C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  static member function          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message MJ Guest Posted: Fri Apr 29, 2005 2:04 pm    Post subject: static member function Hi I have a basic doubt about structure. I have a class in which a I have declared a static funtion class A { public: static a; static f(); }; Can I access the the static function without creating a instance of a class A. Can I access the static variable without creating a instance of a class A. MJ Back to top Alvin Guest Posted: Fri Apr 29, 2005 2:13 pm    Post subject: Re: static member function MJ wrote: Quote: Hi I have a basic doubt about structure. I have a class in which a I have declared a static funtion class A { public: static a; static f(); }; Can I access the the static function without creating a instance of a class A. Can I access the static variable without creating a instance of a class A. MJ http://cplus.about.com/od/beginnerctutorial/l/aa080802a.htm -- Alvin Back to top Victor Bazarov Guest Posted: Fri Apr 29, 2005 2:14 pm    Post subject: Re: static member function MJ wrote: Quote: I have a basic doubt about structure. I have a class in which a I have declared a static funtion class A { public: static a; static <what type?> a; ??? Quote: static f(); static <what return value type?> f(); ??? Quote: }; Can I access the the static function without creating a instance of a class A. Yes. Quote: Can I access the static variable without creating a instance of a class A. Yes. V Back to top abecedarian@spambob.com Guest Posted: Fri Apr 29, 2005 2:17 pm    Post subject: Re: static member function MJ wrote: Quote: Hi I have a basic doubt about structure. I have a class in which a I have declared a static funtion class A { public: static int a; static float f() { return 3.14; } Quote: }; // in *.cpp int A::a = -1; Quote: Can I access the the static function without creating a instance of a class A. float g = A::f(); Quote: Can I access the static variable without creating a instance of a class A. int b = A::a; Abe Back to top MJ Guest Posted: Fri Apr 29, 2005 2:53 pm    Post subject: Re: static member function Hi I tried the following code -------------------------------------------------------------- class A { public: static int a; static float f() { return 3.14;} }; int main () { //int A::a = -1; // line 1 float g = A::f(); // line 2 cout << g << endl; cin >> g; return 0 ; } -------------------------------------------------------------- if i uncommet the line 1 its giving me an error " definition or redeclaration illegal in current scope" but the static function I am able to access properly and there is no problem if I put both the lines out side the main loop it does not give me any error So does it mean that the static function are accessible but static variable are specific to scope ?? MJ Back to top Victor Bazarov Guest Posted: Fri Apr 29, 2005 2:58 pm    Post subject: Re: static member function MJ wrote: Quote: I tried the following code -------------------------------------------------------------- class A { public: static int a; static float f() { return 3.14;} }; int main () { //int A::a = -1; // line 1 float g = A::f(); // line 2 cout << g << endl; cin >> g; return 0 ; } -------------------------------------------------------------- if i uncommet the line 1 its giving me an error " definition or redeclaration illegal in current scope" but the static function I am able to access properly and there is no problem if I put both the lines out side the main loop it does not give me any error So does it mean that the static function are accessible but static variable are specific to scope ?? No. It means you're not defining the static data member where _required_. What does your C++ book say about defining static data members? What C++ book are you reading? V Back to top Alvin Guest Posted: Fri Apr 29, 2005 3:04 pm    Post subject: Re: static member function MJ wrote: Quote: Hi I tried the following code -------------------------------------------------------------- class A { public: static int a; static float f() { return 3.14;} }; int main () { //int A::a = -1; // line 1 float g = A::f(); // line 2 cout << g << endl; cin >> g; return 0 ; } -------------------------------------------------------------- if i uncommet the line 1 its giving me an error " definition or redeclaration illegal in current scope" but the static function I am able to access properly and there is no problem if I put both the lines out side the main loop it does not give me any error So does it mean that the static function are accessible but static variable are specific to scope ?? MJ Just remove the *int* from the line 1. In main() all you want to do is alter the static variable not re-declare it. So it would be: int main() { A::a = -1; ... } Also, there is another bug. A::a is undefined. You say what the *initial value* of A::a because check it as in: int main() { if(A::a > 10) cout << "A::a is greater than 10" << endl; ... } With your current implementation, the above code will have undefined behaviour (that just means it will act weird). -- Alvin Back to top MJ Guest Posted: Fri Apr 29, 2005 3:11 pm    Post subject: Re: static member function Hi I am reading scott mayor and thinking in C++ vol i and II Sorry I could not get what you mean ... I have declared the static data member in the class itself.. and I can do like that .. whats wrong in that .... See the code below it works fine when I am accessing the static variable outside ------------------------------------------------------------- class A { private: public: static int a; static float f() { return 3.14;} }; int A::a = -1; int main () { // A::a = -1; float g = A::f(); cout << g << endl; cin >> g; return 0 ; } ------------------------------------------------------------- MJ Back to top Rolf Magnus Guest Posted: Fri Apr 29, 2005 3:12 pm    Post subject: Re: static member function MJ wrote: Quote: Hi I tried the following code -------------------------------------------------------------- class A { public: static int a; static float f() { return 3.14;} }; int main () { //int A::a = -1; // line 1 float g = A::f(); // line 2 cout << g << endl; cin >> g; return 0 ; } -------------------------------------------------------------- if i uncommet the line 1 its giving me an error " definition or redeclaration illegal in current scope" And that's right. line 1 tries to define A::a, which isn't allowed within a function. You have to define A::a, but outside of a function. Quote: but the static function I am able to access properly and there is no problem if I put both the lines out side the main loop it does not give me any error. So does it mean that the static function are accessible but static variable are specific to scope ?? Nope. It means your syntax is wrong. Try: #include <iostream> class A { public: static int a; static float f() { return 3.14;} }; int A::a; int main () { using namespace std; A::a = -1; // line 1 float g = A::f(); // line 2 cout << g << endl; cin >> g; return 0 ; } Back to top Victor Bazarov Guest Posted: Fri Apr 29, 2005 3:14 pm    Post subject: Re: static member function Alvin wrote: Quote: MJ wrote: Hi I tried the following code -------------------------------------------------------------- class A { public: static int a; static float f() { return 3.14;} }; int main () { //int A::a = -1; // line 1 float g = A::f(); // line 2 cout << g << endl; cin >> g; return 0 ; } -------------------------------------------------------------- if i uncommet the line 1 its giving me an error " definition or redeclaration illegal in current scope" but the static function I am able to access properly and there is no problem if I put both the lines out side the main loop it does not give me any error So does it mean that the static function are accessible but static variable are specific to scope ?? MJ Just remove the *int* from the line 1. In main() all you want to do is alter the static variable not re-declare it. So it would be: int main() { A::a = -1; ... } Also, there is another bug. A::a is undefined. It's not a bug. The code won't link if A::a is undefined. Quote: [...] Back to top Victor Bazarov Guest Posted: Fri Apr 29, 2005 3:18 pm    Post subject: Re: static member function MJ wrote: Quote: I am reading scott mayor and thinking in C++ vol i and II Sorry I could not get what you mean ... I have declared the static data member in the class itself.. and I can do like that .. whats wrong in that .... Absolutely nothing. You did the right thing. And you actually used the right term describing what you did: *declared* the static data. Quote: See the code below it works fine when I am accessing the static variable outside You're not accessing it. You're _defining_ it "outside". Using it "inside" should be fine. Uncomment the statement where you're using it and you will see that it's still OK. Quote: ------------------------------------------------------------- class A { private: public: static int a; static float f() { return 3.14;} }; int A::a = -1; Now it's fine. Here you defined it. It wasn't here before, was it? Quote: int main () { // A::a = -1; float g = A::f(); cout << g << endl; cin >> g; return 0 ; } ------------------------------------------------------------- Back to top Rolf Magnus Guest Posted: Fri Apr 29, 2005 3:19 pm    Post subject: Re: static member function MJ wrote: Quote: Hi I am reading scott mayor and thinking in C++ vol i and II Sorry I could not get what you mean ... I have declared the static data member in the class itself.. Yes. You have _declared_, but not _defined_ it there. Quote: and I can do like that .. whats wrong in that .... See the code below it works fine when I am accessing the static variable outside You're not _accessing_ it, you're _defining_ it. Now that it's defined, it should be accessible from within main. Quote: ------------------------------------------------------------- class A { private: public: static int a; static float f() { return 3.14;} }; int A::a = -1; int main () { // A::a = -1; float g = A::f(); cout << g << endl; cin >> g; return 0 ; } ------------------------------------------------------------- MJ Back to top MJ Guest Posted: Fri Apr 29, 2005 3:23 pm    Post subject: Re: static member function Hi I had tried that ... removing the *int* but the code does not work... regarding the initialization ... the static variables get initialized to zero... see the code below ----------------------------------------------- static k; int main () { cout << k << endl; return 0 ; } ---------------------------------------------------- this will print the value of k = 0.... so the static k will get initialized at the time of compilation.... But I am not sure what happens to the static variable in a class ... MJ Back to top MJ Guest Posted: Fri Apr 29, 2005 3:29 pm    Post subject: Re: static member function Hi Yes I got it It was a mistake I did .... the static variable should be defined outside the scope of the class ... in case of global static variable they get defined and declared .... I tried and its working fine the code is as -------------------------------------- class A { private: public: static int a; static float f() { A::a = 10; //cout << a << endl; return 3.14; } }; int A::a;// = -1; int main () { A::a = -10; float g = A::f(); cout << A::a << endl; cin >> g; return 0 ; } ------------------------------------------------ This code is working fine .... Thanks a lot MJ ..... 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