C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  const and standard types          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message cppsks Guest Posted: Wed Aug 25, 2004 7:29 pm    Post subject: const and standard types What would be the rational for using const with standard types? const int & OR const unsigned long & Thanks. Back to top Victor Bazarov Guest Posted: Wed Aug 25, 2004 8:01 pm    Post subject: Re: const and standard types cppsks wrote: Quote: What would be the rational for using const with standard types? const int & OR const unsigned long & Often a const reference to one of built-in types happens to be used in template code, like template <class T> void foo(T const& blah); ... foo(42); Nothing bad about it, AFAIK. I once did some testing and figured that passing 'double' by value was just slightly slower than passing it by a ref or by a pointer, but only in a debug version (or something like that). My rule is, "when in doubt, test". My other rule is, "for built-in types, pass by value". Victor Back to top Andrey Tarasevich Guest Posted: Wed Aug 25, 2004 11:00 pm    Post subject: Re: const and standard types cppsks wrote: Quote: What would be the rational for using const with standard types? const int & OR const unsigned long & ... Hmm... What kind of answer do you expect besides the obvious "to declare objects of standard types as constants"? The implications of declaring an object of standard type as constant are numerous. Constant objects of integral type can be used in integral constant expressions, while non-constant objects can't: const int a = 5; int b = 5; char aa[a]; // OK char bb[b]; // ERROR Const-qualified references to standard types can be bound to rvalue objects: const int& cr = 5; // OK int& r = 5; // ERROR And so on... -- Best regards, Andrey Tarasevich Back to top Rolf Magnus Guest Posted: Thu Aug 26, 2004 12:50 am    Post subject: Re: const and standard types cppsks wrote: Quote: What would be the rational for using const with standard types? Just the same as for using it with your own types. Quote: const int & OR const unsigned long & Did you make references here for a reason? Back to top Siemel Naran Guest Posted: Thu Aug 26, 2004 2:59 am    Post subject: Re: const and standard types "cppsks" <sksjava (AT) hotmail (DOT) com> wrote Quote: What would be the rational for using const with standard types? const int & OR const unsigned long & It can happen as part of implicit tempalte instantiation. template <class T> void print(const T&); For an explicit function, I'd probably pass by value as in the release build it would probably be faster because the compiler could optimize without having to worry about aliasing. See Victor's post too. If you have a function and it receives a variable by value, but in the function definition you declare the value const, that's another story. Is this what you're asking about? void f(int); void f(const int i) { ... } Back to top cppsks Guest Posted: Sat Aug 28, 2004 4:16 am    Post subject: Re: const and standard types "Siemel Naran" <SiemelNaran (AT) REMOVE (DOT) att.net> wrote Quote: "cppsks" <sksjava (AT) hotmail (DOT) com> wrote in message news:cgipa9$203$1 (AT) news (DOT) lsil.com... If you have a function and it receives a variable by value, but in the function definition you declare the value const, that's another story. Is this what you're asking about? void f(int); void f(const int i) { ... } Thanks for the response to all. Just a quick question about the above declartion and definition. What does the above convention mean? Thanks, skscpp Back to top Siemel Naran Guest Posted: Sat Aug 28, 2004 4:54 am    Post subject: Re: const and standard types "cppsks" <sksjava (AT) hotmail (DOT) com> wrote Quote: "Siemel Naran" <SiemelNaran (AT) REMOVE (DOT) att.net> wrote in message void f(int); void f(const int i) { ... } Thanks for the response to all. Just a quick question about the above declartion and definition. What does the above convention mean? Usually we declare the function variables without top-level const, but may define them with const to prevent us from accidentally changing the variable, and making it clear to the person reading the code that in the body of function f, variable 'i' will not change its value. Doubtless, this practice is useless for short functions which are simple to understand anyway, but does pay off in larger and/or complicated functions. 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.