[Bug c++/38484] New: dynamic_cast fails to respect private base when cross casting

[kristian dot spangsege at gmail dot com]

Here is the code:

#include 

struct Reader { virtual ~Reader() {} };
struct Writer: virtual Reader {};

void func(Reader *r)
{
  std::cout << dynamic_cast(r) << std::endl;
}

struct AccessorReader: virtual Reader {};
struct Accessor: AccessorReader, private Writer {};

int main()
{
  Accessor a;
  func(static_cast(&a));
  return 0;
}


What happens is that the dynamic_cast in "func" succeeds to convert the Reader
* to a Writer *. This is unexpected due to the private inheritance of Writer in
Accessor.

If the virtual inheritance of Reader is changed to ordinary inheritance in both
places, the problem goes away, i.e. the dynamic_cast returns 0.

I am not entirely sure this is a bug, but I do know that dynamic_cast is
supposed to respect privacy, and as far as I can see, there is no way, in the
above code, that "func" can know that the Reader is also a Writer without
violating the privacy specification.

I'd be happy if someone could clarify this matter for me.

Version: gcc (GCC) 4.3.0 20080428 (Red Hat 4.3.0-8)


-- 
   Summary: dynamic_cast fails to respect private base when cross
casting
   Product: gcc
   Version: 4.3.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kristian dot spangsege at gmail dot com
 GCC build triplet: x86_64-redhat-linux
  GCC host triplet: x86_64-redhat-linux
GCC target triplet: x86_64-redhat-linux


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38484

[Bug c++/38484] dynamic_cast fails to respect private base when cross casting

[kristian dot spangsege at gmail dot com]

--- Comment #1 from kristian dot spangsege at gmail dot com  2008-12-11 
11:27 ---
Totally BOGUS - sorry!


-- 

kristian dot spangsege at gmail dot com changed:

   What|Removed |Added

 Status|UNCONFIRMED |RESOLVED
 Resolution||INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=38484

[Bug c++/27775] incorrect "ambiguous" error message with multiple inheritance and nested class.

[kristian dot spangsege at gmail dot com]

--- Comment #2 from kristian dot spangsege at gmail dot com  2008-08-10 
09:49 ---
I just confirmed this bug in GCC 4.3.0.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=27775

[Bug c++/34824] New: ICE with explicit copy constructor

[kristian dot spangsege at gmail dot com]

The following small test case causes GCC to ICE:

struct A;

struct B
{
  B(A const &);
  explicit B(B const &);
};

struct A
{
  A(B) {}
};

B f(A const &a) { return B(a); }


Same result (ICE) on the following two systems:

gcc (GCC) 4.1.2 20061115 (prerelease) (Debian 4.1.1-21)
gcc (GCC) 4.1.1 20070105 (Red Hat 4.1.1-51)


If the "explicit" keyword is dropped the ICE disappears. The same is true if
the argument to A's constructor is changed to an reference.


-- 
   Summary: ICE with explicit copy constructor
   Product: gcc
   Version: 4.1.2
Status: UNCONFIRMED
  Severity: normal
  Priority: P3
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: kristian dot spangsege at gmail dot com
 GCC build triplet: 4.1.2
  GCC host triplet: 4.1.2
GCC target triplet: 4.1.2


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34824

[Bug c++/34824] ICE with explicit copy constructor

[kristian dot spangsege at gmail dot com]

--- Comment #1 from kristian dot spangsege at gmail dot com  2008-01-17 
07:37 ---
Just tested it on the latest release 4.2.2 build from source with no patches
and the ICE is still there.

System:
g++ (GCC) 4.2.2
Linux localhost.localdomain 2.6.20-1.2952.fc6 #1 SMP Wed May 16 18:59:18 EDT
2007 i686 i686 i386 GNU/Linux
Fedora Core release 6 (Zod)


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=34824