Re: A problem about virtual function?
On Oct 16, 4:42 pm, Erik Wikstr=F6m <Erik-wikst...@telia.com> wrote:
On 2007-10-16 16:09, Wayne Shu wrote:
Today I meet a problem about virtual function. Consider the
following little program.
#include <iostream>
class base
{
int i;
public:
virtual void print() { std::cout << "base" << std::endl; }
virtual ~base() {}
};
class derived : public base
{
public:
virtual void print() { std::cout << "derived" << std::endl; }
};
int main()
{
base b;
b::~base();
new (&b) derived;
(&b)->print(); // (1)
base *p = &b;
p->print();
return 0;
}
I have try the VC2005 Express Edition and GCC 3.4.2
and the result is :
base
derived
Why (1) statement print "base"?
First, I am not sure if it is legal to call the destructor of
an automatic object and then construct a new object of a type
derived from the first object's type in the same place, it
seems very suspect to me.
I think it's undefined behavior; if it isn't, it should be. (To
start with, there's no guarantee that sizeof(derived) <=
sizeof(base).)
--
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