| Date: | Thu, 13 Apr 2006 15:29:11 +0300 |
| From: | Diomidis Spinellis <dds@aueb.gr> |
| Organization: | Athens University of Economics and Business |
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| Newsgroups: | comp.lang.c++.moderated |
| Subject: | Re: const/define -- efficiency for simple integrals |
| References: | <1144845365.832751.189250@j33g2000cwa.googlegroups.com> |
| In-Reply-To: | <1144845365.832751.189250@j33g2000cwa.googlegroups.com> |
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studennett wrote: > Is there any difference in efficiency between (at global scope): > > static const int MAX_CHAR (1024); > > and > > #define MAX_CHAR 1024 > > I'm wondering about both time and space efficiency. I can take the > address of the static const int, so surely it must take up space. The > define is 'just a number' so doesn't have to take up any space. Is > this right? If you don't take the address of MAX_CHAR the compiler is free to optimize its storage away, and this appears to be the case with two different compilers I checked. I compiled the statement volatile int x = MAX_CHAR; and both compilers generated *exactly the same code* for the two alternatives you mentioned. GCC (version 3.4.2 g++ -O3): mov DWORD PTR _x$[esp+4], 1024 Microsoft C (version 11.00.7022; cl -Ox): movl $1024, -4(%ebp) -- Diomidis Spinellis Code Quality: The Open Source Perspective (Addison-Wesley 2006) http://www.spinellis.gr/codequality
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