Anyone knows how to write a virtual function for operator<< ?
I have a base class and some public derived class from it.
For the derived class, I hope they can use << to output their
different data. What's more, I want the base class pointers
can access the derived ones and then their corresponding
operator <<. For example:
class base {
// virtual and friend can't be put together, so the following
// code won't work.
virtual friend ostream& operator<< (ostream& os, const base& b);
};
class derived1 : public base
{
virtual friend ostream& operator<< (ostream& os, const base& d1);
};
class derived2 : public base
{
virtual friend ostream& operator<< (ostream& os, const base& d2);
};
I hope they can work like:
base *pb;
derived1 d1;
derived2 d2;
cout<<d1<<"\t"< <d2<<endl; // use their corresponding defination
pb = &d1; // point to class derived1
cout<<*pb<<endl ; // use the operator<< defined in class derived1
pb = &d2; // point to class derived2
cout<<*pb<<endl ; // use the operator<< defined in class derived2
How could I implement the operator overloading then? thanks. 6 7208
On Sat, 10 Apr 2004 21:38:19 -0400 in comp.lang.c++, "Victor"
<la*********@ya hoo.com> wrote, Anyone knows how to write a virtual function for operator<< ?
Public:
virtual ostream & print_on(ostrea m &) const;
} // end class
inline ostream& operator<< (ostream& os, const base& me)
{
return me.print_on(os) ;
}
On Sat, 10 Apr 2004 21:38:19 -0400 in comp.lang.c++, "Victor"
<la*********@ya hoo.com> wrote, Anyone knows how to write a virtual function for operator<< ?
Public:
virtual ostream & print_on(ostrea m &) const;
} // end class
inline ostream& operator<< (ostream& os, const base& me)
{
return me.print_on(os) ;
}
On Sat, 10 Apr 2004 21:38:19 -0400, "Victor" <la*********@ya hoo.com> wrote: Anyone knows how to write a virtual function for operator<< ?
The canonical way to accomplish this is to have a virtual member function
in each class of your heirarchy, say
class base {
public:
virtual ostream &put(ostream &);
// ...
};
class derived : public base {
public:
ostream &put(ostream &);
// ...
};
// etc.
Each implementation of put() simply "puts" *this to the stream, and returns
the stream reference it was passed. Then you'd write a single non-member
(of course) operator<< as follows:
ostream &operator<<(ost ream &os, const base &b)
{
return b.put(os);
}
This will dispatch to the appropriate virtual put() function when called
with any ref to the base or derived class(es) as the 2nd operand.
-leor
--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at: www.bdsoft.com/tools/stlfilt.html
On Sat, 10 Apr 2004 21:38:19 -0400, "Victor" <la*********@ya hoo.com> wrote: Anyone knows how to write a virtual function for operator<< ?
The canonical way to accomplish this is to have a virtual member function
in each class of your heirarchy, say
class base {
public:
virtual ostream &put(ostream &);
// ...
};
class derived : public base {
public:
ostream &put(ostream &);
// ...
};
// etc.
Each implementation of put() simply "puts" *this to the stream, and returns
the stream reference it was passed. Then you'd write a single non-member
(of course) operator<< as follows:
ostream &operator<<(ost ream &os, const base &b)
{
return b.put(os);
}
This will dispatch to the appropriate virtual put() function when called
with any ref to the base or derived class(es) as the 2nd operand.
-leor
--
Leor Zolman --- BD Software --- www.bdsoft.com
On-Site Training in C/C++, Java, Perl and Unix
C++ users: Download BD Software's free STL Error Message Decryptor at: www.bdsoft.com/tools/stlfilt.html
Good idea. It works. Thanks very much
"David Harmon" <so****@netcom. com> wrote in message
news:40******** ******@news.wes t.earthlink.net ... On Sat, 10 Apr 2004 21:38:19 -0400 in comp.lang.c++, "Victor" <la*********@ya hoo.com> wrote,Anyone knows how to write a virtual function for operator<< ?
Public: virtual ostream & print_on(ostrea m &) const; } // end class
inline ostream& operator<< (ostream& os, const base& me) { return me.print_on(os) ; }
Good idea. It works. Thanks very much
"David Harmon" <so****@netcom. com> wrote in message
news:40******** ******@news.wes t.earthlink.net ... On Sat, 10 Apr 2004 21:38:19 -0400 in comp.lang.c++, "Victor" <la*********@ya hoo.com> wrote,Anyone knows how to write a virtual function for operator<< ?
Public: virtual ostream & print_on(ostrea m &) const; } // end class
inline ostream& operator<< (ostream& os, const base& me) { return me.print_on(os) ; } This thread has been closed and replies have been disabled. Please start a new discussion. Similar topics |
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