C++Talk.NET C++ language newsgroups   Archives   FAQ   Search   Memberlist   Usergroups   Register   Profile   Log in to check your private messages   Log in  Potentially evaluated expression.          C++Talk.NET Forum Index -> C++ Language (Moderated) View previous topic :: View next topic   Author Message L.Suresh Guest Posted: Thu Jan 13, 2005 5:12 pm    Post subject: Potentially evaluated expression. I'm having problems in understanding 3.2/1. "An expression is potentially evaluated unless it appears where an integral constant expression is required (see 5.19)..." Can someone give me an example of this. Let's say i define int y[20 * 5]; Is the expression 20 * 5 not evaluated then? 5.19/1 "In particular, except in sizeof expressions, functions, class objects, pointers, or references shall not be used, and assignment, increment, decrement, function-call, or comma operators shall not be used" Is the following code valid C++? It does not use a constant expression in the first place and it also uses the decrement and comma operators. int i = 8; int x[--i]; int y[--i, i + 5]; Thanks for your time. --lsu [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Victor Bazarov Guest Posted: Thu Jan 13, 2005 9:49 pm    Post subject: Re: Potentially evaluated expression. L.Suresh wrote: Quote: I'm having problems in understanding 3.2/1. "An expression is potentially evaluated unless it appears where an integral constant expression is required (see 5.19)..." Can someone give me an example of this. Let's say i define int y[20 * 5]; Is the expression 20 * 5 not evaluated then? I think "evaluation" refers to run-time. Here the constant expression is used by the compiler to determine the array size. After that is done, there is no more "expression" to talk about. Quote: 5.19/1 "In particular, except in sizeof expressions, functions, class objects, pointers, or references shall not be used, and assignment, increment, decrement, function-call, or comma operators shall not be used" Is the following code valid C++? No. Quote: It does not use a constant expression in the first place and it also uses the decrement and comma operators. int i = 8; int x[--i]; int y[--i, i + 5]; Victor [ See http://www.gotw.ca/resources/clcm.htm for info about ] [ comp.lang.c++.moderated. First time posters: Do this! ] Back to top Sebastian Redl Guest Posted: Mon Jan 17, 2005 8:01 pm    Post subject: Re: Potentially evaluated expression. L.Suresh wrote: Quote: 5.19/1 "In particular, except in sizeof expressions, functions, class objects, pointers, or references shall not be used, and assignment, increment, decrement, function-call, or comma operators shall not be used" Is the following code valid C++? It does not use a constant expression in the first place and it also uses the decrement and comma operators. C++98 doesn't allow variables to specify stack array size. So the code is invalid. Were i a constant, the code would still be invalid because --i would be attempting to modify it. -- Sebastian Redl [ 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.