1. Rule Of Three Part 3

2. Rule of Three Any object which manages memory needs: Custom Destructor
Custom Copy Constructor
Custom Assignment Operator

3. Rule of Three Any object which manages memory needs: Custom Destructor
Custom Copy Constructor
Custom Assignment Operator

4. Using Copy Ctor Explicitly
Explicit copy constructor call:

5. Using Copy Ctor Implicitly
Initialization while declaring uses copy constructor:

6. Using Assignment Operator
Assign existing object uses assignment operator

7. Default Assignment Operator
Every class also default assignment operator
Copies each member directly:
Shallow copy!!!

8. Custom Assignment Operator
Custom assignment operator similar to copy constructor
Copy over basic information
Allocate own dynamic memory
Copy values that are in dynamic memory
BUT…
Usually returns a reference to the object
Already have an object… which already owns memory

9. Custom Assignment Operator
Course assignment operator:
I will return a reference to the course
that we are copying into
I take a reference to a course we will not change
Interpreted as course2.=(course1)

10. Why return reference Chained assignments are allowed in C++
Only makes sense if y = 2 resolves to y when done

11. Why return reference Chained assignments are allowed in C++ y
Only makes sense if y = 2 resolves to y when done y

12. Assignment First Pass…
On assignment:
Two existing objects
Want to turn one into deep copy of other
course2 = course1 course2.=(other) course2 is this course1 is other

13. Flawed first attempt…
Copy basic stuff

14. Flawed first attempt…
Delete old storage

15. Flawed first attempt…
Allocate new storage

16. Flawed first attempt…
Copy data

17. Flawed first attempt…
Return the object that was copied into

18. Self Assignment Danger
Flaw : self assignment deletes data

19. Bad Self Assignment
Deleting wipes out storage!!!

20. Bad Self Assignment
Allocate a new empty array

21. Bad Self Assignment
Loop either copies empty data or blows up array up

22. Final Version Avoid modifying on self assignment:
If address of other is same as this (my address), don't copy

23. Assignment Operator Recipe
Assignment Process
Step
Pseudocode
Verify not self assigning
Copy basics
Delete old memory Make new array
Copy array
No matter what, return self
if( this != &other) {
this.size = other.size
… delete [] array
array = new whatever[other.size]
for(i = 0 to other.size -1) array[i] = other.array[i] }
return *this

24. Book Bug Assignment Operator covered in 14.13, but has typos
Does not copy data to new array
Missing self assignment check