Re: polymorphism with reference and pointer object

From:
"josh" <xdevel1999@gmail.com>
Newsgroups:
comp.lang.c++
Date:
6 Apr 2007 03:02:14 -0700
Message-ID:
<1175853734.270907.140800@e65g2000hsc.googlegroups.com>
On 6 Apr, 11:37, "Jim Langston" <tazmas...@rocketmail.com> wrote:

"josh" <xdevel1...@gmail.com> wrote in message

news:1175851680.711150.162570@n76g2000hsh.googlegroups.com...

Hi I noticed that when I make a function with a base class parameter
that is a reference
than at run-time the compiler calls a base class function also if I
have passed a derived object.

But if I make that function with a pointer to a base class and then I
pass the derived class
at run-time the compiler calls a derived class function thanks to
dynamic binding.

Now why this difference if a reference is like a pointer and it
contains also an address of????

Thanks!

How is hard to learn C++ ........................


Plese explain. The output of the following program for me is:
Derived
Derived
Derived

What is the output for you?

#include <iostream>
#include <string>

class Base
{
public:
    virtual ~Base() {}
    virtual void Foo() { std::cout << "Base\n"; }

};

class Derived : public Base
{
public:
    virtual void Foo() { std::cout << "Derived\n"; }

};

void Foo( Base* b )
{
    b->Foo();

}

void Bar( Base& b )
{
    b.Foo();

}

int main()
{

    Derived* dp = new Derived();
    Derived d;

    Foo( dp );
    Foo( &d );
// Bar( dp ); // Won't Compile
    // error C2664: 'Bar' : cannot convert parameter 1 from 'Derived *' to
'Base &'
    Bar( d );

    std::string wait;
    std::getline( std::cin, wait );

}


Damn! in my code I have two friend functions with overloaded operators
<<
in which I have a derived class parameter. Than I make
out << static_cast<Base Class>(parameter) and than is called the <<
base class
operator. I have forgotten that friend functions cannot be virtual!

Excuse me!

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