[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #10 from m-matti-a dot lehtonen at iki dot fi 2007-11-20 21:53
---
This code piece cannot compiled without warnings or errors.
/*! Presentation of transformation matrix */
typedef coordinate_ttransform_matrix_t[ 4 ][ 4 ];
...
void
transform_concat
(
transform_matrix_ttransform,
transform_matrix_t const transform1,
transform_matrix_t const transform2
);
...
void
transform_rotate
(
transform_matrix_ttransform,
real_t const angles[ 3 ]
)
{
transform_matrix_t
temp;
...
transform_concat( transform, transform, temp );
...
}
Without casts I got two warnings:
warning: passing argument 2 of #8216;transform_concat#8217; from incompatible
pointer type
warning: passing argument 3 of #8216;transform_concat#8217; from incompatible
pointer type
And if arument 2 and 3 are casted as
transform_concat( transform, (const transform_matrix_t) transform, (const
transform_matrix_t) temp );
Then I got two errors:
error: cast specifies array type
error: cast specifies array type
--
m-matti-a dot lehtonen at iki dot fi changed:
What|Removed |Added
CC||m-matti-a dot lehtonen at
||iki dot fi
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #6 from jozef dot behran at krs dot sk 2007-09-26 12:06 --- Neither C nor C++ have qualified array types, only arrays of qualified element types, but C++ has different rules from C regarding conversions involving qualifiers, which allow some conversions (involving arrays or pointers to pointers) not allowed in C. Could you give me reference in the C standard where this is stated ? The section 6.7.3, paragraph 8, says nothing about C/C++ not having qualified array types, it only says that a qualifier applied to an array type holds for the element type of the array type (these two are not the same things, see bug 16602 for more discussion about the topic). -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #7 from jozef dot behran at krs dot sk 2007-09-26 12:18 --- Neither C nor C++ have qualified array types, only arrays of qualified element types, but C++ has different rules from C regarding conversions involving qualifiers, which allow some conversions (involving arrays or pointers to pointers) not allowed in C. And another point: Whether C/C++ have or don't have qualified array types, still the difference between the const caca * and caca * types is a const qualifier being applied to some part of the caca * base type. Therefore the types must be compatible when the automatic type conversion involved only adds const qualifiers to the type. Therefore the warnings are not legitimate. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #8 from joseph at codesourcery dot com 2007-09-26 12:38 --- Subject: Re: Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one On Wed, 26 Sep 2007, jozef dot behran at krs dot sk wrote: Could you give me reference in the C standard where this is stated ? The section 6.7.3, paragraph 8, says nothing about C/C++ not having qualified array types, it only says that a qualifier applied to an array type holds for the element type of the array type (these two are not the same things, see bug 16602 for more discussion about the topic). That which you quote means there is no way to put a qualifier on the array type because any attempt to do so puts it on the element type instead. That there are no qualified array types is simply the logical conclusion from there being no C syntax to write one. Note not the array type in that paragraph. The question of whether abstractly one might imagine a qualified array type in C despite the lack of syntax to describe one, and how such a type (notwithstanding the lack of syntax to describe it) would behave if it were to exist, is not an interesting one in the absence of implementation extensions to define such a type. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #9 from joseph at codesourcery dot com 2007-09-26 12:42 --- Subject: Re: Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one On Wed, 26 Sep 2007, jozef dot behran at krs dot sk wrote: And another point: Whether C/C++ have or don't have qualified array types, still the difference between the const caca * and caca * types is a const qualifier being applied to some part of the caca * base type. Therefore the types must be compatible when the automatic type conversion involved only adds const qualifiers to the type. Therefore the warnings are not legitimate. Read the C FAQ. You can't pass a char ** where a const char ** is expected either in C. That's how the language works. http://c-faq.com/ansi/constmismatch.html C++ allows certain cases C doesn't that can be shown to be safe, as noted in that FAQ. A proposal to make C use the C++ rules was rejected in the course of C99 development. