Re: string variables and literals

[Joern Rennecke <amylaar at cygnus dot co dot uk>]

> sidster wrote:
> 
> > When you have code like:
> > 
> >    char* p = "some string";
> > 
> > 'p' is a pointer to a constant static string.  The memory location
> > pointed to by 'p' should not be modifiable.
> 
> I'll try to clarify.  This is a string literal: "string literal".  This
> is a pointer to an array of constant characters: const char* cs.  This
> is a pointer to an array of non-constant characters: char* s.  Except
> when initialized with a string literal?  C'mon.
> 
> p is NOT a pointer to a constant static string.  p is a pointer to an
> array of non-constant characters.  You DON'T get a warning when it is
> initialized and you DON'T get a warning when you pass it to a function
> as a char* such as strcmp.  (Well, unless the warning is explictly
> specified.)  But you do get a core dump.  That's not good behavior IMHO.
> 
> > The compiler doesn't warn about this but the user should be smart enough
> > to realize s/he can't modify the character array pointed to by 'p'.
> 
> The compiler should at a minimum issue a warning: "assigning constant
> literal to non-constant variable".  Personally, I would like to see it
> initialize char* variables just as it does char[] variables.  The
> semantics would be more consistent.

That is nonsese, sinze a char* is a pointer, but char[] is an array.

But you can request gcc to allocate string literals non-shared in data
memory with -fwritable-strings, to accomodate broken legacy programs.

> Also, I checked the standard.  Modification of variables declared with
> type char* that are intialized with string literals is undefined.  So
> technically, gcc is standardized in this respect.  But I think gcc
> should ditch the exception that char* variables can be modified UNLESS
> they are initialized with string literals.

You can modify char* variables no matter how they are initialized.
But that is a topic for comp.lang.c