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

8. Designing Classes

Thursday September 24, 1998

Assigned Reading:  4.6-4.13

Handouts (available on-line): Project 2

Programs from this lecture.

Topics Covered:

• Discussed Project 2.

• Took attendance.

• Continued with C++ I/O:

  • Example 6: file I/O. We use the open() and close() member functions of an ifstream and ofstream object to open and close a file for reading and writing, respectively. Once open, we can use the << and >> operators with the stream objects as we've done with cin and cout. Note the use of the eof() member function to detect the end of file.
    Program and sample run.

  • Example 7: we modify our GetLine() function to work with file I/O as well as console I/O. The only tricky part is that we need to test for the end-of-file condition. In order to trigger an eof condition, we must attempt to read past the end of the file. So, at the beginning of the function, we read in one character, then test for eof. If we are not at the end of the file, then we use nifty putback() function to pretend that we didn't read that extra character. The result is a GetLine() function that works with input files and with cin.
    Program and sample run.
   

• The GetLine() function shown above is ugly. It was developed without regard to object-oriented philosophy. We discussed how we might develop an object-oriented string class that allows strings to shrink and grow as we need more or less space. One possible many possible designs is the BString class declared in the header file bstring.h. Sample programs show that one of the design goals of this class is to allow the user to use BString objects and char * strings somewhat interchangeably.
  • First program and sample run.
  • Second program and sample run.
   
  The implementation of the BString class will be discussed in the next lecture.