C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  static data type and initialization issues          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Bhavesh Goswami Guest Posted: Mon Mar 28, 2005 11:57 am    Post subject: static data type and initialization issues Hey, I was surprised to find recently that you cannot use static datatype without initializing it (I though it was automatically initialized to zero). The below is a very small sample program from a c++ book.. _______ #include <stdio.h> class gamma{ private: static int total; int id; public: gamma() { total++; id = total; } static void showtotal() { printf("nTotal is %dn", total); } }; int gamma::total = 0; //the program will not compile without this line void main() { gamma g1; g1.showtotal(); } ___________________ If I remove the line "int gamma::total=0;", then the .NET complier and also gcc compiler on solaris gives linker error like "cannot find gamma::total". I referenced two book and previous posts but cannot find explanation on why this might be happening.. Any inputs to help me understand the whole deal will be really appreciated. Thanks, Bhavesh [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Steffen Jakob Guest Posted: Mon Mar 28, 2005 5:22 pm    Post subject: Re: static data type and initialization issues On Mon, 28 Mar 2005 06:57:39 -0500, Bhavesh Goswami wrote: Quote: Hey, I was surprised to find recently that you cannot use static datatype without initializing it (I though it was automatically initialized to zero). The below is a very small sample program from a c++ book.. // ... Quote: If I remove the line "int gamma::total=0;", then the .NET complier and also gcc compiler on solaris gives linker error like "cannot find gamma::total". I referenced two book and previous posts but cannot find explanation on why this might be happening.. Any inputs to help me understand the whole deal will be really appreciated. From the ISO Standard: 9.4.2: "The declaration of a static data member in its class definition is not a definition and may be of an incomplete type other than cv-qualified void. The definition for a static data member shall appear in a namespace scope enclosing the member's class definition. In the definition at namespace scope, the name of the static data member shall be qualified by its class name using the :: operator." ... Greetings, Steffen. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Peter C. Chapin Guest Posted: Mon Mar 28, 2005 5:25 pm    Post subject: Re: static data type and initialization issues "Bhavesh Goswami" <bhavesh0007 (AT) yahoo (DOT) com> wrote in news:1111975409.303963.194750 (AT) g14g2000cwa (DOT) googlegroups.com: Quote: If I remove the line "int gamma::total=0;", then the .NET complier and also gcc compiler on solaris gives linker error like "cannot find gamma::total". I referenced two book and previous posts but cannot find explanation on why this might be happening.. Any inputs to help me understand the whole deal will be really appreciated. It's not the explicit initialization that it needs, but rather the definition. When you declare a static data member of a class, it is only a *declaration*. To entice the compiler to actually set aside storage for the static member you must *define* it. That's the purpose of the line the compiler complains about when you remove. Peter [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thomas Maeder Guest Posted: Mon Mar 28, 2005 5:33 pm    Post subject: Re: static data type and initialization issues "Bhavesh Goswami" <bhavesh0007 (AT) yahoo (DOT) com> writes: Quote: I was surprised to find recently that you cannot use static datatype without initializing it (I though it was automatically initialized to zero). The below is a very small sample program from a c++ book.. <picking nits> Your question is not about a static type, but about a static object. </picking nits> Quote: class gamma{ private: static int total; This is the declaration of a static data member. It tells the public that if a member named total of class gamma is accessed, it's static and of type int. It's no definition, though. No memory is allocated for gamma::total. Quote: }; int gamma::total = 0; //the program will not compile without this line This is the definition the the static data member gamma::total. The member can only be accessed (or have its address taken) if the program contains such a definition in one of the translation units. This definition is equivalent to int gamma::total; because, as you write, static data is zero-initalized by default. Quote: void main() A Standard conforming compiler should issue a diagnostic here. The return type of main() has to be int. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top comp.ai.games Guest Posted: Mon Mar 28, 2005 11:51 pm    Post subject: Re: static data type and initialization issues Thanks to all those who replied. A part of my question was that I referenced a few books including, "Turbo C++" by Robert Lafore and "Teach yourself C++ ...." by Jesse liberty and also a few web resources and they have no mention of such a thing. Infact the code mentioned in the post comes straight out of a book (with some pruning for simplicity). Is this a recent amendment or is it compiler and books catching up with actual standards ??? Thanks Bhavesh Ps: on other note, is the need for main to have return type int a standard or good practice ? [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Shantanu Garg Guest Posted: Tue Mar 29, 2005 9:31 am    Post subject: Re: static data type and initialization issues Quote: Ps: on other note, is the need for main to have return type int a standard or good practice ? 'main' should have a return type of 'int' and tt is in standard. On the otherhand, you dont need to explicitely return a value from 'main'. A default one is generated implicitely. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. 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