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From: brnstnd@kramden.acf.nyu.edu (Dan Bernstein)
Newsgroups: comp.lang.c
Subject: Re: When do you use const
Message-ID: <2571:Feb116:51:5891@kramden.acf.nyu.edu>
Date: 1 Feb 91 16:51:58 GMT
References: <1220@tredysvr.Tredydev.Unisys.COM> <1991Feb1.203935.18927@csrd.uiuc.edu>
Organization: IR
Lines: 16

In article <1991Feb1.203935.18927@csrd.uiuc.edu> bliss@sp64.csrd.uiuc.edu (Brian Bliss) writes:
>  func f (const int *x, int *y);
>  then once the comipler fetches the value of *x, it need not fetch
>  it again in the subroutine, means it is constant.  if it were not
>  constant, then we could potentially modify the value of *x by 
>  assigning through *y (if x == y), and the compiler would need to
>  recalculate *x every time it was needed (if *y or any global variable
>  has been modified since the last calculation of *x).

Wait a minute. I thought const was only a prohibitive qualifier (you
can't set *x = foo) rather than an assertive qualifier (*x won't
change while it's in scope). Aren't you allowed to call f(&z,&z) upon an
int z (assuming prototypes are in scope), and doesn't f() have to reload
*x every time?

---Dan