ABCs (abstract base classes) and linkage problems

I m getting a ton of linkage errors (unresolved externals) when using an
abstract base class. My classes look something like this:

class BaseObject
{
    //pure virtuals
    virtual void foo() = 0;
    virtual int foobar(int, int, double) = 0 ;

    virtual void grok();
    virtual int doit();
}

class MyClass : public BaseObject
{
    //pure virtuals are implemented
    void foo() {...}
    int foobar(int a, int b, double c){return 42;}

    //these are not implemented .. and not called in code
    //virtual void grok();
    //virtual int doit();

}

Linkage errors (unresolved externals):

BaseObject::BaseObject(void)
void grok()
int doit();

which leads to my questions:

i). Why is the linker looking for the constructor of the ABC BaseObject?
ii). Do I need to implement the constructor of BaseObject ? (this goes
against my understanding of most languages definition of an interface)
iii).Why is the linker looking to resolve the two (non pure) virtuals in
the interface - I dont use it any where in the code - and it is only
there for "future comapatability"

What am I doing wrong ?