Note: a missing vtable usually means the first non-inline virtual member function has no definition.

A missing vtable usually means the first non-inline virtual member function has no definition.

Explanation:

• A virtual member function in C++ is a function that can be overriden by derived classes.
• When a class contains a virtual function, it typically has what’s called a vtable (virtual function table).
• The vtable is a data structure that holds pointers to the virtual functions of the class.
• However, if the first non-inline virtual member function of a class has no definition (i.e., no implementation), the compiler will not generate a vtable for that class.

Example:

    
#include <iostream>
using namespace std;

class Base {
public:
    virtual void foo() = 0;
};

class Derived : public Base {
    virtual void foo() {
        cout << "Derived foo()" << endl;
    }
};

int main() {
    Base* b = new Derived();
    b->foo();
    return 0;
}