double pointers

[junky_fellow]

Do all double pointers have same size on a particular implementation.

eg char **c_ptr;
int **i_ptr;

Is the size of c_ptr and i_ptr always same (on same implementation)
or it may be different ?

[Robert Gamble]

CBFalconer wrote:

Robert Gamble wrote:

CBFalconer wrote:

Ravi Uday wrote:
S.Tobias wrote:

... snip ...

> Apart of that, pointers to structs, unions and un/qualified
> compatible types have to have the same representation (and
> size) within their respective group.

couldnt get that. Do you mean sizeof (struct *a) == sizeof
(union *b) etc !

Yes. This is needed so self-referencing structures can be created,
as in:

struct blah {
struct blah *next;
whatever info;
}

because the need for struct blah * size arises before struct blah
has been defined.

I not making the connection here. Why does this require that
sizeof(struct *a) == sizeof(union *b) and from where in the Standard
to you conclude that this statement is guaranteed to be true?

Because, to saw off enough space to hold a struct blah, you have to
know how much room a struct blah * takes (with the above
definition). Thus the size and alignment of a struct blah * cannot
depend on the size of a struct blah.

What does this have to do with unions though?

Robert Gamble

[Keith Thompson]

CBFalconer <cb********@yah oo.com> writes:

Robert Gamble wrote:

[...]

I not making the connection here. Why does this require that
sizeof(struct *a) == sizeof(union *b) and from where in the Standard
to you conclude that this statement is guaranteed to be true?

Because, to saw off enough space to hold a struct blah, you have to
know how much room a struct blah * takes (with the above
definition). Thus the size and alignment of a struct blah * cannot
depend on the size of a struct blah.

That implies that all struct pointers have to be the same size, and
that all union pointers have to be the same size. It doesn't imply
that struct pointers have to be the same size as union pointers
(though I'd bet they are on everything other than the DS9K).

--
Keith Thompson (The_Other_Keit h) ks***@mib.org <http://www.ghoti.net/~kst>
San Diego Supercomputer Center <*> <http://users.sdsc.edu/~kst>
We must do something. This is something. Therefore, we must do this.