[Bug libstdc++/20647] Wrong typeid for incomplete types

[frederic dot riss at gmail dot com]

--- Comment #6 from frederic dot riss at gmail dot com  2005-11-06 16:33 
---
I nearly forgot that I submitted this bug report... 
I got myself a version of the C++ standard since I submitted that, and I just
had a look at the part describing typeid :

5.2.8.4 reads : "When typeid is applied to a type-id, [...]. If the type
of the type-id is a class type or a reference to a class type, the class shall
be completely-defined."

I believe A* in 2.C qualifies a a reference to a not-completely defined class
type, and thus shouldn't be passed to std::typeid. 

I'm not an expert in standard reading, but it seems to me that the current
behaviour isn't really a bug. If possible, I would be glad to see a warning
emited by GCC in that case, because I hit that problem in real-world code
(generic callback system using boost::any behind the scenes) and I spent hours
finding out what was happening. Maybe I should suggest adding a concept check
to the boost code if it is possible to detect it.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20647

[Bug libstdc++/20647] Wrong typeid for incomplete types

[frederic dot riss at gmail dot com]

--- Comment #12 from frederic dot riss at gmail dot com  2005-11-06 18:35 
---
When I read the standard, I thought that 'reference to a class type' was used
in a sort of general way covering pointers and C++ references. I interpreted
this that way because I don't see what difference it could make to a compiler
and/or a developper that typeid(A*) is valid while typeid(A&) isn't. 
So just for my personal knowledge, what could be the rationale behind this
special casing ?


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20647

[Bug c++/20647] New: Wrong typeid for incomplete types

[frederic dot riss at gmail dot com]

On linux x86, using the following 2 little sources files :

-- 1.C 
#include 

class A {
public:
A() {}
};

extern void foo(const std::type_info&);

int main()
{
foo(typeid(A*));
return 0;
}
---

-- 2.C 
#include 
#include 

class A;

void foo(const std::type_info& t)
{
if (t == typeid(A*))
{
std::cout << "OK\n";
}
else
{
std::cout << "KO\n";
}
}
---

and compiling with "g++ 1.C 2.C" gives me KO output. This means that the
comparison of the type_info passed to foo and the one computed by typeid(A*)
where A* is an incomplete type failed. 

In the binary there are 2 type_info symbols for A* :
 % nm a.out| grep TIP1A
0804884c r _ZTIP1A
0804882c V _ZTIP1A

I tried this test with many compilers and it worked with g++ 3.2 and failed with
g++ 3.3, 3.4 and pre4.0 (with the same binutils). Precise versions :

 % gcc-3.2 --version
gcc-3.2 (GCC) 3.2.3 (Debian)

 % gcc-3.3 --version
gcc-3.3 (GCC) 3.3.5 (Debian 1:3.3.5-8ubuntu2)

 % gcc-3.4 --version
gcc-3.4 (GCC) 3.4.4 20050209 (prerelease) (Debian 3.4.3-9ubuntu3)

 % gcc-4.0 --version
gcc-4.0 (GCC) 4.0.0 20050301 (prerelease) (Debian 4.0-0pre6ubuntu6)

-- 
   Summary: Wrong typeid for incomplete types
   Product: gcc
   Version: 3.4.0
Status: UNCONFIRMED
  Severity: normal
  Priority: P2
 Component: c++
AssignedTo: unassigned at gcc dot gnu dot org
    ReportedBy: frederic dot riss at gmail dot com
CC: gcc-bugs at gcc dot gnu dot org


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20647

[Bug c++/20647] Wrong typeid for incomplete types

[frederic dot riss at gmail dot com]

--- Additional Comments From frederic dot riss at gmail dot com  2005-04-01 
21:45 ---
Andrew, I don't fully get what you mean and seeing no activity on this bug makes
me wonder if you expect some feedback from me... Experimenting based on your
comment I tried using -fno-weak, but it doesn't work nor seems recommended. So I
wonder if what I see is a real bug, me misusing C++ or maybe a bug in the
packages I use.

-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=20647