RE: [Dev-C++] const modifier?

[Juliano <jp...@bo...>]

	Oh God... :). I think its clear now... At least for me. Thank
you.

	Juliano

-----Original Message-----
From: dev...@li...
[mailto:dev...@li...] On Behalf Of Mac
Reiter
Sent: sexta-feira, 14 de junho de 2002 16:55
To: 'Dev-C++ Mailing List'
Subject: RE: [Dev-C++] const modifier?


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- http://dominios.bol.com.br





I must apologize for _part_ of my preceding post, and should remember to
always run programs to make sure I'm not off slightly.  I was still
right about the particular case raised by Juliano:

const char *y  =3D=3D> (const char) (*) y =3D=3D> y is mutable pointer =
to const
char

(mutable just means non-const)  This means that "const char *y" will
allow you to change *where* y points, but will not allow you to change
the data that y is pointing at.


If you read my previous post, you would think that what you want is:

(WARNING : the following decomposition is incorrect!)
char const *y  =3D=3D> (char) (const *) y =3D=3D> y is const pointer to =
mutable
char

However, this is *WRONG*.  "char const *y" is functionally identical to
"const char *y".  (I really hate this syntax...)  I discovered this
while writing a test program.  To make the pointer constant, but the
characters mutable, you need:

char * const y =3D=3D> (char *) (const y) =3D=3D> y is a const pointer =
to
mutable char

(I hate this syntax.  I hate this syntax.  I hate this syntax.)

Apparently C++ parses these two declarations identically:

const char *y  =3D=3D> (const char *) (y)
char const *y  =3D=3D> (char const *) (y)

------------------------------------------------------------------------
-
THE MORAL OF THE STORY:
Split pointer declarations at the '*'.  Then you can tell where the
const will be applied.

const char * y  =3D=3D> (const char) * (y) =3D=3D> chars are const, y is =
mutable
char const * y  =3D=3D> (char const) * (y) =3D=3D> chars are const, y is =
mutable
char * const y  =3D=3D> (char) * (const y) =3D=3D> chars are mutable, y =
is const

const char * const y =3D=3D> (const char) * (const y) =3D=3D>
							 chars are
const, y is const

const char const * const y =3D=3D> (const char const) * (const y) =
=3D=3D>
						warning: const specifier
used twice
------------------------------------------------------------------------
-

Here is the test code -- put it in a file and compile it.  The compiler
will throw an error on the two lines where a constant value is being
changed (or trying to be changed...)


int main(int argc, char **argv)
{
        char buffer1[] =3D "Hello";
        char buffer2[] =3D "World";

	  // This declares a mutable pointer that points to constant
data
        const char * a =3D &(buffer1[0]);

        // This declares a constant pointer that points to mutable data
        char * const b =3D &(buffer1[0]);

        a[1] =3D 'u'; // illegal, because "mutable a" points to "const
char"
        b[1] =3D 'u'; // OK, because "const b" is a mutable "char *"

        a =3D &(buffer2[0]); // OK, because "mutable a" can change
        b =3D &(buffer2[0]); // illegal, because "const b" cannot change =
}


Anybody care to join me in my mantra?

I HATE THIS SYNTAX!
I Hate This Syntax!
i hate this syntax
...
..
.

Mac


At 04:10 PM 6/14/02 -0300, Juliano wrote:
>	I'm sorry if I'm wrong, but... Isn't "const char *y" a way to
say that=20
>the address value stored in the pointer "y" can't be changed? In other=20
>words, I can change the value pointed by the address stored in "y", but

>I can't change the address stored in "y" itself.
>
>	Isn't it the way pointers work? Am I doing something wrong?
>
>	[]s
>	Juliano

[My previous post clipped out because it contained incorrect
information, which I choose not to propagate any further...  Mac]
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