invoke sub-class's derived virtual method.

[sam++]

Hi,

I created a pure virtual class P and its derived sub-class D.
In class P, declared a pure virtural function pure(); in sub-class D
define its implementation.

eg.

class P
{
public:
P(P *p) { cout << p->pure(); }
virtual pure() = 0;
~virtual P() {}
}

class D: public P
{
public:
D():P(this) {}
pure() { cout << "derived method is called\n";
~D() {}
}

int main()
{
D *d = new D();
}

I would expect after compiled this program, it will print out the
following result:
"derived method is called"

But it tried to invoke the pure virtual function.
How can I correct this error? For some reason, I don't want to call
d->pure() in the main() function.

Thanks
Sam

[sam++]

sam++ wrote:

Hi,

I created a pure virtual class P and its derived sub-class D.
In class P, declared a pure virtural function pure(); in sub-class D
define its implementation.

eg.

class P
{
public:
P(P *p) { cout << p->pure(); }
virtual pure() = 0;
~virtual P() {}
}

class D: public P
{
public:
D():P(this) {}
pure() { cout << "derived method is called\n";
~D() {}
}

int main()
{
D *d = new D();
}

I would expect after compiled this program, it will print out the
following result:
"derived method is called"

But it tried to invoke the pure virtual function.
How can I correct this error? For some reason, I don't want to call
d->pure() in the main() function.

Thanks
Sam

Sorry, I just some syntax error. Please see the fixed version of the
above example. Just copy to your system and compile it with g++. The
program will invoke the pure virtual function, hence caused core dump.

#include <iostream>
#include <iostream>
#include <fstream>
#include <iomanip>

using namespace std;

class P
{
public:
P(P *p) { p->pure(); }
virtual int pure() = 0;
virtual ~P() {}
};

class D: public P
{
public:
D():P(this) {}
int pure() { cout << "derived method is called\n"; }
~D() {}
};

int main()
{
D *d = new D();
delete d;
}

[John Carson]

http://www.parashift.com/c++-faq-lit....html#faq-10.7
--
John Carson