C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Overloading + Operator          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message - Steve - Guest Posted: Tue Jul 29, 2003 4:21 am    Post subject: Overloading + Operator If you want to see all the code it's at http://planetevans.com/c However I think I have all the relevant parts here. main() makes the following call IntArray c = a + b; // IntArray is my class I have overloaded the + operator like this. IntArray& IntArray::operator+(IntArray &addThis) { IntArray temp(arrayHigh-arrayLow); for(int i=temp.low();i temp[i]=array[arrayLow+i]+addThis.array[addThis.arrayLow+i]; return temp; } However it doesn't appear that when the c= part of the line executes that the temp array is following it. I assume that is becuase temp follows out of scope and the destructor is called, that does a delete array[]. What should I do? Back to top Alf P. Steinbach Guest Posted: Tue Jul 29, 2003 4:38 am    Post subject: Re: Overloading + Operator On Tue, 29 Jul 2003 04:21:31 GMT, "- Steve -" <sevans (AT) foundation (DOT) sdsu.edu> wrote: Quote: If you want to see all the code it's at http://planetevans.com/c However I think I have all the relevant parts here. main() makes the following call IntArray c = a + b; // IntArray is my class The critical thing here is the design, namely What should happen if a and b have different array bounds? - Notion of infinite array "extension"? - Exception in all cases? - Exception only if _sizes_ are different? Quote: I have overloaded the + operator like this. IntArray& IntArray::operator+(IntArray &addThis) This is a member function, conceptually for adding something _into_ an existing array, which is modified by that operation. That doesn't correspond to the usual semantics of '+'. Instead, call this member function 'add', and use it as just a helper in operator '+'. Let operator '+' be a free-standing function, and let it be a 'friend' of IntArray if necessary. Quote: { IntArray temp(arrayHigh-arrayLow); See the comment above about the design, which you should resolve first of all. Quote: for(int i=temp.low();i temp[i]=array[arrayLow+i]+addThis.array[addThis.arrayLow+i]; return temp; Here the code returns a reference to a variable 'temp' that is destroyed by the time control goes back to the caller. Quote: } However it doesn't appear that when the c= part of the line executes that the temp array is following it. I assume that is becuase temp follows out of scope and the destructor is called Yes. Quote: that does a delete array[]. Probably, if that's what you have in the destructor. Quote: What should I do? See above. Summary: rename your current operator to 'add', let the return type of that be either 'void' or else return reference to '*this', add a friend operator '+' of two arguments which returns IntArray by value, but first of all and most important, resolve the design question noted above. Back to top - Steve - Guest Posted: Tue Jul 29, 2003 4:45 am    Post subject: Re: Overloading + Operator Well that's another problem I have to deal with. Right now if a IntArray object is created with no arguments then it creates an array going from 0 to 9. So that's what is happening here I assume becuase there is no arguments on the decleration. if "a" and "b" only need to be of the same size array. So if a was 1 to 4, and b was 5 to 6. Then it would go a[1] + b[5], a[2] + b[6], etc, etc. Steve "Alf P. Steinbach" <alfps (AT) start (DOT) no> wrote Quote: On Tue, 29 Jul 2003 04:21:31 GMT, "- Steve -" wrote: If you want to see all the code it's at http://planetevans.com/c However I think I have all the relevant parts here. main() makes the following call IntArray c = a + b; // IntArray is my class The critical thing here is the design, namely What should happen if a and b have different array bounds? - Notion of infinite array "extension"? - Exception in all cases? - Exception only if _sizes_ are different? I have overloaded the + operator like this. IntArray& IntArray::operator+(IntArray &addThis) This is a member function, conceptually for adding something _into_ an existing array, which is modified by that operation. That doesn't correspond to the usual semantics of '+'. Instead, call this member function 'add', and use it as just a helper in operator '+'. Let operator '+' be a free-standing function, and let it be a 'friend' of IntArray if necessary. { IntArray temp(arrayHigh-arrayLow); See the comment above about the design, which you should resolve first of all. for(int i=temp.low();i temp[i]=array[arrayLow+i]+addThis.array[addThis.arrayLow+i]; return