Computer Science 381
Programming Unix in C

Winter Immersion 2016, The College of Saint Rose

Lab 8: "Object-Oriented" C
Due: Friday, January 8, 2016

In this lab, you will see how to develop a data structure in C using a somewhat "object-oriented" methodology, despite the lack of language features to support object orientation.

Previous Example Revisited

One of the last lab's examples demonstrates this: the ratio.h and ratio.c files.

The structure definition and the four functions provide similar capabilities to a class in a language like Java. The fields of the structure are like instance variables of a Java class (though they would be more like public rather than the preferred protected or private instance variables). The create_ratio function plays the role of a constructor. The other functions are like the methods of a class.

Notice, however, that we have no mechanism for real data hiding. Anyone with access to a pointer to a ratio can access and modify the data fields. In fact, with the ability to use casts, we could treat the memory that was allocated as a ratio in completely unexpected (and likely incorrect) ways.

Also, all calls to functions that operate on a ratio must take the ratio as a parameter. So what would be something like


in an object-oriented language would be


here. This is what actually happens behind the scenes with real objects.

Practice Program: Add a function print_ratio_mixed to ratio.c and a function prototype to ratio.h that will print a ratio as a mixed number. For example, if the numerator field is 8 and the denominator field is 3, it would print as "2 2/3" instead of "8/3". (5 points)

A More Complex Example

Consider this example, which is an implementation of a singly-linked list structure that holds int values.

See Example:

Study this code to make sure you know how it works.

Question 1: Briefly explain why it is important to provide separate .h and .c files for an implementation of a data structure such as this. (4 points)

Question 2: Draw a memory diagram showing the state of the program's memory just before it executes the printf statement at line 68 of slltest.c. Differentiate between stack variables (the contents of parameters and/or local variables of functions in execution) and heap variables (everything allocated with malloc). (6 points)

Programming Assignment: A C Q

Develop a queue structure and corresponding functions to operate on queues in C that hold int values. Include an approrpriate header file, implementation file, and a separate file with a main function that tests your implementation. Also include a Makefile that compiles your queue implementation and your testing code.

Recall that a queue is a first-in, first-out structure that should be able to be constructed, enqueue elements, dequeue elements, and answer whether it is currently empty. You should also be able to deallocate the queue.

This program and its Makefile are worth 25 points.

The executable for the reference solution to this program is available on mogul in /home/cs381/labs/ooc.


Please submit all required files as email attachments to terescoj AT by Friday, January 8, 2016. Be sure to check that you have used the correct file names and that your submission matches all of the submission guidelines listed on the course home page. In order to email your files, you will need to transfer them from mogul to the computer from which you wish to send the email. There are a number of options, including the sftp command from the Mac command line.


Grading Breakdown

print_ratio_mixed function 5 points
Lab questions 10 points
int queue correctness 15 points
int queue error checking 2 points
int queue memory management 2 points
int queue documentation 3 points
int queue style 2 points
Makefile for queue program 1 point