C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  shared member between class instances          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message markww Guest Posted: Fri Aug 25, 2006 8:42 am    Post subject: shared member between class instances Hi, I want all instance of a class type to share one variable, I forgot how to do that: class CMyClass { public: static int m_nSharedRes; }; Now can all instances of CMyClass share that one variable, and see the changes reflected in each instance? Like: CMyClass a; CMyClass b; a.m_nSharedRes = 44; // Now b can see it as 44 too. cout << b.m_nSharedRes << endl; // should print 44; Thanks! Back to top Steve Pope Guest Posted: Fri Aug 25, 2006 8:42 am    Post subject: Re: shared member between class instances markww <markww (AT) gmail (DOT) com> wrote: Quote: Hi, I want all instance of a class type to share one variable, I forgot how to do that: class CMyClass { public: static int m_nSharedRes; }; Now can all instances of CMyClass share that one variable, and see the changes reflected in each instance? Like: CMyClass a; CMyClass b; a.m_nSharedRes = 44; // Now b can see it as 44 too. cout << b.m_nSharedRes << endl; // should print 44; Thanks! If you define it somewhere with int CMyClass::m_nSharedRes; it should work as you intended. Steve Back to top Steve Pope Guest Posted: Fri Aug 25, 2006 8:42 am    Post subject: Re: shared member between class instances markww <markww (AT) gmail (DOT) com> wrote: Quote: Steve Pope wrote: class CMyClass { public: static int m_nSharedRes; }; Quote: CMyClass a; CMyClass b; a.m_nSharedRes = 44; // Now b can see it as 44 too. cout << b.m_nSharedRes << endl; // should print 44; If you define it somewhere with int CMyClass::m_nSharedRes; it should work as you intended. So I just define it like: class CMyClass { public: int CMyClass::m_nSharedRes; }; ?? The definition: int CMyClass::m_nSharedRes; needs to be outside of the declaration of the class. You need to do this in addtion to the code in your first post. Remember that the a class declaration by itself allocates no storage. Steve Back to top markww Guest Posted: Fri Aug 25, 2006 8:51 am    Post subject: Re: shared member between class instances Steve Pope wrote: Quote: markww <markww (AT) gmail (DOT) com> wrote: Hi, I want all instance of a class type to share one variable, I forgot how to do that: class CMyClass { public: static int m_nSharedRes; }; Now can all instances of CMyClass share that one variable, and see the changes reflected in each instance? Like: CMyClass a; CMyClass b; a.m_nSharedRes = 44; // Now b can see it as 44 too. cout << b.m_nSharedRes << endl; // should print 44; Thanks! If you define it somewhere with int CMyClass::m_nSharedRes; it should work as you intended. Steve Hi Steve, So I just define it like: class CMyClass { public: int CMyClass::m_nSharedRes; }; ?? Thanks Back to top Greg Guest Posted: Fri Aug 25, 2006 9:00 am    Post subject: Re: shared member between class instances markww wrote: Quote: Steve Pope wrote: markww <markww (AT) gmail (DOT) com> wrote: Hi, I want all instance of a class type to share one variable, I forgot how to do that: class CMyClass { public: static int m_nSharedRes; }; Now can all instances of CMyClass share that one variable, and see the changes reflected in each instance? Like: CMyClass a; CMyClass b; a.m_nSharedRes = 44; // Now b can see it as 44 too. cout << b.m_nSharedRes << endl; // should print 44; Thanks! If you define it somewhere with int CMyClass::m_nSharedRes; it should work as you intended. Steve Hi Steve, So I just define it like: class CMyClass { public: int CMyClass::m_nSharedRes; }; ?? No, m_nSharedRes must be declared static in order for each CMyClass object to share the same variable. Greg Back to top markww Guest Posted: Fri Aug 25, 2006 9:05 am    Post subject: Re: shared member between class instances Steve Pope wrote: Quote: markww <markww (AT) gmail (DOT) com> wrote: Steve Pope wrote: class CMyClass { public: static int m_nSharedRes; }; CMyClass a; CMyClass b; a.m_nSharedRes = 44; // Now b can see it as 44 too. cout << b.m_nSharedRes << endl; // should print 44; If you define it somewhere with int CMyClass::m_nSharedRes; it should work as you intended. So I just define it like: class CMyClass { public: int CMyClass::m_nSharedRes; }; ?? The definition: int CMyClass::m_nSharedRes; needs to be outside of the declaration of the class. You need to do this in addtion to the code in your first post. Remember that the a class declaration by itself allocates no storage. Steve Ah yeah now I remember. 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