Undefined reference to 'vtable for xxx'

Question

takeaway.o: In function `takeaway\':
project:145: undefined reference to `vtable for takeaway\'
project:145: undefined reference to `vtable for takeaway\'
takeaway.o         


        

Answer 1

If a class defines virtual methods outside that class, then g++ generates the vtable only in the object file that contains the outside-of-class definition of the virtual method that was declared first:

//test.h
struct str
{
   virtual void f();
   virtual void g();
};

//test1.cpp
#include "test.h"
void str::f(){}

//test2.cpp
#include "test.h"
void str::g(){}

The vtable will be in test1.o, but not in test2.o

This is an optimisation g++ implements to avoid having to compile in-class-defined virtual methods that would get pulled in by the vtable.

The link error you describe suggests that the definition of a virtual method (str::f in the example above) is missing in your project.