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #3 from jbeulich at novell dot com 2007-09-19 09:39 --- Isn't this the same as 16602 (which I don't really understand why it was rejected as invalid)? Also, if this *is* invalid, then what proper mechanism does one have to express what is intended here? And why does similar code compile warning free in C++? -- jbeulich at novell dot com changed: What|Removed |Added CC||jbeulich at novell dot com http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #4 from schwab at suse dot de 2007-09-19 09:47 --- *** This bug has been marked as a duplicate of 16602 *** -- schwab at suse dot de changed: What|Removed |Added Status|UNCONFIRMED |RESOLVED Resolution||DUPLICATE http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #5 from joseph at codesourcery dot com 2007-09-19 19:54 --- Subject: Re: Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one On Wed, 19 Sep 2007, jbeulich at novell dot com wrote: Isn't this the same as 16602 (which I don't really understand why it was rejected as invalid)? Also, if this *is* invalid, then what proper mechanism does one have to express what is intended here? And why does similar code compile warning free in C++? Neither C nor C++ have qualified array types, only arrays of qualified element types, but C++ has different rules from C regarding conversions involving qualifiers, which allow some conversions (involving arrays or pointers to pointers) not allowed in C. -- http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #1 from raeburn at raeburn dot org 2007-08-15 06:13 ---
Subject: Re: New: Warning when passing a pointer to a const array to a
function that expects a pointer to a non-cast one
On Aug 14, 2007, at 23:45, martin dot ferrari at gmail dot com wrote:
Sorry if I'm misunderstanding something or this is a FAQ, but I
couldn't find
any reference, except for a unanswered mail with the same problem
from 2000 at
http://gcc.gnu.org/ml/gcc-bugs/2000-10/msg00337.html (and I don't
find it in
bugzilla either). The code looks semantically correct to me, the
function
declares that it won't touch the data and I'm passing a non-const
data. If the
typecast is not to an array, the warning goes away.
/home/martin/test.c:8: warning: passing argument 1 of foo from
incompatible
pointer type
typedef int caca[3];
void foo (const caca* p);
void bar(caca *c) {
foo(c);
}
I think this might be related to the bug report I filed in 31887 --
and I'm starting to think that we might both be wrong.
Weird as it seems, my reading of the C spec, section 6.7.3 says that
the qualifier (const, in both our cases, but it would apply to
volatile as well) applies only to the array element type, and does
*not* apply to the array type itself. So this isn't like assigning a
char * value to a const char *; you're dealing with pointers to
two different array types (which happen to have similar but
differently-qualified element types).
I'm not 100% sure I believe this interpretation, because it seems to
needlessly prohibit perfectly reasonable code, and when I asked on
comp.std.c a couple weeks back, I got some mixed feedback. But at
the moment, that's my reading of the spec
Ken
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
[Bug c/33076] Warning when passing a pointer to a const array to a function that expects a pointer to a non-cast one
--- Comment #2 from raeburn at raeburn dot org 2007-08-15 06:15 ---
Subject: Re: New: Warning when passing a pointer to a const array to a
function that expects a pointer to a non-cast one
On Aug 14, 2007, at 23:45, martin dot ferrari at gmail dot com wrote:
Sorry if I'm misunderstanding something or this is a FAQ, but I
couldn't find
any reference, except for a unanswered mail with the same problem
from 2000 at
http://gcc.gnu.org/ml/gcc-bugs/2000-10/msg00337.html (and I don't
find it in
bugzilla either). The code looks semantically correct to me, the
function
declares that it won't touch the data and I'm passing a non-const
data. If the
typecast is not to an array, the warning goes away.
/home/martin/test.c:8: warning: passing argument 1 of foo from
incompatible
pointer type
typedef int caca[3];
void foo (const caca* p);
void bar(caca *c) {
foo(c);
}
I think this might be related to the bug report I filed in 31887 --
and I'm starting to think that we might both be wrong.
Weird as it seems, my reading of the C spec, section 6.7.3 says that
the qualifier (const, in both our cases, but it would apply to
volatile as well) applies only to the array element type, and does
*not* apply to the array type itself. So this isn't like assigning a
char * value to a const char *; you're dealing with pointers to
two different array types (which happen to have similar but
differently-qualified element types).
I'm not 100% sure I believe this interpretation, because it seems to
needlessly prohibit perfectly reasonable code, and when I asked on
comp.std.c a couple weeks back, I got some mixed feedback. But at
the moment, that's my reading of the spec
Ken
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=33076
