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c++inheritancepolymorphismdowncast

Downcasting and Virtual Functions

I was asked this question in an interview and I was unsure of the behaviour in the following case :

class A 
{ 
      virtual fun1(){...}
      virtual fun2(){...}
};

class B : public A
{ 
      virtual fun1(){...}
      virtual fun2(){...}
};

Now if,

A* AObj = new A;
B* BObj = (B*) AObj;

Does BObj have access to B's methods because of the virtual keyword or does it not because it's pointing to an object of AObj ?

Can someone help me with how exactly downcasting affects access also ?

Solution

  • Assigning an address of a base-class object to a derived-class pointer is undefined behavior. So anything can happen: calling BObj's functions can invoke B's functions, can invoke A's functions, can crash the program, or even format your hard drive. This will all depend on compiler and its optimization options.