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c++ooppolymorphismlate-binding

LateBinding with dynamic memory

I have Base and Derive class at the below which related to polymorphism (Latebinding) :

 class Base
{
....
};

class Derive:public Base
{
....
};

int main()
{
  int n;
  cin>>n;
  Base *pt;
  pt=new Derive[n];
  
  for(int i=0;i<n;i++)
     pt[i].Input(); 
}

While I was inputing the first index of pt[0] it's fine, but in index[1] the program is forced to close. Any idea why?

Solution

  • An array of Base is not an array of Derived. A Derived instance can be larger than a Base, and then address calculations go haywire when the array is treated as array of Base. For this reason the standard specifies Undefined Behavior in this case.

    Instead you can use an array of pointers to Base.