UMBC CMSC202, Computer Science II, Fall 1998, Sections 0101, 0102, 0103, 0104

9. Redesigning Classes

Tuesday September 29, 1998

Assigned Reading:  5.1-5.7

Handouts (available on-line):

Programs from this lecture.

Topics Covered:

• Exam 1 Topics

• Detailed discussion on the design of the BString class. Some of the design goals were:
  • ease of use
  • lots of error checking
  • compatibility with char * strings
   

• We looked at some client programs that use the BString class (see header file):

  • Use overloaded << and >> operators.
    Program and sample run.

  • Use of constructors, + for concatenate, the [] operator, overloaded comparison operators, automatic "user-defined" type conversion. It turns out that this use of automatic type conversion from BString to char * causes a memory leak.
    Program and sample run.

  • The [] operator returns a reference to char. So it is possible to assign new values to the characters in a BString object. We use this feature to convert a string to all upper case.
    Program and sample run.

  • We use the >> operator to read in a file name, then dump the contents of that file to the screen. Note that the >> operator can be used for file I/O as well as console I/O. Also, note that the correct use of the type conversion operator (without causing a memory leak) is awkward.
    Program and sample run.

  • Finally, we looked at the implementation of the BString class in detail and discussed the ramifications of various design and implementation decisions.

  • Next lecture, we will quickly look at a second implementation of the BString class that fixes some of the problems with the first implementation. (see header file and implementation.)