CMSC 202 Computer Science II, Spring 2007, Section 010x

Lecture 12: Copy Constructors

Thursday 03/08, 2007

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Assigned Reading:  10.3

Slides As Shown:

• Announcements, etc: [slide view] [print view]

• Destructors, Copy Constructors and the Assignment Operator : [slide view] [print view]

Topics Covered:

• Reminder: Midterm exam is next Thursday, March 15. Please bring a photo ID unless you know that I know that you know that I know who you are.

• Went over list of topics that are fair game for Exam I. (See announcement slides.)

• Discussed destructors and the fact that they are invoked automatically in many different situations. (See slides above and links to programs below.)

  Examples:

  • A class DMC with a dynamically allocated array: dmc.h, dmc.cpp.
  • A simple example with destructors being invoked when objects go out of scope: main1.cpp.
  • Destructors and loops: main2.cpp.
  • Temporary objects in expressions: main3.cpp.
  • DMC as data member in AClass: main4.cpp.

• Danger of destructors: objects are copied in many situations. We need to make sure that the copies are deep copies and not shallow copies. Otherwise, when a destructor is called it frees the memory that other objects are still pointing to.

  Examples of bad behavior:

  • Using delete instead of delete [] : bad1.cpp.
  • After assignment: bad2.cpp.
  • After initializing with DMC X = DMC(Y) : bad3.cpp.
  • Passing a DMC by value: bad4.cpp.
  • Passing by a DMC value: bad5.cpp.

• For classes with dynamically allocated members, we need to implement a copy constructor and an overloaded assignment operator to perform the deep copying. (See slides.)