How to inherit from an abstract class properly in C++?

I couldn't find a proper topic for this question as I haven't got a proper error message.

I'm trying to create a management system for a restaurant which mainly provides pizza as well as other foods(pasta, wings, etc). I want this system to be used by the staff. I have created an abstract class named Foods that can be used to inherit by other foods. So far I have created a class that inherits from Foods named Pizza. Below are my code.

PS: I have used namespaces for organize foods and staff members separately. As far as I know some people doesn't recommend namespace and my apologies if you're one of them.

interfaces.h

#include <vector>
#include <string>

namespace foods{
    class Food{
        double price;
        // since the sauces and drinks are given with foods.
        static const std::vector<std::string> sauces;
        static const std::vector<std::string> drinks;
    public:
        virtual int retPrice() = 0;
        virtual void ask() = 0; // ask user what to add
        virtual ~Food() = default;
    };
    const std::vector<std::string> Food::sauces = {"Blue cheese", "Garlic", "Honey BBQ", "Marinara"};
    const std::vector<std::string> Food::drinks = {"Pepsi", "Mountain Dew", "Coca Cola"};

    class Pizza: public Food{
        const double price;
        const std::string pizzaType; // whether it is chicken, beef, etc.
        const std::string size; // small, medium or large
    
        int crust = 1; // how crust it is from 1-5
        std::vector<std::string> toppings; // to store toppings
    public:
        Pizza(): price(15), pizzaType(" "), size(" "){}
        int retPrice() override; // the price should change according to the type
        void ask() override; // ask the customer for a pizza

        void createACustom(); // create a custom pizza with desired toppings
    };
};

functions.cpp

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

namespace foods{
    int Pizza::retPrice(){
        return (price+5);
    }
    void Pizza::ask(){
        std::cout << "Hello World!";
    }
}

test.cpp

#include "interfaces.h"

int main(){
    foods::Pizza* pizza = new foods::Pizza();
}

And I'm getting following error.

/usr/bin/ld: /tmp/ccQRR5B8.o: warning: relocation against `_ZTVN5foods5PizzaE' in read-only section `.text._ZN5foods5PizzaC2Ev[_ZN5foods5PizzaC5Ev]'
/usr/bin/ld: /tmp/ccQRR5B8.o: in function `foods::Pizza::Pizza()':
test.cpp:(.text._ZN5foods5PizzaC2Ev[_ZN5foods5PizzaC5Ev]+0x2b): undefined reference to `vtable for foods::Pizza'
/usr/bin/ld: warning: creating DT_TEXTREL in a PIE
collect2: error: ld returned 1 exit status

I tried using the keyword override and also made a default deconstructor, yet nothing seems working. I want to know what this error message means and a solution for this. In addition to that what is vtable?

Appreciate your time and answers.

EDIT 1

I have compiled it with g++ -Wall -Wextra test.cpp functions.cpp -o test, which is wrong and then I did g++ -Wall -Wextra test.cpp functions.cpp -o test and I'm getting following error.

/usr/bin/ld: /tmp/ccmv2G17.o:(.bss+0x0): multiple definition of `foods::Food::sauces[abi:cxx11]'; /tmp/ccuBNQjX.o:(.bss+0x0): first defined here
/usr/bin/ld: /tmp/ccmv2G17.o:(.bss+0x20): multiple definition of `foods::Food::drinks[abi:cxx11]'; /tmp/ccuBNQjX.o:(.bss+0x20): first defined here
collect2: error: ld returned 1 exit status

Why is it saying that it has multiple definitions?