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The Assignment Operator

The Assignment Operator. Rule of Three. Any object which manages memory needs: Custom Destructor Custom Copy Constructor Custom Assignment Operator (now). Copy Constructor. Generally need a deep copy not a shallow one: YES NO. Copy Constructor Recipee. Basic copy constructor recipe:.

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The Assignment Operator

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  1. The Assignment Operator

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

  3. Copy Constructor • Generally need a deep copy not a shallow one: YES NO

  4. Copy Constructor Recipee • Basic copy constructor recipe:

  5. Using Copy Ctor Explicitly • Explicit copy constructor call:

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

  7. Using Assignment Operator • Assign existing object uses assignment operator

  8. Default Assignment Operator • Every class gets default assignment operator • Copies each member directly: • Shallow copy!!!

  9. 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

  10. 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 • Differences: • Signature : returns a object reference • Already have an object… which already owns memory • Have to watch for self assignment

  11. 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)

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

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

  14. Copy Constructor First Pass… • On assignment: • Two existing objects • Want to turn one into deep copy of other course2 = course1course2.=(other)course2 is thiscourse1 is other

  15. Copy Constructor First Pass… Copy basics:

  16. Copy Constructor First Pass… Delete oldstorage

  17. Copy Constructor First Pass… Allocate newstorage andcopy data

  18. Copy Constructor First Pass… Return theobject that wascopied into

  19. Self Assignment Danger • Self assignment will clear an object / blow up your program:

  20. Bad Self Assignment Copying basicinfo does nothing

  21. Bad Self Assignment Deleting wipes outstorage!!!

  22. Bad Self Assignment Allocate a newempty array

  23. Bad Self Assignment Loop either copiesempty objectsor maybe blowsup

  24. Bad Self Assignment Loop either copiesempty objectsor maybe blowsup

  25. Final Version • Final version : • Compare address of self to address of otherOnly copy if not same

  26. Recipe • Basic recipe:

  27. Applied to ArrayList • Combine operator overloads with templates and we get a much easier to use array:

  28. Vectors • Vector is C++'s official ArrayList • Programmers should use instead of arrays most of the time • We'll study week 10 • Take a peek if you want Ch 12.6-12.8

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