From 1454777776533923675 X-Google-Language: ENGLISH,ASCII-7-bit X-Google-Thread: f78e5,add62e0f5e586127 X-Google-Attributes: gidf78e5,public X-Google-ArrivalTime: 1994-09-26 03:49:49 PST Newsgroups: comp.std.c++ Path: bga.com!news.sprintlink.net!howland.reston.ans.net!EU.net!uknet!festival!dcs.ed.ac.uk!cnews From: ddr@dcs.ed.ac.uk (Douglas Rogers) Subject: Re: compile time consts In-Reply-To: rfg@netcom.com's message of Sat, 24 Sep 1994 07:54:40 GMT Message-ID: Sender: cnews@dcs.ed.ac.uk (UseNet News Admin) Organization: Department of Computer Science, Edinburgh University References: <1994Sep19.110228.3591@fmrco.uucp> Date: Mon, 26 Sep 1994 09:56:31 GMT Lines: 61 Ronald F Guilmette writes: In article rfg@netcom.com (Ronald F. Guilmette) writes: rfg> In article weissman@netcom.com rfg> (Bob Weissman) writes: >> Because "(int) sqrt((double) N)" is not a constant-expression, >> neither is "Q". rfg> Can _anyone_ provide a chapter and verse citation to support this rfg> conclusion? If so, I would greatly appreciate it. Thanks. Unfortunately I don't have a copy of the draft standard, and I can find no mention of the problem or suitable exasmples in the ARM but the implication is that the compiler may need some compile time capability to evaluate expressions. The idea of const in C++ is to enable a const value to be used within a static decleration. in C this is illegal but in C++ encouraged:- const int MAX_STRING = 61; char string[MAX_STRING]; Now this form is not in dispute, in C this is not a problem as #define is used ie:- #define MAX_STRING 61 char string[MAX_STRING]; No worries, but now if we use an expression, in C the rules are clear, the preprocessor must have certain mathematical capability ie:- #define STRING_LEN 60 #define MAX_STRING STRING_LEN + 1; char string[MAX_STRING]; If we do the same in C++ then we need to know - what expressions can be evaluated at compile time. Can this be? const int STRING_LEN = 60; const int MAX_STRING = STRING_LEN + 1; Does this only apply to built in types? What about expressions in the standard library as in the example above? -- Douglas --- ============================================================================= Douglas Rogers MAIL: ddr@dcs.ed.ac.uk Tel: +44 31-650 5172 (direct dial) Fax: +44 31-667 7209 ============================= Mostly harmless ===============================