On Tue, Oct 09, 2007 at 08:33:59PM +0200, Philipp Matthias Hahn wrote:
> 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 static char pointers to error message strings have been replaced by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
Only the pointer can be changed here. AFAIK "a" is a const string.
> const char * b = "b"; // the thing pointed to is const
The "const" here is redundant (just useful for forcing the compiler to
prevent us from shooting our feet). The "b" string is already constant.
> 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';
This will segfault.
> a++;
> *b = 'B'; // error: assignment of read-only location
> b++;
> *c = 'C';
Last line will segfault too.
> c++; // error: increment of read-only variable 'c'
> *d = 'D'; // error: assignment of read-only location
> d++; // error: increment of read-only variable 'd'
> }
>
Please continue below.
> > 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.
>
Got the point, Thanks!.
--
Ahmed S. Darwish
HomePage: http://darwish.07.googlepages.com
Blog: http://darwish-07.blogspot.com
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