copy constructor in c++ deep copy shallow copy...

Copy Constructor

·           A special kind of constructor in C++

·           Creates a new object as a copy of an existing one

·           There exists an implicit copy constructor in all classes in C++ that do not define one

·         Unfortunately, it only creates a shallow copy of all the data members

·       This will create problems when a class has data that involves pointers to dynamic memory

Deep copy and shallow copy ::

·           Shallow copy – used to copy direct values

·         If you make a shallow copy of a pointer, you would have two pointers that point to the same location

·           Deep copy – used to copy indirect values

·         If you make a deep copy of a pointer, you will have two pointers that point to different locations but those locations have the same value

·           Modifying the original object should not affect its copy or vice versa

·           Explicit Use:

·         Building a(4);     // standard constructor call

·         Building b(a);     // b is now a deep copy of a

·           Implicit Use #1:

·         Building a(4);     // standard constructor call

·         Building b = a;    // implicit call to the copy constructor

·           Implicit Use #2:

·         When an object is returned by value from a function

·           Common Misunderstanding:

·         Building a(4);     // standard constructor call

·         Building b(3);     // standard constructor call

·         b = a;                          // does NOT call copy constructor

·           The copy constructor is never called in this code

·           The last line uses the assignment operator which may be overloaded in C++

Destructor

l For an object created on the stack:

-     the destructor is automatically invoked when the object goes out of scope

l For an object that was dynamically allocated on the heap:

-     the destructor called when the “delete” command is used on the object