From mboxrd@z Thu Jan  1 00:00:00 1970
From: Andreas Schwab <schwab@issan.informatik.uni-dortmund.de>
To: "Han Holl" <jeholl@euronet.nl>
Cc: egcs@cygnus.com
Subject: Re: Don't understand cv-quals message
Date: Mon, 02 Feb 1998 02:38:00 -0000
Message-id: <vyzwwfeuwgi.fsf@issan.informatik.uni-dortmund.de>
References: <19980201122701.23062.qmail@optiplex.palga.uucp>
X-SW-Source: 1998-02/msg00067.html

Han Holl <jeholl@euronet.nl> writes:

|> If I compile the following program (with egcs-1.0.1) :


|> #include <iostream.h>

|> void f(const char** s)
|> {
|> 	cout << *s << endl;
|> }
|> main()
|> {
|> 	char *cs = "abcd";

|> 	f(&cs);
|> }

|> with:
|> g++ --pedantic

|> I get the following warning:

|> t1.C: In function `int main()':
|> t1.C:11: warning: passing `char **' as argument 1 of `f(const char **)' \
|> 			adds cv-quals without intervening `const'

|> What does this mean, and can I do anything to make it go away? (I.e.,
|> can I make this code even more 'pedanticly' correct ? I fail to see how).

Declare cs as const char *, because that is what it really is (since you
are assigning it a constant string).

|> As I understand this, what f() does is promise not to poke around in the 
|> characters, and I should be able to pass a non-const char ** to it.
|> (This works of course with passing char * to a const char * function).

If you change f as follows you'll see the problem:

void f(const char **s)
{
  static const char f_s1[] = "asdf";
  *s = f_s1; // OK
}

main()
{
  static char main_s1[] = "asdf"; // make it writable
  char *cs = main_s1; // OK
  *cs = 'b'; // OK
  f(&cs); // BAD
  *cs = 'b'; // Overwriting constant f_s1!
}

See also the comp.lang.c FAQ.

-- 
Andreas Schwab                                      "And now for something
schwab@issan.informatik.uni-dortmund.de              completely different"
schwab@gnu.org