CMSC 202 Computer Science II, Fall 2015, Section 06

Lecture 7: Objects & Classes

Thu 09/17, 2015

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Assigned Reading:  7.1-7.3

Slides As Shown:

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

• Object-Oriented Classes : [slide view] [print view]

• Encapsulation : [slide view] [print view]

Topics Covered:

• Intro to Classes.

• Demonstrate that private is not intended to be secure in C++:
  • The first example priv1.cpp shows that non-member functions cannot access private members. Compiling this program is a syntax error. (See sample run.)
  • For the second example priv2.cpp we add a public constructor that initializes data members and a dump() member function to print out data. (See sample run.)
  • In the third example, priv3.cpp, we use a pointer to change the value of the public data member. (See sample run.)
  • In the fourth example, priv4.cpp, we use change the pointer to point to private member priv_data. (See sample run.)
  • In the fifth example, priv5.cpp, we made both data members private, but we can still point to the data members using the address of the object and changing the type address. (See sample run.)

• Most C++ programs have separate header files and implementation files. Here, priv.h has the declaration of the foo class. The implemenation of the member functiosn are in priv.cpp. When main1.cpp is compiled with priv.cpp the effect is the same as with priv5.cpp. (See sample run.)

  Alternatively, we can use a modified version of the header file privhack.h which does not have private data members. Even though the definition of class foo has been modified, it remains compatible with the compiled implemenation of the member functions. (See main2.cpp and sample run.)