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From:  <yen-kwoon.hun@iugome.com>
To: gcc-bugs@gcc.gnu.org
Subject: sizeof() bug with gcc version 3.4.5 (mingw-vista special r3)
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class base=0D
{=0D
public:=0D
base(){};=0D
~base(){};=0D
};=0D
=0D
class data : public base=0D
{=0D
public:=0D
data(){};=0D
~data(){};=0D
=0D
private:=0D
int member;=0D
}__attribute__((__packed__));=0D
=0D
class group : public base=0D
{=0D
public:=0D
group(){};=0D
~group(){};=0D
=0D
private:=0D
data d1;=0D
data d2;=0D
data d3;=0D
} __attribute__((__packed__));=0D
=0D
int main(int argc, char **argv)=0D
{=0D
std::cout << "base =3D " << sizeof(base) << std::endl;=0D
std::cout << "data =3D " << sizeof(data) << std::endl;=0D
std::cout << "group =3D " << sizeof(group) << std::endl;=0D
return (0);=0D
}=0D
=0D
=0D
The output of the program is:=0D
base =3D 1=0D
data =3D 4=0D
group =3D 13=0D
=0D
The result of sizeof(group) is puzzling as it should be 12 if EBO (empty ba=
se=0D
optimization) worked for both class data and group. Apparently EBO kicked i=
n for=0D
_ONLY_ one of them. If EBO didn't work at all, sizeof(group) should be 16.=
=0D
=0D
Removing the extension of class base from either class group or data will c=
ause=0D
sizeof(group) to return 12. It seems that gcc is unable to fully apply EBO =
when a=0D
class and its member inherits the same empty base class.=0D
=0D
The same code had been tested on microsoft msvc compiler and realview arm=0D
compiler, both correctly optimizes the code and give the correct value as 1=
2.=0D
=0D
Is this a known bug with gcc 3.4.5? I dug through the bugbase but couldn't =
come=0D
up with anything. Maybe EBO isn't the problem at all.=0D
=0D
Thanks!=0D
=0D
=0D
=0D
=0D