Hi,
Your code looks suspicious, explained below.
On Wed, 12 Jul 2006, michid@xxxxxxxxx wrote:
> The following program gives different output on g++ 3.3.6 and 4.0.3.
> With 3.3.6 it prints
>
> D::foo()
> D::foo()
>
> with 4.0.3 it prints
>
> C::foo()
> D::foo()
>
> which is what I'd expected it to print. Is this a known issue?
>
> Michael
> #include <iostream>
> using namespace std;
>
> struct B {
> virtual void foo() const = 0;
> };
>
> struct C: B {
> virtual void foo() const { cout << "C::foo()" << endl; }
> };
>
> struct D: B {
> virtual void foo() const { cout << "D::foo()" << endl; }
> };
>
> struct A {
> const B &b;
> A(const B& x = C()): b(x) {}
HERE: parameter x (and member b) are initialized by reference to a
temporary (automatic) object of type C. In other words, it is probably
being destroyed, leaving a dangling reference. Thus, the behavior is
undefined.
> void foo() { b.foo(); }
> };
>
> int main() {
> A a1 = A(C()); // C is dead!
> A a2 = A(D()); // so is D!
> a1.foo();
> a2.foo();
> return 0;
> }
If I had to guess why there are different results:
C and D can either be allocated the same slot on the stack or different,
entirely compiler/optimization dependent.
Fang
