CS35 - Fall 2017

Lab 02 Agenda

Clone lab02 and updating examples
Using Makefiles
Inheritance and Polymorphism
File I/O
Working with partners

Clone lab02

This is the same as lab01. Remember to run ssh-add when you log in, so you don't get repeatedly asked for you ssh password. Go to the CS35 github org, you can find the clone link for your repo on the web interface.

$ cd ~/cs35
$ git clone <link you got from github> ./lab02

You should also update your examples repository by going in your examples directory and pulling the updated version of the repository

$ cd ~/cs35/examples/
$ git pull

Using Makefiles

So far, we have always compiled our projects using the clang++ compiler directly, even when the project consisted of multiple files. This becomes rather inefficient for large projects, so today, we introduce a much more efficient way of compiling projects: Makefiles.

Go to the ~/examples/week-03/shapes folder and execute the command ls to get the list of files. Just as for Lab01, there are three .cpp files here that must be compiled together. We could compile them using

$ clang++ -std=c++11 -o testShape main.cpp circle.cpp rectangle.cpp

But instead, this time, we will use a Makefile. Feel free to open the Makefile with your favorite text editor to see what is there, but we will not explain it this time. For now, you only need to know that you can compile everything in the folder by executing the command

$ make

and you can clean up the folder by erasing all the .o files and the executable file ./testShapes by executing the command

$ make clean

Inheritance and Polymorphism

Last week, we talked about basic Object Oriented Programming (OOP) in C++. For lab this week, we will extend these basic concepts with Inheritance and Polymorphism. Inheritance allows us to define derived classes that inherit functionality from a parent base class. Polymorphism allows methods called on a pointer to a base class to call implementations defined in a derived class.

Let's look at some examples in the ~/examples/week-03/shape/ folder. There are also examples in the ~/examples/week-03/dog/ folder.

Polymorphism requires us to define some methods as virtual or pure virtual. The virtual keyword is added to the front of a method declaration in the base class to indicate it may be implemented differently in a derived class. Appending =0; to the method declaration makes a method pure virtual. These methods are not implemented at all in the base class and must be implemented in the derived class.

In our examples, Rectangle and Circle are derived classes of the base Shape class. Each of these derived classes, declare the pure virtual methods of the base class as normal methods. To indicate these classes inherit from the Shape base class we use the following class definition syntax:

class Rectangle : public Shape { 
 /* body */
};

In main.cpp we show how to use polymorphism to get Shape pointers to act like Rectangles and Circles.

File I/O

See examples in the ~/examples/week-03/fileIO folder.

You will need to use something similar to parse your input files for lab02.

Working with Partners

In this lab, you and your partner will be sharing a common git repo on github. We will grade the final version that appears on github at the Sunday deadline. In addition to the usual add, commit, push cycle, you will need to use git pull to grab changes that your partner has pushed to your shared repo.

You should get in the habit of running git pull before starting your edits to make sure you have the latest copy. When are temporarily done with your edits, add, commit, push so your partner can know that you've made changes. In general, you and your partner should be working on the lab together, but it is important that each of you have access to the latest version of the code.