Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!srhqla!demott!kdq
From: kdq@demott.com (Kevin D. Quitt)
Newsgroups: comp.lang.c
Subject: Re: When do you use const
Keywords: const, #define, C
Message-ID: <1991Feb2.181948.2147@demott.com>
Date: 2 Feb 91 18:19:48 GMT
References: <1220@tredysvr.Tredydev.Unisys.COM>
Organization: DeMott Electronics Co., Van Nuys CA
Lines: 28

In article <1220@tredysvr.Tredydev.Unisys.COM> paul@tredysvr.Tredydev.Unisys.COM (Paul Siu) writes:
>In ANSI C, you can define a variable as constant by preceeding it with const.
>You can for example define a double variable x that you cannot change by
>
>     const double x;
>
>However, what is the advantage of using const over #define?  Why was the
>reason for its addition to ANSI C.

    Your variable x above is pretty useless, since it has no initialized
value (and is therefore zero).  How about:

const char	*foo	= "some really long string";

    If this is #defined, and is accessed in several places, your
compiler may save multiple copies of the string.  Even if your compiler
is smart enough to make it a single instance, it won't do this over
several modules. 

  Another advantage is in the optimization phases, where the const keyword
provides more information to the optimizer.


-- 
 _
Kevin D. Quitt         demott!kdq   kdq@demott.com
DeMott Electronics Co. 14707 Keswick St.   Van Nuys, CA 91405-1266
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