temp; Here the code returns a reference to a variable 'temp' that is destroyed by the time control goes back to the caller. } However it doesn't appear that when the c= part of the line executes that the temp array is following it. I assume that is becuase temp follows out of scope and the destructor is called Yes. that does a delete array[]. Probably, if that's what you have in the destructor. What should I do? See above. Summary: rename your current operator to 'add', let the return type of that be either 'void' or else return reference to '*this', add a friend operator '+' of two arguments which returns IntArray by value, but first of all and most important, resolve the design question noted above. Back to top John Harrison Guest Posted: Tue Jul 29, 2003 6:08 am    Post subject: Re: Overloading + Operator "- Steve -" <sevans (AT) foundation (DOT) sdsu.edu> wrote Quote: If you want to see all the code it's at http://planetevans.com/c However I think I have all the relevant parts here. main() makes the following call IntArray c = a + b; // IntArray is my class I have overloaded the + operator like this. IntArray& IntArray::operator+(IntArray &addThis) The usual way to overload operator+ is as a two parameter non-member function, i.e. friend IntArray operator+(const IntArray& x, const IntArray& y); This adds two arrays and returns a third array (note the return type is not a reference). What you have written is more like operator+= i.e. add something to an existing array, return a reference to that existing array (i.e. return *this). Decide which you want first of all. Also you missed const, on addThis IntArray& IntArray::operator+=(const IntArray &addThis) john Back to top John Dibling Guest Posted: Tue Jul 29, 2003 4:11 pm    Post subject: Re: Overloading + Operator On Tue, 29 Jul 2003 04:21:31 GMT, "- Steve -" <sevans (AT) foundation (DOT) sdsu.edu> wrote: Quote: What should I do? You should make IntArrya::operator+() operate on the 'this' pointer rather than a temporary variable. </dib> John Dibling Witty banter omitted for your protection Back to top Victor Bazarov Guest Posted: Tue Jul 29, 2003 4:18 pm    Post subject: Re: Overloading + Operator "- Steve -" <sevans (AT) foundation (DOT) sdsu.edu> wrote... Quote: "John Harrison" <john_andronicus (AT) hotmail (DOT) com> wrote in message news:bg530u$4u9jl$1 (AT) ID-196037 (DOT) news.uni-berlin.de... The usual way to overload operator+ is as a two parameter non-member function, i.e. friend IntArray operator+(const IntArray& x, const IntArray& y); This adds two arrays and returns a third array (note the return type is not a reference). What you have written is more like operator+= i.e. add something to an existing array, return a reference to that existing array (i.e. return *this). Decide which you want first of all. Also you missed const, on addThis IntArray& IntArray::operator+=(const IntArray &addThis) john I tried adding friend IntArray operator+(const IntArray& x, const IntArray& y) as a function of the class, and outside of the class. Either way at complie time I'm told 'operator`+'' : a friend function can only be declared in a class. Of course. The declaration statement John posted (the one with the 'friend' keyword in it) should go inside the IntArray class definition. You still should define the function outside (and that definition should not contain the 'friend' keyword because it makes no sense not within a class). What does your book say about 'friend' specifier? You don't expect those who respond to your posts to tie your shoes for you as well, do you? Victor Back to top Karl Heinz Buchegger Guest Posted: Wed Jul 30, 2003 9:00 am    Post subject: Re: Overloading + Operator John Dibling wrote: Quote: On Tue, 29 Jul 2003 04:21:31 GMT, "- Steve -" [email]sevans (AT) foundation (DOT) sdsu.edu[/email]> wrote: What should I do? You should make IntArrya::operator+() operate on the 'this' pointer rather than a temporary variable. Please analyze the code better. He already does this: Quote: temp[i]=array[arrayLow+i]+addThis.array[addThis.arrayLow+i]; array is a member variable to the IntArray object. Granted: some whitespace characters would have made this more obvious: Quote: for( int i = temp.low(); i < temp.high(); ++i ) temp[i] = array[ arrayLow+i ] + addThis.array[ addThis.arrayLow+i ]; The OP's problem is that he returned a reference, when he should return an object. -- Karl Heinz Buchegger [email]kbuchegg (AT) gascad (DOT) at[/email] 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 (comp.lang.c++) 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.