C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Why we need classes Goto page 1, 2  Next          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Pratts Guest Posted: Mon Feb 28, 2005 3:34 am    Post subject: Why we need classes I am a new one who have joined u plz try to help me bcoz i could not find ny sutiable answer foer this Question Qus>>why do we need classes when structures provide similar functionality?? Back to top Kelly Mandrake Guest Posted: Mon Feb 28, 2005 3:41 am    Post subject: Re: Why we need classes structures are public by default and classes are private by default. Unless you use the keywords private, public or protected, any member funtions or member data in a structure will be public. The idea behind encapsulation is to hide the details, it is desireable to make private data and provide public interface methods that the user of the class can use. Back to top Jack Klein Guest Posted: Mon Feb 28, 2005 4:15 am    Post subject: Re: Why we need classes On 27 Feb 2005 19:34:41 -0800, "Pratts" <its_prateek (AT) rediffmail (DOT) com> wrote in comp.lang.c++: Quote: I am a new one who have joined u plz try to help me bcoz i could not find ny sutiable answer foer this Question Qus>>why do we need classes when structures provide similar functionality?? A better way to ask this question would be: "Why do we need structs in C++ when we have classes?" There is a difference in default access, but this is really trivial. Structs are needed for backwards compatibility with C code, of which there were millions of lines in existence as C++ came into being. Classes are little more than a documentation mechanism. -- Jack Klein Home: http://JK-Technology.Com FAQs for comp.lang.c http://www.eskimo.com/~scs/C-faq/top.html comp.lang.c++ http://www.parashift.com/c++-faq-lite/ alt.comp.lang.learn.c-c++ http://www.contrib.andrew.cmu.edu/~ajo/docs/FAQ-acllc.html Back to top osmium Guest Posted: Mon Feb 28, 2005 4:25 am    Post subject: Re: Why we need classes "Pratts" writes: Quote: I am a new one who have joined u plz try to help me bcoz i could not find ny sutiable answer foer this Question Qus>>why do we need classes when structures provide similar functionality?? If you mean why do we need the keyword "class" in addition to stuct, the answer is, we don't. It's just for convenience and, as typically used, improves documentation. Back to top DHOLLINGSWORTH2 Guest Posted: Mon Feb 28, 2005 7:29 am    Post subject: Re: Why we need classes "Pratts" <its_prateek (AT) rediffmail (DOT) com> wrote Quote: I am a new one who have joined u plz try to help me bcoz i could not find ny sutiable answer foer this Question Qus>>why do we need classes when structures provide similar functionality?? structures do not provide anywhere near the functionality you get from classess. Classess have constructors, that can be modified./overloaded. Classes have destructors, that can be modified/ overloaded. Classes allow for operator Overloads. Classes have member functions, static functions. Public, Private, and Protected Data and code. Classes incapsulate. Structures Arrange. The differences are vast. You will have to write some code to begin to understand the impact. I struggled with it for several months. You gain Power, Robustness. A level of Protection, while increasing the longevity of your code. I can send you some examples done with both structures and class object, if you'd like to see the difference. dan [email]DHOLLINGSWORTH2 (AT) cox (DOT) net[/email] Back to top 440gtx@email.com Guest Posted: Mon Feb 28, 2005 8:49 am    Post subject: Re: Why we need classes Quote: Classess have constructors, that can be modified./overloaded. Classes have destructors, that can be modified/ overloaded. Classes allow for operator Overloads. Classes have member functions, static functions. Public, Private, and Protected Data and code. Classes incapsulate. Structures Arrange. struct was upgraded in C++ and can do all of that too. Try it. I personally stopped using the class keyword and went back to struct. The reason is I can eliminate that silly "public:" statement at the beginning needed to expose the constructor. In the end, "class" proved to be just an unnecessary annoyance with no value add for me. I do use public, protected, and private extensively to define structs. Back to top Martijn Mulder Guest Posted: Mon Feb 28, 2005 9:18 am    Post subject: Re: Why we need classes Quote: Classess have constructors, that can be modified./overloaded. Classes have destructors, that can be modified/ overloaded. Classes allow for operator Overloads. Classes have member functions, static functions. Public, Private, and Protected Data and code. Classes incapsulate. Structures Arrange. Quote: struct was upgraded in C++ and can do all of that too. Try it. I personally stopped using the class keyword and went back to struct. The reason is I can eliminate that silly "public:" statement at the beginning needed to expose the constructor. In the end, "class" proved to be just an unnecessary annoyance with no value add for me. I do use public, protected, and private extensively to define structs. Indeed. I think that 'class' and 'struct' where meant to be equivalent. I never touched another class after reading what Bjarne Stroustrup wrote about it in the Annotated C++ Reference Manual, Addison-Wesly Publishing Company, 1995, Paragraph 11.2: <quote> (...) For example, novices often don't know about access specifiers and get confused by this: class X { public: f(); }; class Y : X { }; // no access specifier // private by default void g(Y* p) { p->f(); // error } Even experts can get caught. A compiler can be most helpful by issuing a warning for the missing access specifier. Having private as the default was chosen to reflect the general view that things that are not explicitly declared public are private. Defining a default access specifier was probably a mistake. </quote> He says that the default access specifier 'private' for classes was a mistake. There should have been _no_ default access specifier, ie class should be 'public' by default, just like struct is. The difference between class and struct is based on a mistake. A class was meant to act just like a struct does. Back to top Howard Guest Posted: Mon Feb 28, 2005 4:22 pm    Post subject: Re: Why we need classes "Pratts" <its_prateek (AT) rediffmail (DOT) com> wrote Quote: I am a new one who have joined u plz try to help me bcoz i could not find ny sutiable answer foer this Question Qus>>why do we need classes when structures provide similar functionality?? we r n nglsh lang nwsgrp her, not IM try complt wrds nxt tm Back to top Pratts Guest Posted: Thu Mar 10, 2005 5:12 am    Post subject: Re: Why we need classes buddy very sorry to say that u must go through the things again bcoz structures can do all that constructor destructors operator Overloads and every thing that class can do plz try this out byEEEEEEEEEEE Back to top DHOLLINGSWORTH2 Guest Posted: Fri Mar 11, 2005 5:12 am    Post subject: Re: Why we need classes "Pratts" <its_prateek (AT) rediffmail (DOT) com> wrote Quote: buddy very sorry to say that u must go through the things again bcoz structures can do all that constructor destructors operator Overloads and every thing that class can do plz try this out byEEEEEEEEEEE Can structures have pure virtual Functions? Can a structure prevent a programmer from erroneously ovewriting data elements? Can a structure have Private data? Can a structure have Protected data? The truth is I'm not sure, I use structs to set up Common data that the Class objects will be using, and sharing with the outside world. Back to top Karl Heinz Buchegger Guest Posted: Fri Mar 11, 2005 9:55 am    Post subject: Re: Why we need classes DHOLLINGSWORTH2 wrote: Quote: "Pratts" <its_prateek (AT) rediffmail (DOT) com> wrote in message news:1110431570.048996.266740 (AT) l41g2000cwc (DOT) googlegroups.com... buddy very sorry to say that u must go through the things again bcoz structures can do all that constructor destructors operator Overloads and every thing that class can do plz try this out byEEEEEEEEEEE Can structures have pure virtual Functions? Can a structure prevent a programmer from erroneously ovewriting data elements? Can a structure have Private data? Can a structure have Protected data? The answer to all your questions is a loud and sound: Yes -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] Back to top Jerry Coffin Guest Posted: Fri Mar 11, 2005 5:29 pm    Post subject: Re: Why we need classes DHOLLINGSWORTH2 wrote: [ ... ] Quote: structures do not provide anywhere near the functionality you get from classess. Not true. Quote: Classess have constructors, that can be modified./overloaded. Classes have destructors, that can be modified/ overloaded. Classes allow for operator Overloads. Classes have member functions, static functions. Public, Private, and Protected Data and code. Classes incapsulate. Structures Arrange. In C++, all of the above statements apply equally to structs as classes. The ONLY difference between a struct and a class in C++ is the default visibility (private for class, public for struct). C++ allows structs to have ctors, dtors, operator overloads, member functions and public, private and protected members. You can derive one struct from another struct, or even derive a struct from a class or a class from a struct. As an aside: destructors are only _rarely_ overloaded, and there are only two overloads: one that is used when exiting a placement new via an exception, and the usual one (no parameters, no cv-qualifiers) that's used all the rest of the time. -- Later, Jerry. The universe is a figment of its own imagination. Back to top Larry Brasfield Guest Posted: Fri Mar 11, 2005 5:44 pm    Post subject: Re: Why we need classes "Jerry Coffin" <jcoffin (AT) taeus (DOT) com> wrote .... Quote: As an aside: destructors are only _rarely_ overloaded, and there are only two overloads: one that is used when exiting a placement new via an exception, and the usual one (no parameters, no cv-qualifiers) that's used all the rest of the time. In fact, '_rarely_' is never. You are thinking of the operator delete overload that will (or should) match an operator new used in a placement new. The only time destructors are run automatically by a correct C++ compiler is after construction of the object has successfully completed. There is no such thing as an overloaded destructor. -- --Larry Brasfield email: [email]donotspam_larry_brasfield (AT) hotmail (DOT) com[/email] Above views may belong only to me. Back to top Howard Guest Posted: Fri Mar 11, 2005 5:52 pm    Post subject: Re: Why we need classes "Larry Brasfield" <donotspam_larry_brasfield (AT) hotmail (DOT) com> wrote Quote: "Jerry Coffin" <jcoffin (AT) taeus (DOT) com> wrote in message news:1110562149.085576.244920 (AT) g14g2000cwa (DOT) googlegroups.com... ... The only time destructors are run automatically by a correct C++ compiler is after construction of the object has successfully completed. Hmmm, so when I successfully create an object, the destructor is called? That kind of screws up my whole design... I was planning on using those newly constructed objects! Care to re-word that, or explain what you mean a little better? -Howard Back to top Larry Brasfield Guest Posted: Fri Mar 11, 2005 5:59 pm    Post subject: Re: Why we need classes "Howard" <alicebt (AT) hotmail (DOT) com> wrote Quote: "Larry Brasfield" <donotspam_larry_brasfield (AT) hotmail (DOT) com> wrote "Jerry Coffin" <jcoffin (AT) taeus (DOT) com> wrote in message news:1110562149.085576.244920 (AT) g14g2000cwa (DOT) googlegroups.com... ... The only time destructors are run automatically by a correct C++ compiler is after construction of the object has successfully completed. Hmmm, so when I successfully create an object, the destructor is called? That kind of screws up my whole design... I was planning on using those newly constructed objects! Care to re-word that, or explain what you mean a little better? (I might suggest you read more carefully. ;-) Q. When are destructors ever run automatically? A. Sometime after successfull construction of temporary objects and auto storage class objects. I did not say that destructors are run automatically upon all successfully constructed objects, nor did I suggest they are run immediately after construction. So you can go ahead and keep using your objects! My statement could have been more clearly written. -- --Larry Brasfield email: [email]donotspam_larry_brasfield (AT) hotmail (DOT) com[/email] Above views may belong only to me. 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