C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Write your own "new" operator          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message Rohit Dhamija Guest Posted: Mon Jul 19, 2004 10:20 am    Post subject: Write your own "new" operator Dear ALL, How can we write our own "new operator" ? e.g. i have a class A and i want to create a object on heap so inspite of allocating memory using new i want to create my own function to simulate new operator. Are following steps sufficient: a) compute the size of the class using the number of variables available( But i dnot know in advance how many variables are present in the class) b) Type cast the memory to the class c) Initialize values of the class And then access the variables of the class by taking a pointer to that class and access the corresponding values. Also, correct me in above steps if i am wrong. Please suggest. Regards, Rohit [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Thomas Richter Guest Posted: Mon Jul 19, 2004 5:28 pm    Post subject: Re: Write your own "new" operator Hi, Quote: How can we write our own "new operator" ? Add the members "operator new" and "operator new[]" to your class, with matching delete operators. Quote: Are following steps sufficient: a) compute the size of the class using the number of variables available( But i dnot know in advance how many variables are present in the class) b) Type cast the memory to the class c) Initialize values of the class And then access the variables of the class by taking a pointer to that class and access the corresponding values. All these steps have to be carried out by the compiler, actually, in a "new expression" and will call your "operator new" with the proper arguments, namely the size of the memory chunk to be allocated. Afterwards, the constructor of the object is called, and it is supposed to initialize the object correctly. There's no need for casting, and no need to do this "manually", except for a proper implementation of the constructor and operator new. So long, Thomas [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Andrea Griffini Guest Posted: Mon Jul 19, 2004 8:58 pm    Post subject: Re: Write your own "new" operator On 19 Jul 2004 06:20:49 -0400, [email]rohit_dhamija (AT) rediffmail (DOT) com[/email] (Rohit Dhamija) wrote: Quote: Dear ALL, How can we write our own "new operator" ? You can do two different things; one is writing a custom allocator for a specific class so that when the C++ expression "new MyClass(...)" is evaluated the custom allocator is called to get the memory; the other possibility is redefining the global allocator so that when someone needs memory for *any* class using "new xxx(...)" that allocator is called. Quote: e.g. i have a class A and i want to create a object on heap so inspite of allocating memory using new i want to create my own function to simulate new operator. I don't understand what you mean with that "so" before "inspite". To allocate an object on the heap there's no need to define a custom allocator (if I understand what you mean with heap). Quote: Are following steps sufficient: a) compute the size of the class using the number of variables available( But i dnot know in advance how many variables are present in the class) Knowing the "variables" defining the class is at the same time not enough and pointless. It's not enough because the size of an instance of a class is *NOT* the sum of the sizes of the "variables" in it. It's pointless because C++ is happy to tell you what is the size of a class instance (sizeof operator). Quote: b) Type cast the memory to the class No need to do that. There's not even need to use typecasts on the pointers to allocate objects on the heap or defining custom allocators. All the needed casts are done by the C++ language itself in the "new" operator. Quote: c) Initialize values of the class Hmmm... that's what a constructor is for... Quote: And then access the variables of the class by taking a pointer to that class and access the corresponding values. If you're going to fiddle with the values from the outside, and you don't have even a constructor... why are you using a class ? Quote: Also, correct me in above steps if i am wrong. Please suggest. My suggestion is to start with C++ from a good reading. C++ is an *horrible* language if you wanna learn it with just exprimentation. Believe me... it's an ugly monster done that way. I saw it ;-) HTH Andrea [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Maciej Sobczak Guest Posted: Mon Jul 19, 2004 8:59 pm    Post subject: Re: Write your own "new" operator Hi, Rohit Dhamija wrote: Quote: Dear ALL, How can we write our own "new operator" ? You may find the "Effective C++" by Scott Meyers (in particular, Items 7-10) very informative on this subject. There are many issues to consider and many pitfalls you have to avoid - it will certainly be a good idea to learn about them. -- Maciej Sobczak : http://www.msobczak.com/ Programming : http://www.msobczak.com/prog/ [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Rohit Dhamija Guest Posted: Tue Jul 27, 2004 11:01 am    Post subject: Re: Write your own "new" operator Thanks all, but i was in process of writing my own memory routines and wanted to avoid new. And donot wanted to use constructor also.... In that case are my four points to create functinality similar to new valid ? Rohit Maciej Sobczak <no.spam (AT) no (DOT) spam.com> wrote Quote: Hi, Rohit Dhamija wrote: Dear ALL, How can we write our own "new operator" ? You may find the "Effective C++" by Scott Meyers (in particular, Items 7-10) very informative on this subject. There are many issues to consider and many pitfalls you have to avoid - it will certainly be a good idea to learn about them. