Basic Animal Inheritence Example

[safe rapids]

I'm trying to make a Animal class hierarchy but I'm getting this error: undefined reference to `vtable for animals::Chicken'

Here is the code:
animals.h

namespace animals {

class Animal {

public:
  virtual void make_noise() = 0;
  virtual void eat() = 0;
  virtual ~Animal() {}
};

class Chicken : public Animal {

  int age;
  bool rooster;

public:
  Chicken() : age(0), rooster(false) {}
  ~Chicken() override {}

  void make_noise() override;

  void eat() override;
};

} // namespace animals

animals.cpp

#include "animals.h"
#include <iostream>

void animals::Animal::make_noise() { std::cout << "be caw!" << '\n'; }
void animals::Animal::eat() { std::cout << "peck... peck.." << '\n'; }

and main.cpp

#include "animals.h"
#include <iostream>

int main() {

  std::cout << "Welcome to C++" << '\n';

  animals::Animal *an = new animals::Chicken();

  an->make_noise();

  return 0;
}

[peak blaze]

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[safe rapids]

CMakeLists.txt ```cmake

...

project(app)

add_executable(app src/main.cpp src/animals.h src/animals.cpp)

set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror")
set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -fsanitize=address --pedantic")

...

[fresh marten]

you probably meant to write animals::Chicken::make_noise() instead of animals::Animal::make_noise(), and same for eat

[safe rapids]

wow...

yes I did lol

thanks

[long mantle]

wait, does that not generate a compiler error?

[fresh marten]

np, stuff like that happens

you can provide an implementation for a pure virtual member function

[proper mauve]

consider a pure virtual destructor, you will almost certainly need to provide a definition

[viral forge]

virtual void make_noise() = 0; and is also defined?

how is that a thing

[long mantle]

I'd consider destructors somewhat separate

[proper mauve]

it will just use the definition when you directly call it

[proper mauve]

destructors are just functions

just special ones

[long mantle]

I mean.... constructors and destructors are kinda special

[fresh marten]

btw, unrelated point: I know it's an example, but don't just new a raw pointer like this. You should use a std::unique_ptr instead so that you're not leaking memory

[proper mauve]

or just declare it locally here

no need to allocate

[safe rapids]

Yes, I'm just learning that. I was going to make it more complete after I figured this out

[viral forge]

isnt pure virtual funcion to prevent instanciating an object of such type? like java abstract

[long mantle]

yes

[viral forge]

so how are you going to call any Animal member function if you can not instantiate an Animal?

[long mantle]

you can call it from a derived class or another memeber function of Animal

[viral forge]

ah directly on the derived

[peak blaze]

@safe rapids Has your question been resolved? If so, type !solved :)

[safe rapids]

!solved