C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  #define or const          C++Talk.NET Forum Index -> C++ language (comp.lang.c++) View previous topic :: View next topic   Author Message Andy White Guest Posted: Wed Jul 13, 2005 4:10 am    Post subject: #define or const What is preferable to use for constants, #defines or const identifiers. And where is it customary to place const indentifiers in your files? thanks. Back to top Steven T. Hatton Guest Posted: Wed Jul 13, 2005 4:29 am    Post subject: Re: #define or const Andy White wrote: Quote: What is preferable to use for constants, #defines or const identifiers. And where is it customary to place const indentifiers in your files? thanks. constants. -- If our hypothesis is about anything and not about some one or more particular things, then our deductions constitute mathematics. Thus mathematics may be defined as the subject in which we never know what we are talking about, nor whether what we are saying is true.-Bertrand Russell Back to top Jaspreet Guest Posted: Wed Jul 13, 2005 4:43 am    Post subject: Re: #define or const Andy White wrote: Quote: What is preferable to use for constants, #defines or const identifiers. And where is it customary to place const indentifiers in your files? thanks. I would go for constants. It would help in during debugging since the symbol table would be generated for constants. However, if you are using #defines then the replacement is done before compilation and no sysmbol table gets generated. Moreover, no typechecking is performed for them. Soo, I would suggest for constants. Back to top pven Guest Posted: Wed Jul 13, 2005 4:52 am    Post subject: Re: #define or const Andy White wrote: Quote: What is preferable to use for constants, #defines or const identifiers. And where is it customary to place const indentifiers in your files? thanks. C++ recommends the usage of constants and place them on the header file. http://www-inolab.sys.es.osaka-u.ac.jp/users/kanaya/a_better_c.html Back to top Jonathan Mcdougall Guest Posted: Wed Jul 13, 2005 5:42 am    Post subject: Re: #define or const Quote: What is preferable to use for constants, #defines or const identifiers. And where is it customary to place const indentifiers in your files? thanks. http://www.parashift.com/c++-faq-lite/newbie.html#faq-29.7 Jonathan Back to top Ali Çehreli Guest Posted: Wed Jul 13, 2005 7:17 am    Post subject: Re: #define or const "Andy White" <brighamandrew (AT) msn (DOT) com> wrote Quote: What is preferable to use for constants, #defines or const identifiers. As others have said, constants. Quote: And where is it customary to place const indentifiers in your files? thanks. A clarification to what some of the others said: don't blindly put the constants in header files. Like any other name, put them to the innermost scope possible. Only when a constant is used at more than one place, move it to an outer scope as needed. Ali Back to top WittyGuy Guest Posted: Wed Jul 13, 2005 7:18 am    Post subject: Re: #define or const Andy White wrote: Quote: What is preferable to use for constants, #defines or const identifiers. And where is it customary to place const indentifiers in your files? thanks. Though const identifier is much better in many ways like debugging, you can pass them by reference and more, in some scenarios where memory is also a constraint, #define can be used, as const may take some memory in address space. -Wg- Back to top Francis Glassborow Guest Posted: Wed Jul 13, 2005 9:43 am    Post subject: Re: #define or const In article <1121239139.558033.3790 (AT) g47g2000cwa (DOT) googlegroups.com>, WittyGuy <wittyguysuku (AT) gmail (DOT) com> writes Quote: Andy White wrote: What is preferable to use for constants, #defines or const identifiers. And where is it customary to place const indentifiers in your files? thanks. Though const identifier is much better in many ways like debugging, you can pass them by reference and more, in some scenarios where memory is also a constraint, #define can be used, as const may take some memory in address space. In practice they only take memory when you do something that involves the value having an identity such as taking its address or passing it be reference. An additional consideration is whether you are using C or C++ as the semantics of const are different (in particular, const in C++ creates a compile time constant but this is not the case in C) -- Francis Glassborow ACCU Author of 'You Can Do It!' see http://www.spellen.org/youcandoit For project ideas and contributions: http://www.spellen.org/youcandoit/projects Back to top Chris ( Val ) Guest Posted: Wed Jul 27, 2005 2:02 pm    Post subject: Re: #define or const "Francis Glassborow" <francis (AT) robinton (DOT) demon.co.uk> wrote [snip] (in particular, const in C++ creates a Quote: compile time constant but this is not the case in C) True, but even that can have it's quirks: class Array { private: const int NrElems; int MyArray[ NrElems ]; public: Array( int n ) : NrElems( n ) {} }; [C++ Error] ConstTest.cpp(: E2313 Constant expression required Cheers, Chris Val Back to top Bob Hairgrove Guest Posted: Fri Aug 05, 2005 7:56 pm    Post subject: Re: #define or const [cross-posting removed...] On Wed, 13 Jul 2005 00:17:03 -0700, Ali Çehreli <acehreli (AT) yahoo (DOT) com> wrote: Quote: A clarification to what some of the others said: don't blindly put the constants in header files. Like any other name, put them to the innermost scope possible. Only when a constant is used at more than one place, move it to an outer scope as needed. For constants needed in more than one source file, declare them with the "extern" specifier in a header file, then define their values in a separate .cpp file. For constants needed only in one source file, you should declare them as "static" directly in the .cpp source file. -- Bob Hairgrove [email]NoSpamPlease (AT) Home (DOT) com[/email] Back to top Bob Hairgrove Guest Posted: Fri Aug 05, 2005 8:14 pm    Post subject: Re: #define or const [cross-posting removed] On Wed, 27 Jul 2005 14:02:19 GMT, "Chris ( Val )" <chrisval (AT) bigpond (DOT) com.au> wrote: Quote: "Francis Glassborow" <francis (AT) robinton (DOT) demon.co.uk> wrote in message news:SoMbUcBKJO1CFwap (AT) robinton (DOT) demon.co.uk... [snip] (in particular, const in C++ creates a | compile time constant but this is not the case in C) True, but even that can have it's quirks: class Array { private: const int NrElems; int MyArray[ NrElems ]; public: Array( int n ) : NrElems( n ) {} }; [C++ Error] ConstTest.cpp(: E2313 Constant expression required Cheers, Chris Val This seems to be the Borland error message ... MSVC++ Toolkit complains about an undeclared identifier: error C2327: 'Array::NrElems' : is not a type name, static, or enumerator. error C2065: 'NrElems' : undeclared identifier. Thinking about this a little makes it clear why there is an error: each instance of "Array" would potentially have a different size, making it impossible to declare arrays of Array objects...something which is trivial to do with std::vector<>. Yet C++ objects, once they are defined, should all have the same memory requirements, and these must be known to the compiler. -- Bob Hairgrove [email]NoSpamPlease (AT) Home (DOT) com[/email] Back to top elviin Guest Posted: Fri Aug 05, 2005 11:29 pm    Post subject: Re: #define or const And what about to use namespaces? unnamed namespaces for very specific files or for example constnamespace::win::constantXY constnamespace::unix::constantXY to address a proper system dependent value. 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