Question

I was wondering how this piece of code gives a memory access violation?

{
   Vector3f *a = new Vector3f [10];
   Vector3f *b = a;
   b[9] = Vector3f (2,3,4);
   delete[] a;
   a = new Vector3f [10];
   b[4] = Vector3f (1,2,3);
   delete[] a;
}

Answer 1

Because b still points to the same array as a when you call delete[] a, and then you try to use that memory with b[4].

Vector3f *a = new Vector3f [10]; // a initialised to a memory block x
Vector3f *b = a;                 // b initialised to point to x also
b[9] = Vector3f (2,3,4);         // x[9] is assigned a new vector
delete[] a;                      // x is deallocated
a = new Vector3f [10];           // a is assigned a new memory block y
b[4] = Vector3f (1,2,3);         // x is used (b still points to x)
                                 // x was deallocated and this causes segfault
delete[] a;                      // y is deallocated