Hello
I'm porting some C++ stuff to C and having problem to get it through
gcc.
Here is a condensed version of the problem:
void foo(const int * const * const ptr)
{}
main()
{
int i = 5;
int *ptr = &i;
foo(&ptr);
}
The warning is:
warning: passing arg 1 of `foo' from incompatible pointer type.
Can't C implicit cast a int** to 'const int * const * const'? (it
works fine in C++)
/Jonas
Jun 1 '07
14  2960 
Ben Bacarisse wrote:
<snip>
If it were that simple, then assigning a char * to a const char *
would also be a constraint violation and it is not.
<snip>
That was an excellent clarification, great post Ben!
--
Tor <torust [at] online [dot] no>
CBFalconer wrote:
Tor Rustad wrote:
>CBFalconer wrote:
[...]
>>No. const objects must be initialized at declaration time.
Before posting, I even checked that 'pcpci' was a pointer (to const
pointer to const int).
What am I missing exactly?
You can't write to const objects.
I know that, and didn't do such a thing. :-)
--
Tor <torust [at] online [dot] no>
On Sat, 02 Jun 2007 05:47:06 +0100, Ben Bacarisse
<be********@bsb .me.ukwrote:
<snip: 6.5.16.1>
So assignment (and, by extension, parameter passing) is allowed to "add
qualifiers" to the pointed-to type (but not to the type pointed-to by
the pointed-to type).
As far as I can tell, this rule is somewhat arbitrary and is intended,
presumably, to simplify the compiler's job. It (or something like it)
is required because without it a constraint-free program could modify
a const object[1] but at least one other language took the view that
all "safe" assignments would be allowed. Thus the OP's original
example (with const at every level) causes not a peep from a C++
compiler.
Does anyone know the reason C chose this safe but restrictive rule?
Does it significantly simplify the compiler?
In ~1989 when const was added they chose they simplest rule that was
obviously safe. It may or may not have significantly simplified the
compiler, but it did significantly simplify programmers', and standard
writers' and voters', rapid understanding of this new feature.
With several years of experience, C++ could choose the somewhat more
flexible rule of adding qualification at all or multiple inner levels.
C99 probably could have followed C++(98) but didn't. I don't know if
it was proposed, although they did have plently of other work to do.
- formerly david.thompson1 || achar(64) || worldnet.att.ne t
David Thompson <da************ @verizon.netwri tes:
On Sat, 02 Jun 2007 05:47:06 +0100, Ben Bacarisse
<be********@bsb .me.ukwrote:
<snip: 6.5.16.1>
>So assignment (and, by extension, parameter passing) is allowed to "add
qualifiers" to the pointed-to type (but not to the type pointed-to by
the pointed-to type).
<snip>
>Does anyone know the reason C chose this safe but restrictive rule?
Does it significantly simplify the compiler?
In ~1989 when const was added they chose they simplest rule that was
obviously safe. It may or may not have significantly simplified the
compiler, but it did significantly simplify programmers', and standard
writers' and voters', rapid understanding of this new feature.
Ah, yes. I was ignoring the value a simple rule would have for
understanding and acceptance.
--
Ben.
David Thompson <da************ @verizon.netwro te:
>
C99 probably could have followed C++(98) but didn't. I don't know if
it was proposed, although they did have plently of other work to do.
It was certainly considered, but there are substantial (and sometimes
quite subtle) differences between the way the C and C++ standards
describe their respective languages such that the rules couldn't just be
transplanted intact, but would have to be rewritten. And C99 added the
restrict qualifier that isn't covered by the existing C++ rules and
behaves quite differently from const and volatile. All in all, it would
have been a good bit of work and no one volunteered to undertake it.
I'm reasonably sure the committee would be happy to consider relaxed
conversion rules if someone were to work out the details and propose
them.
-Larry Jones
If I get a bad grade, it'll be YOUR fault for not doing the work for me!
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