Question

I’m still learning C++; I was trying out how polymorphism works and I got a segmentation fault when calling a virtual method.

(Note: I didn’t mark the destructor as virtual, I was just trying out to see what happens.) Here’s the code:

#include <iostream>  using namespace std;  class Base { protected:   char *name;  public:   Base(char *name)   {     cout << name << ': Base class cons' << endl;   }    ~Base()   {     cout << name << ': Base class des' << endl;   }    virtual void disp(); };  void Base::disp() {   cout << name << ': Base disp()' << endl; }  class Child : public Base { public:   Child(char *name):     Base(name)   {     cout << name << ': Child class cons' << endl;   }    ~Child()   {     cout << name << ': Child class des' << endl;   }    virtual void disp()   {     cout << name << ': Child disp()' << endl;   } };   int main() {   //Base b;   //b.disp();   Base c = Child('2');   c.disp(); } 

Also, if you’ve any other tips regarding the usage of inheritance and polymorphism in general for someone who knows these concepts in Java, please let me know. Thank you!

Answer 1

name – is unintialized in Base

also you have another problem:

  Base c = Child('2'); 

I don’t think it’s what you want. Your code will create an instance of Base from casted Child. But I think you want work with Child instance based on Base interface; you should instead write:

  Base *c = new Child('2'); 

also, to avoid future bugs, declare destructor in base as virtual.