Undifined reference to `vtable in for Base2 class

Question

I have the code below:

// IBase.h
#include <iostream>

class IBase{
    public:
           virtual string getId();
};

// IBase.cpp
#include "IBase.h"
string IBase::getId(){};

// Base.h
#include <iostream>
#include <string>
#include "IBase.h"

using namespace std; 
class Base : public IBase{
    protected:
           string id;
    public:
           Base(string _id);
           string getId();
};

// Base.cpp
#include "Base.h"

Base::Base(string _id){
    id = _id;  
}
string Base::getId(){
    return id;
}

// Base2.h
#include <iostream>
#include <string>
#include "Base.h" 
using namespace std;

class Base2 : public Base{
    public:
          Base2(string _id);
          string getId(); 
}; 

// Base2.cpp
#include "Base2.h"
Base2::Base2(string _id) : Base(_id){};

And i got the Undefined reference to `vtable in for Base2 when i compile the project! Is this i miss something?

Answer 1

Undefined reference to vtable usually indicates that the first virtual function(where the vtable is usually stored) was not linked.

As no definition for Base2::getId is provided(the first virtual function), no vtable gets linked.

Either add a definition for Base2::getId or remove the declaration for the function in the class definition.