undefined reference, but I think I already defined them

fsshl · 07-15-2011, 05:42 PM

Dear Advanced c/g++ programers:

I tested a simple program about Creating an interface with an Abstract Base Class. from book (C++ cookbook) page 308, 309. Example 8-11. using a pure interface.
----------------------
// Example 8-11 Using a pure interface
class Person {
public:
virtual void eat() = 0;
virtual void sleep() = 0;
virtual void walk() = 0;
virtual void jump() = 0;
};

class IAirbone {
public:
virtual void fly() = 0;
virtual void up() = 0;
virtual void down() = 0;
};

class Superhero : public Person, // A superhero *is* a person
public IAirbone { // and flies
public:
virtual void eat();
virtual void sleep();
virtual void walk();
virtual void jump();
virtual void fly();
virtual void up();
virtual void down();
virtual ~Superhero();
};

void Superhero::walk() {
// ...
}

void Superhero::fly() {
// ...
}

// Implement all of the pure virtuals in Superhero's Superclasses...

int main() {

Superhero superman;
superman.walk(); // Superman can walk like a person
superman.fly(); // or fly like a bird
}
---------------------------------------------------
my g++ 4.5.2 (on linux2.6.35-25) response by
-------------------------------------
eric@eric-laptop:~/cppcookbook/ch8$ g++ Example8-11.cpp
/tmp/ccT3nO5t.o: In function `main':
Example8-11.cpp

.text+0x47): undefined reference to `Superhero::~Superhero()'
/tmp/ccT3nO5t.o: In function `Superhero::Superhero()':
Example8-11.cpp

.text._ZN9SuperheroC2Ev[_ZN9SuperheroC5Ev]+0x24): undefined reference to `vtable for Superhero'
Example8-11.cpp

.text._ZN9SuperheroC2Ev[_ZN9SuperheroC5Ev]+0x2e): undefined reference to `vtable for Superhero'
collect2: ld returned 1 exit status
--------------------------------------------------
actually that book even did not specially define Superhero::walk(), that is
I add by myself to escape my compile's error(is that right? or book's is right?)
you can download the source code of that book's example and test by yourself
http://examples.oreilly.com/9780596007614/
according to book, thses code are compile good in visual c++ 7.1 on window xp
thanks your help a lot in advance, Eric

dwhitney67 · 07-15-2011, 06:15 PM

I assume the following comment means that you implemented all of the remaining virtual methods:

Code:

// Implement all of the pure virtuals in Superhero's Superclasses...

Do not forget to declare your destructor as a 'virtual' method too; and of course, implement it. That's what this error is telling you:

Code:

Example8-11.cpp.text+0x47): undefined reference to `Superhero::~Superhero()'

ta0kira · 07-15-2011, 06:30 PM

You should also make Person::~Person() and IAirborne::~IAirborne() virtual with empty ({}) function bodies. This will give you proper behavior if you want to delete a Person* or an IAirborne*; they will always have a different underlying type if non-NULL, and making the destructors virtual will call the destructor of the most-derived class.
Kevin Barry

fsshl · 07-15-2011, 06:45 PM

thanks your hint
but I am not smart enough to figure out how to fix by your English only explanation.
would you please show out the code?

ta0kira · 07-15-2011, 07:02 PM

"Bad" example:

Code:

#include <iostream>

struct base
{
  virtual void something() = 0;
};

struct derived : public base
{
  void something() { std::cout << "something\n"; }
  ~derived() { std::cout << "good\n"; }
};

int main()
{
  base *pointer = new derived;
  pointer->something();
  delete pointer;
}

"Good" example:

Code:

#include <iostream>

struct base
{
  virtual void something() = 0;
  virtual ~base() {}
};

struct derived : public base
{
  void something() { std::cout << "something\n"; }
  ~derived() { std::cout << "good\n"; }
};

int main()
{
  base *pointer = new derived;
  pointer->something();
  delete pointer;
}

Run both and see what the difference is.
Kevin Barry

fsshl · 07-15-2011, 10:35 PM

Do not forget to declare your destructor as a 'virtual' method too; and of course, implement it. That's what this error is telling you:

I won't forget until someone tell me how to fix it by real code