C++ Error when using virtual destructor

Question

I have implemented an interface:

class ISolution
{
public:
  virtual ~ISolution() = 0;

  virtual void resultat() = 0;
};

and some derived classes from it:

class SolX : ISolution
{
private:
  int member;
  MyClass myOb;
public:
  SolX(const MyClass& inOb) : myOb(inOb) {}
  ~SolX() {}

  void resultat()
  {
    // the body
  }
};

When I compile it I get errors like:

/proj/CSolution1.cpp:4: undefined reference to `ISolution::~ISolution()'
/proj/CSolution2.cpp:4: undefined reference to `ISolution::~ISolution()'
CMakeFiles/proj.dir/CSolution2.cpp.o:/proj/CSolution2.cpp:12: more undefined references to `ISolution::~ISolution()' follow

I am using CMake and Linux Ubuntu.

I cannot figure out what is the problem. Is there something that I have missed? Does myOb create the problems?

P.S.: The line where is the error is at the definition of the constructor.

Answer 1

The problem is

virtual ~ISolution() = 0;

the destructor is not implemented. Try

virtual ~ISolution() { }

instead.

This is needed even when only instances of the derived class are created, because destructors are special. In a normal function, the base class implementation needs to be called explicitly, like

void Derived::Foo() {
    Base::Foo();
    ....
}

but for a destructor, this is always done automatically.