g++ 2.95.1/2 inheritance bug

[Karsten Otto <Karsten dot Otto at xtradyne dot de>]

Hello,

I am currently using g++ version 2.95.1/2 on SuSE Linux 6.2 (2.2.10 kernel).

It seems to compile the following code incorrectly (stream_test.ii):


# 1 "stream_test.cc"
class myinsuper
{
    public:

    virtual myinsuper& operator>>(bool &b) = 0;
    virtual myinsuper& operator>>(myinsuper& (*f)(myinsuper*)) { return f(this); }
};

class myinstream : public myinsuper
{
    public:

    myinstream() : myinsuper() {}

    virtual myinsuper& operator>>(bool &b)
    {
        return *this;
    }
};

myinsuper& op(myinsuper *s)
{
    return *s;
}

int main(int argc, char **argv)
{
    myinstream inp;

    inp >> op;
}


Compilation results in the following error messages:

$ g++ -v --save-temps -c stream_test.cc
Reading specs from /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/specs
gcc version 2.95.1 19990816 (release)
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/cpp -lang-c++ -v -D__GNUC__=2 -D__GNUG__=2 -D__GNUC_MINOR__=95 -D__cplusplus -D__ELF__ -Dunix -D__i386__ -Dlinux -D__ELF__ -D__unix__ -D__i386__ -D__linux__ -D__unix -D__linux -Asystem(posix) -D__EXCEPTIONS -Acpu(i386) -Amachine(i386) -Di386 -D__i386 -D__i386__ -Di586 -Dpentium -D__i586 -D__i586__ -D__pentium -D__pentium__ stream_test.cc stream_test.ii
GNU CPP version 2.95.1 19990816 (release) (i386 Linux/ELF)
#include "..." search starts here:
#include <...> search starts here:
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/../../../../include/g++-3
 /usr/local/include
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/../../../../i586-pc-linux-gnu/include
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/include
 /usr/include
End of search list.
The following default directories have been omitted from the search path:
End of omitted list.
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/cc1plus stream_test.ii -quiet -dumpbase stream_test.cc -version -o stream_test.s
GNU C++ version 2.95.1 19990816 (release) (i586-pc-linux-gnu) compiled by GNU C version 2.95.1 19990816 (release).
stream_test.cc: In function `int main(int, char **)':
stream_test.cc:32: initializing non-const `bool &' with `myinsuper & (*)(myinsuper *)' will use a temporary
stream_test.cc:16: in passing argument 1 of `myinstream::operator >>(bool &)'


Funnily enough, there is a different error message when I use -pedantic:

$ g++ -v --save-temps -pedantic -c stream_test.cc
Reading specs from /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/specs
gcc version 2.95.1 19990816 (release)
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/cpp -lang-c++ -v -D__GNUC__=2 -D__GNUG__=2 -D__GNUC_MINOR__=95 -D__cplusplus -D__ELF__ -Dunix -D__i386__ -Dlinux -D__ELF__ -D__unix__ -D__i386__ -D__linux__ -D__unix -D__linux -Asystem(posix) -D__EXCEPTIONS -pedantic -Acpu(i386) -Amachine(i386) -Di386 -D__i386 -D__i386__ -Di586 -Dpentium -D__i586 -D__i586__ -D__pentium -D__pentium__ stream_test.cc stream_test.ii
GNU CPP version 2.95.1 19990816 (release) (i386 Linux/ELF)
#include "..." search starts here:
#include <...> search starts here:
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/../../../../include/g++-3
 /usr/local/include
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/../../../../i586-pc-linux-gnu/include
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/include
 /usr/include
End of search list.
The following default directories have been omitted from the search path:
End of omitted list.
 /net/linux/egcs/lib/gcc-lib/i586-pc-linux-gnu/2.95.1/cc1plus stream_test.ii -quiet -dumpbase stream_test.cc -pedantic -version -o stream_test.s
GNU C++ version 2.95.1 19990816 (release) (i586-pc-linux-gnu) compiled by GNU C version 2.95.1 19990816 (release).
stream_test.cc: In function `int main(int, char **)':
stream_test.cc:32: no match for `myinstream & >> myinsuper & (&)(myinsuper *)'
stream_test.cc:16: candidates are: class myinsuper & myinstream::operator >>(bool &) <near match>


Obviously, the operator>> taking the function pointer argument is not properly
inherited from class myinsuper to class myinstream. When I copy the definition
line from class myinsuper to class myinstream, the code is compiled correctly.

I also tried changing the line in main() from  inp >> op;  to  inp >> &op;
(which should be equivalent), then the error stated matches the definition
of function op:
stream_test.cc: In function `int main(int, char **)':
stream_test.cc:32: no match for `myinstream & >> myinsuper & (*)(myinsuper *)'
stream_test.cc:16: candidates are: class myinsuper & myinstream::operator >>(bool &) <near match>

I also tried compilation with the newer g++ 2.95.2, but it results in the same
error messages.

Sincerely,

Karsten Otto (kao@xtradyne.de)