C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  user-defined predicate function inside class          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Pavel Guest Posted: Thu Jun 26, 2003 10:28 pm    Post subject: user-defined predicate function inside class I have problem to desing the user-defined predicate function arch_Compare for Std C++ sort algorithm inside the class <Parch>. The only way I found was declare this function as friend, but then m_nSortKey have to be static. /*friend bool arch_Compare( PArchElem elem1, PArchElem elem2 ); static int m_nSortKey;*/ Is there another solution where m_nSortKey don´t have to be static? Thanks. /* source code which is not correct for Visual C++*/ class PArchElem{ private: char szName[41]; char szAddress[41]; public: PArchElem(){}; ~PZakArchiv(){}; char* getName(){return m_szName;}; char* getAddress(){return m_szAddress;}; }; class PArch{ private: deque<PArchElem> m_dqArch; int m_nSortKey; public: PArch(); ~PArch(); bool PArch::arch_sort(); bool arch_Compare (PArchElem elem1, PArchElem elem2); }; bool PArch::arch_sort(){ sort(m_dqArch.begin(),m_dqZakArch.end(),arch_Compare); return true; } bool PArch::arch_Compare( PArchElem elem1, PArchElem elem2 ){ double dResult; switch(m_nSortKey){ case NAME: dResult=lstrcmpi(elem1.getName(),elem2.getName()); break; case ADDRESS: dResult=lstrcmpi(elem1.getAddress(),elem2.getAddress()); break; default: dResult=0; break; } return dResult>0; } [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Daniel Spangenberg Guest Posted: Fri Jun 27, 2003 6:02 pm    Post subject: Re: user-defined predicate function inside class Hello Pavel! Pavel schrieb: Quote: I have problem to desing the user-defined predicate function arch_Compare for Std C++ sort algorithm inside the class <Parch>. The only way I found was declare this function as friend, but then m_nSortKey have to be static. /*friend bool arch_Compare( PArchElem elem1, PArchElem elem2 ); static int m_nSortKey;*/ Is there another solution where m_nSortKey don´t have to be static? Thanks. In general, a much more flexible and encapsulated ansatz is the usage of functors instead of functions. This has the additional advantage, that the comparator could simply contain the sortkey itself. Additionally I would recommend, that the arguments of your comparator should better be const PArchElem& instead of PArchElem. Quote: /* source code which is not correct for Visual C++*/ class PArchElem{ private: char szName[41]; char szAddress[41]; public: PArchElem(){}; ~PZakArchiv(){}; char* getName(){return m_szName;}; // Provide const-overload for this: const char* getName() const {return m_szName;}; Quote: char* getAddress(){return m_szAddress;}; // Provide const-overload for this: const char* getAddress() const {return m_szAddress;}; Quote: }; class PArch{ private: deque<PArchElem> m_dqArch; int m_nSortKey; public: PArch(); ~PArch(); bool PArch::arch_sort(); // bool arch_Compare (PArchElem elem1, PArchElem elem2); struct ArchCompare; }; struct PArch::ArchCompare { explicit ArchCompare(int sortKey) : sortKey_(sortKey){} bool operator()(const PArchElem& elem1, const PArchElem& elem2) const { double dResult; // Why double and not int??? switch(sortKey_){ case NAME: dResult=lstrcmpi(elem1.getName(),elem2.getName()); break; case ADDRESS: dResult=lstrcmpi(elem1.getAddress(),elem2.getAddress()); break; default: dResult=0; break; } return dResult>0; } private: int sortKey_; }; bool PArch::arch_sort(){ sort(m_dqArch.begin(),m_dqZakArch.end(),ArchCompare(m_nSortKey)); return true; } Hope that helps, Daniel Spangenberg [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] 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 (Moderated) 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.