linux-kernel - Re: [PATCH] NTFS error messages: replace static char pointers by static char arrays

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Message-ID: <20071009183359.GB3945@titan.lahn.de>
Date:	Tue, 9 Oct 2007 20:33:59 +0200
From:	Philipp Matthias Hahn <pmhahn@...an.lahn.de>
To:	"Ahmed S. Darwish" <darwish.07@...il.com>
Cc:	Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] NTFS error messages: replace static char pointers by
	static char arrays

Hello!

On Tue, Oct 09, 2007 at 02:40:35PM +0200, Ahmed S. Darwish wrote:
> On Tue, Oct 09, 2007 at 01:55:42AM +0400, Dmitri Vorobiev wrote:
> > The patch below contains a small code clean-up for the NTFS driver: all
> > static char pointers to error message strings have been replaced by 
> > static char arrays.

      char *       a = "a"; // pointer and content can be changed
const char *       b = "b"; // the thing pointed to is const
      char * const c = "c"; // the pointer is const
const char * const d = "d"; // pointer and content can't be changed

void foo(void) {
        *a = 'A';
        a++;
        *b = 'B'; // error: assignment of read-only location
        b++;
        *c = 'C';
        c++;      // error: increment  of read-only variable 'c'
        *d = 'D'; // error: assignment of read-only location
        d++;      // error: increment  of read-only variable 'd'
}

> Isn't the only difference between char *c = "msg" and char c[] = "msg" is 
> that the first is a non-const pointer to a const char array while the second 
> is a modifiable char array ?

$ cat [ab].c
const char *a = "a";
const char b[] = "b";
$ gcc -c [ab].c
$ size [ab].o
   text    data     bss     dec     hex filename
      2       4       0       6       6 a.o
      2       0       0       2       2 b.o

'a' has two entries: one for the named read-writeable pointer, and one for the
    anonymous read-only string, the pointer points to.
'b' has a single entry: just the named read-only string.

BYtE
Philipp
-- 
  / /  (_)__  __ ____  __ Philipp Hahn
 / /__/ / _ \/ // /\ \/ /
/____/_/_//_/\_,_/ /_/\_\ pmhahn@...an.lahn.de
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