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List:       gcc-bugs
Subject:    dynamic_cast bugs
From:       Carlo Wood <carlo () runaway ! xs4all ! nl>
Date:       1999-11-15 13:33:01
[Download RAW message or body]

The following code snippet:

---
#include <iostream>

class V { };

class A : public virtual V { };

class B : public ostream, public A { public: virtual void foo(void) { } };

class C : public istream, public virtual V { };

class D : public B, public C { };

class E : public B, public virtual V { };

int main(void)
{
  D d;
  E e;

  ostream* osd = &d;
  ostream* ose = &e;

  if (dynamic_cast<V*>(osd))
    cout << "D contains V" << endl;
  else
    cout << "D doesn't contain V?!" << endl;

  if (dynamic_cast<V*>(ose))
    cout << "E contains V" << endl;
  else
    cout << "E doesn't contain V?!" << endl;

  return 0;
}
---

Produces with gcc-2.95.1 (release):

~/c++/tests>g++ -save-temps -v -Wall -ansi -pedantic dc.cc
Reading specs from /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/specs
gcc version 2.95.1 19990816/Linux (release)
 /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/cpp -lang-c++ -v -D__GNUC__=2 -D__GNU
G__=2 -D__GNUC_MINOR__=95 -D__cplusplus -trigraphs -D__STRICT_ANSI__ -D__ELF__ -
D__unix__ -D__i386__ -D__linux__ -D__unix -D__linux -Asystem(posix) -D__EXCEPTIO
NS -Wall -pedantic -Acpu(i386) -Amachine(i386) -D__i386 -D__i386__ -D__i686 -D__
i686__ -D__pentiumpro -D__pentiumpro__ dc.cc dc.ii
GNU CPP version 2.95.1 19990816/Linux (release) (i386 Linux/ELF)
#include "..." search starts here:
#include <...> search starts here:
 /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/../../../../include/g++-3
 /usr/local/include
 /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/include
 /usr/include
End of search list.
The following default directories have been omitted from the search path:
 /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/../../../../i686-redhat-linux/include
End of omitted list.
 /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/cc1plus dc.ii -quiet -dumpbase dc.cc 
-Wall -pedantic -ansi -version -o dc.s
GNU C++ version 2.95.1 19990816/Linux (release) (i686-redhat-linux) compiled by 
GNU C version 2.95.1 19990816/Linux (release).
 as -V -Qy -o dc.o dc.s
GNU assembler version 2.9.5 (i686-pc-linux-gnu) using BFD version 2.9.5.0.14
 /usr/lib/gcc-lib/i686-redhat-linux/2.95.1/collect2 -m elf_i386 -dynamic-linker 
/lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o /usr/lib/gcc-lib/i686-redhat-
linux/2.95.1/crtbegin.o -L/usr/lib/gcc-lib/i686-redhat-linux/2.95.1 -L/usr/i686-
redhat-linux/lib dc.o -lstdc++ -lm -lgcc -lc -lgcc /usr/lib/gcc-lib/i686-redhat-
linux/2.95.1/crtend.o /usr/lib/crtn.o

~/c++/tests>grep dynamic dc.s
        call __dynamic_cast
        call __dynamic_cast

~/c++/tests>a.out
D contains V
E doesn't contain V?!

This is, I believe, a bug.  VC++ (on windows) results in:

D contains V
E contains V

which I think is correct.


A later cvs version results in:

~/c++/tests>g++-cvs -save-temps -v -Wall -ansi -pedantic dc.cc
Reading specs from /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/specs
gcc version 2.96 19991102 (experimental)
 /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/cpp -lang-c++ -v -D__GNUC__=2 \
-D__GNUG__=2 -D__GNUC_MINOR__=96 -D__cplusplus -trigraphs -D__STRICT_ANSI__ -D__ELF__ \
-D__unix__ -D__i386__ -D__linux__ -D__unix -D__linux -Asystem(posix) -D__EXCEPTIONS \
-Wall -pedantic -Acpu(i386) -Amachine(i386) -D__i386 -D__i386__ -D__tune_pentiumpro__ \
dc.cc dc.ii GNU CPP version 2.96 19991102 (experimental) (i386 Linux/ELF)
#include "..." search starts here:
#include <...> search starts here:
 /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/../../../../include/g++-3
 /usr/local/egcs/include
 /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/../../../../i686-pc-linux-gnu/include
  /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/include
 /usr/include
End of search list.
The following default directories have been omitted from the search path:
End of omitted list.
 /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/cc1plus dc.ii -quiet -dumpbase \
dc.cc -Wall -pedantic -ansi -version -o dc.s GNU C++ version 2.96 19991102 \
(experimental) (i686-pc-linux-gnu) compiled by GNU C version 2.95.1 19990816/Linux \
(release).  as -V -Qy -o dc.o dc.s
GNU assembler version 2.9.5 (i686-pc-linux-gnu) using BFD version 2.9.5.0.14
 /usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/collect2 -m elf_i386 \
-dynamic-linker /lib/ld-linux.so.2 /usr/lib/crt1.o /usr/lib/crti.o \
/usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/crtbegin.o \
-L/usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96 -L/usr/local/egcs/lib dc.o \
-lstdc++ -lm -lgcc -lc -lgcc \
/usr/local/egcs/lib/gcc-lib/i686-pc-linux-gnu/2.96/crtend.o /usr/lib/crtn.o

~/c++/tests>a.out
a.out: error in loading shared libraries: a.out: undefined symbol: __dynamic_cast_2

~/c++/tests>grep dynamic dc.s
        call    __dynamic_cast_2
        call    __dynamic_cast_2


Regards,
Carlo Wood

PS Could I PLEASE get some feedback on my patch for printing types in
   C++ warnings and errors?  It is still not added to the CVS repository,
   and when I asked for a status in a private mail to one of the maintainers,
   he completely ignored my mail :/ (I feel slightly insulted by such a
   treatment).


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