why if we have pure virtual assignment operator in a base class, then we implement that operator on the derived class, it give linker error on the base class?
currently I only have the following explanation on http://support.microsoft.com/kb/130486 , it said that the behavior is by design since normal inheritance rules does not apply.
it is not clear for me, why is it generate linker error by design? can someone give me more clear explanation about this?
edit: added my simplified code of which the error occured:
class __declspec(dllexport) BaseClass {
public:
int memberA;
virtual BaseClass& operator=(const BaseClass& rhs) = 0;
};
class __declspec(dllexport) DerivedClass : public BaseClass {
public:
int memberB;
DerivedClass():memberB(0) {}
virtual BaseClass& operator=(const BaseClass& rhs) {
this->memberA = rhs.memberA;
this->memberB = 1;
return *this;
}
};
int main(void)
{
DerivedClass d1;
DerivedClass d2;
BaseClass* bd1 = &d1;
BaseClass* bd2 = &d2;
*bd1 = *bd2;
}
the code will compile with no errors without __declspec(dllexport)
and/or without pure virtual operator= declaration on base class.
without __declspec(dllexport)
after assignment of *bd1 = *bd2;
, d1::memberB is 1, but with __declspec(dllexport)
d1::memberB is left unchanged
with __declspec(dllexport)
, and without pure virtual declaration, after assignment of *bd1 = *bd2;
, d1::memberB is left unchanged