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#include <iostream>

class Base
{
public:
        int value;
        virtual int get_value_plus_one();
};

class Derived: public Base
{
public:
        int get_value_plus_one()
        {
                return value + 1;
        }
};

int main(){

        Derived d = Derived();
        d.value = 10;
        std::cout << d.get_value_plus_one() << std::endl;
}
/**
Compiler output:
/tmp/ccKnu9aW.o: In function `Base::Base()':
test.cpp:(.text._ZN4BaseC2Ev[_ZN4BaseC5Ev]+0x8): undefined reference to `vtable for Base'
/tmp/ccKnu9aW.o:(.rodata._ZTI7Derived[typeinfo for Derived]+0x8): undefined reference to `typeinfo for Base'
**/