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Randy Maddox Guest Posted: Wed Jul 28, 2004 2:19 am    Post subject: Re: Write your own "new" operator [email]rohit_dhamija (AT) rediffmail (DOT) com[/email] (Rohit Dhamija) wrote in message news:<e77b983b.0407262111.63564671 (AT) posting (DOT) google.com>... Quote: Thanks all, but i was in process of writing my own memory routines and wanted to avoid new. And donot wanted to use constructor also.... In that case are my four points to create functinality similar to new valid ? Rohit Since this is pretty much saying "I want to use C++, but not use C++", why are you using C++? Since you want to avoid everything C++, you probably want to avoid using sizeof as well? But that would help with your point 1. Other than that, you seem to have the gist of it. But what about destruction? I presume you are as opposed to destructors as to constructors. In any case, if you bypass the C++ memory allocation routines, and bypass the C++ ctor/dtor mechanisms, what you are writing is not C++, so you really cannot expect much help from the compiler, or from this newsgroup. Good luck with it. You may want to think seriously about what you are trying to accomplish, since C++ already does what you seem to want. Randy. [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Maciej Sobczak Guest Posted: Wed Jul 28, 2004 2:53 am    Post subject: Re: Write your own "new" operator Hi, Rohit Dhamija wrote: Quote: Thanks all, but i was in process of writing my own memory routines and wanted to avoid new. I do not exactly understand but I suspect that you took it backwards... Operator new is supposed to get the memory from somewhere - it may take it from *your* memory routines. In reality, you *want* to have new, because it is part of the language and can do a lot of good stuff for you that is related to creation of objects. What you probably need is to write your own "memory routines" and have them used by operator new, so that whenever you write: A *p = new A; the memory will come from *your* memory routines, not from whenever the default implementation of new gets it. This will be hidden from the programmer - the above line of code does not show where the memory comes from. Quote: And donot wanted to use constructor also.... There is no need to avoid new and constructors. It is like removing wheels from your car - not a good idea for any real-life purpose. What exactly do you want to achieve? Do you want to write your own memory manager and plug it into the language? Or do you want to invent completely new way of creating objects? If it is somehow difficult to describe it, please try to first write a couple of lines that you would like to have working, assuming that everything is already done. This may help to pin down the goals. -- Maciej Sobczak : http://www.msobczak.com/ Programming : http://www.msobczak.com/prog/ [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Rohit Dhamija Guest Posted: Sun Aug 01, 2004 2:27 pm    Post subject: Re: Write your own "new" operator Yes, atually I want to write my own memory manager that should automatically compute the size of the structure i am defining and initialize its variable. i will not using the c++ compiler, but want to write the above functionality. And i suppose this is the functionality what new does. so in other words i want to simulate new keyword. rohit Maciej Sobczak <no.spam (AT) no (DOT) spam.com> wrote Quote: Hi, Rohit Dhamija wrote: Thanks all, but i was in process of writing my own memory routines and wanted to avoid new. I do not exactly understand but I suspect that you took it backwards... Operator new is supposed to get the memory from somewhere - it may take it from *your* memory routines. In reality, you *want* to have new, because it is part of the language and can do a lot of good stuff for you that is related to creation of objects. What you probably need is to write your own "memory routines" and have them used by operator new, so that whenever you write: A *p = new A; the memory will come from *your* memory routines, not from whenever the default implementation of new gets it. This will be hidden from the programmer - the above line of code does not show where the memory comes from. And donot wanted to use constructor also.... There is no need to avoid new and constructors. It is like removing wheels from your car - not a good idea for any real-life purpose. What exactly do you want to achieve? Do you want to write your own memory manager and plug it into the language? Or do you want to invent completely new way of creating objects? If it is somehow difficult to describe it, please try to first write a couple of lines that you would like to have working, assuming that everything is already done. This may help to pin down the goals. [ 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.