What is the difference between shallow copy and deep copy?

When copying an object that contains pointer members, the behavior depends on whether you do a shallow or deep copy: Shallow copy: copies only the pointer value — both objects point to the same underlying data. The compiler-generated copy constructor performs a shallow copy. class ShallowArray { int* data; int size; public: ShallowArray(int s) : data(new int[s]), size(s) {} // Default copy constructor (shallow): // Copies data pointer, not the array // Both original and copy point to same memory! }; ShallowArray a(5); ShallowArray b = a; // Shallow -- b.data == a.data delete[] a.data; // Now b.data is dangling!. Problems: double deletion (undefined behavior when both objects are destroyed), modifying through one object affects the other. Deep copy: allocates new memory and copies the contents: class DeepArray { int* data; int size; public: DeepArray(int s) : size(s), data(new int[s]) {} // Deep copy constructor: DeepArray(const DeepArray& other) : size(other.size), data(new int[other.size]) { std::copy(other.data, other.data + size, data); } // Deep copy assignment: DeepArray& operator=(const DeepArray& other) { if (this != &other) { delete[] data; size = other.size; data = new int[size]; std::copy(other.data, other.data + size, data); } return *this; } ~DeepArray() { delete[] data; } }; DeepArray a(5); DeepArray b = a; // Deep -- separate copy of array. Modern solution: use std::vector<int> instead of raw arrays — its copy constructor performs a deep copy automatically (Rule of Zero). Shallow copy is appropriate when sharing ownership (std::shared_ptr handles this with reference counting).