C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  const follow the member function          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message avier Guest Posted: Sat Jul 30, 2005 10:44 am    Post subject: const follow the member function Hello, I was reading the C++ codes and was confused by the following: double expect (double t, double x, double dt) const { return x + t*dt; } Does the "const" in the member function follow the function name mean the returned double cannot be modified? Rookie question, thanks for your help in advance. Back to top Stu Guest Posted: Sat Jul 30, 2005 11:06 am    Post subject: Re: const follow the member function avier wrote: Quote: Hello, I was reading the C++ codes and was confused by the following: double expect (double t, double x, double dt) const { return x + t*dt; } Does the "const" in the member function follow the function name mean the returned double cannot be modified? Rookie question, thanks for your help in advance. It means that the member function does not modify the class object it is a member of. Stu Back to top avier Guest Posted: Sat Jul 30, 2005 11:26 am    Post subject: Re: const follow the member function hi stu, thanks for the prompt help. Does it mean that the data in the object will not be modified? Back to top Maxim Yegorushkin Guest Posted: Sat Jul 30, 2005 12:29 pm    Post subject: Re: const follow the member function avier wrote: Quote: hi stu, thanks for the prompt help. Does it mean that the data in the object will not be modified? It does not. const for member function is just a hint to the reader that the function does not change logical state of an object, although object's physical state (the bits it's comprised of) may well change. Back to top Alipha Guest Posted: Sat Jul 30, 2005 5:25 pm    Post subject: Re: const follow the member function avier wrote: Quote: Hello, I was reading the C++ codes and was confused by the following: double expect (double t, double x, double dt) const { return x + t*dt; } Does the "const" in the member function follow the function name mean the returned double cannot be modified? Rookie question, thanks for your help in advance. read: http://www.parashift.com/c++-faq-lite/const-correctness.html sections 18.10-18.13 in particular Back to top avier Guest Posted: Sat Jul 30, 2005 7:06 pm    Post subject: Re: const follow the member function Again, thanks Maxim and Alipha! Back to top John Carson Guest Posted: Sun Jul 31, 2005 3:01 am    Post subject: Re: const follow the member function "Maxim Yegorushkin" <maxim.yegorushkin (AT) gmail (DOT) com> wrote Quote: avier wrote: hi stu, thanks for the prompt help. Does it mean that the data in the object will not be modified? It does not. const for member function is just a hint to the reader that the function does not change logical state of an object, although object's physical state (the bits it's comprised of) may well change. It is far more than a hint. 1. It is a promise that the function won't modify the object's data unless that data is declared mutable --- a promise that the compiler will enforce. 2. It is a required promise for any function that is called on a const object --- a requirement that, once again, the compiler will enforce. For 1., observe that the following won't compile because Set changes the object in spite of promising not to: class Test { int x; public: Test() : x(0) {} void Set(int x_) const { x = x_; // won't compile; violates the const promise } }; For 2., observe that the following won't compile because of the absence of the const qualifier on the DoNothing function, i.e., the fact that the DoNothing function does nothing is insufficient; it must declare this fact with the const keyword: class Test { public: Test() {} void DoNothing() {} }; int main() { const Test t; t.DoNothing(); //won't compile; t is declared const but DoNothing isn't return 0; } -- John Carson Back to top avier Guest Posted: Thu Aug 04, 2005 11:16 am    Post subject: Re: const follow the member function thanks, it really hepls! 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.