2.6 Shallow & Deep Copying

If We Never Write Our Own   

If our data members do not have explicit copy constructors (and their data members do not have explicit copy constructors, and …) then the compiler-provided copy constructor amounts to a bit-by-bit copy.

Shallow vs Deep Copy   

Copy operations are distinguished by how they treat pointers:

• In a shallow copy, all pointers are copied.
  • Leads to shared data on the heap.
• In a deep copy, objects pointed to are copied, then the new pointer set to the address of the copied object.
  • Copied objects keep exclusive access to the things they point to.

Shallow copy is wrong when...   

• Your ADT has pointers among its data members, and
• You don’t want to share the objects being pointed to.

Compiler-generated copy constructors are wrong when...   

• Your ADT has pointers among its data members, and
• You don’t want to share the objects being pointed to.