C++ calling completely wrong (virtual) method of an object

Question

I have some C++ code (written by someone else) which appears to be calling the wrong function. Here\'s the situation:

UTF8InputStreamFromBuffer* cstream = foo();         


        

Answer 1

I would try removing the C-cast first.

• It is completely unnecessary, casts from a Derived to a Base is natural in the language
• It may, actually, cause a bug (though it's not supposed to)

It looks like a compiler bug... it would certainly not be the first either in VS.

I unfortunately don't have VS 2008 at hand, in gcc the casts occur correctly:

struct Base1
{
  virtual void foo() {}
};

struct Base2
{
  virtual void bar() {}
};

struct Derived: Base1, Base2
{
};

int main(int argc, char* argv[])
{
  Derived d;
  Base1* b1 = (Base1*) &d;
  Base2* b2 = (Base2*) &d;

  std::cout << "Derived: " << &d << ", Base1: " << b1
                                 << ", Base2: " << b2 << "\n";

  return 0;
}


> Derived: 0x7ffff1377e00, Base1: 0x7ffff1377e00, Base2: 0x7ffff1377e08