (AT) z14g2000cwz (DOT) googlegroups.com>, praveen <praveen.varrier (AT) gmail (DOT) com> writes Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); I am assuming that was a typo and you meant: fun1(int a, int b = 2); In addition neither of the above declarations would be accepted by a conforming compiler because they lack a return type. Quote: When i call it this way, fun1(3); which overloaded fun1(..) will be called Neither. The compiler will issue an ambiguity error. It will not be possible to call your first version in any context where the second one is visible. As a matter of good design, overloaded functions should 'do the same thing'. Given that, replace your overload set with: int fun1(int, int); inline int fun1(int a){ return fun1(a, 2); } -- Francis Glassborow ACCU Author of 'You Can Do It!' see http://www.spellen.org/youcandoit For project ideas and contributions: http://www.spellen.org/youcandoit/projects [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top carletoncourses@yahoo.ca Guest Posted: Sun Jan 16, 2005 4:28 am    Post subject: Re: function overloading with default argument Hello Praveen: The compiler should generate an error in this case. Say I have the program class A { public: void f1( int a ) { } void f1( int a, int b = 2) { } }; int main(int argc, char * argv[] ) { A a; a.f1(3); return 0; } If I try to compile it using VC++ 6.0, I would get an error like this: error C2668: 'f1' : ambiguous call to overloaded function Bill praveen wrote: Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Abhishek Pandey Guest Posted: Sun Jan 16, 2005 4:39 am    Post subject: Re: function overloading with default argument "praveen" <praveen.varrier (AT) gmail (DOT) com> wrote Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called None. Have you tried to run this code yourself. The call is very clearly ambiguous [If I assume you meant "int a" in the second declaration instead of "in a" ] Read Scott Meyers' Effective C++ : Item 24, Choose carefully between function overloading and parameter defaulting to understand when to use default argument and when to use function overloading. Thanks Abhishek Quote: [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Sumit Rajan Guest Posted: Sun Jan 16, 2005 4:40 am    Post subject: Re: function overloading with default argument praveen wrote: Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called Compile-time error. -- Sumit Rajan <sumit.rajan (AT) gmail (DOT) com> [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top carletoncourses@yahoo.ca Guest Posted: Sun Jan 16, 2005 4:46 am    Post subject: Re: function overloading with default argument Hello: Compiler would treat the calls to such function as ambiguous. Lets see an example program to explain: class A { public: void fun1( int a ) { } void fun1( int a, int b = 2) { } }; int main(int argc, char * argv[] ) { A a; a.fun1(3); return 0; } If I try compiling it using Visual C++ 6.0, I get this error: error C2668: 'fun1' : ambiguous call to overloaded function Hope that answers your question. Bill praveen wrote: Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top René Kjellerup Guest Posted: Sun Jan 16, 2005 4:55 am    Post subject: Re: function overloading with default argument it will never compile as the declaration is ambiguous so the answer would be none of them. René praveen wrote: Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.0.300 / Virus Database: 265.6.12 - Release Date: 14-01-2005 [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jesper Schmidt Guest Posted: Sun Jan 16, 2005 4:57 am    Post subject: Re: function overloading with default argument The code shouldn't compile because both overloads match the call equally well (ambiguous call to overloaded function). -Jesper "praveen" <praveen.varrier (AT) gmail (DOT) com> wrote Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top James Kanze Guest Posted: Sun Jan 16, 2005 5:00 am    Post subject: Re: function overloading with default argument praveen wrote: Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); Which is, I believe, illegal. Quote: When i call it this way, fun1(3); which overloaded fun1(..) will be called Neither. The call is ambiguous, and the code won't compile. For overloading purposes, a function with a default parameter is considered as if it were two functions. -- James Kanze home: www.gabi-soft.fr Conseils en informatique orientée objet/ Beratung in objektorientierter Datenverarbeitung 9 pl. Pierre 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. First time posters: Do this! ] Back to top Victor Bazarov Guest Posted: Sun Jan 16, 2005 5:04 am    Post subject: Re: function overloading with default argument "praveen" <praveen.varrier (AT) gmail (DOT) com> wrote... Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called Ambiguous. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Fah!m Guest Posted: Sun Jan 16, 2005 5:23 am    Post subject: Re: function overloading with default argument I think that depending on the compiler u r using...u shud get an error as there is ambiguity in the above case...compiler shud complain... [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Jeffrey Baker Guest Posted: Sun Jan 16, 2005 5:23 am    Post subject: Re: function overloading with default argument "praveen" <praveen.varrier (AT) gmail (DOT) com> wrote Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called You will get an error message :fun1: ambiguous call to overloaded function The default argument won't allow an overload. The two argument needs only one argument, but the compiler sees two, so it won't accept it. jb Quote: [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top L.Suresh Guest Posted: Sun Jan 16, 2005 5:25 am    Post subject: Re: function overloading with default argument There are two candidate functions. The call is ambiguous. --lsu [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Maciej Sobczak Guest Posted: Sun Jan 16, 2005 5:29 am    Post subject: Re: function overloading with default argument praveen wrote: Quote: I am in a big dilema now the problem is,I have an overloaded function, 1) fun1(int a); 2) fun1(in a,int b=2); When i call it this way, fun1(3); which overloaded fun1(..) will be called This call is ambiguous. For the purpose of overloading resolution, the parameters of candidate functions with additional default values are "truncated". Above, there are two candidate functions. First is: fun1(int a) // 1. the other is: fun1(int a, int b = 2) // 2. but the additional default parameter is truncated, giving: fun1(int a) // 2. Since, after truncation, 1. and 2. are the same (precisely: none is better than the other), the call is ambiguous. See 13.1/3 and 13.3.2/2 for details. -- Maciej Sobczak : http://www.msobczak.com/ Programming : http://www.msobczak.com/prog/ [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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