Data Structures and Algorithms

Lab 2: iSwat Media Library

Due on Sunday, September 18th at 11:59 PM. This is a team lab. You and your assigned lab partner(s) will complete this lab together. Make sure that you are familiar with the Partner Etiquette guidelines. You may discuss the concepts of this lab with other classmates, but you may not share your code with anyone other than course staff and your lab partner(s). Do not look at solutions written by students other than your team. If your team needs help, please post on the Piazza forum or contact the instructor or ninjas. If you have any doubts about what is okay and what is not, it’s much safer to ask than to risk violating the Academic Integrity Policy.

Overview

In this lab, you will write a small application for managing a library of multimedia files. You will:

Make use of polymorphism and inheritance
Gain further experience with C++
Work with your lab partner to develop a piece of software

Because this is a team lab, you and your partner will share a repository. The URL for your repository will be git@github.swarthmore.edu:cs35-f16/lab02-<your-teamname>. You should have received an e-mail informing you of your team name. You can also find your team’s repository by visiting the GitHub organization for this class.

iSwat Media Library

Source: OpenClipArt.org

Your task will be to develop a command-line program to manage media files. In particular, we are concerned with images, text, and online video clips in this assignment. You will write three classes – Image, Text, and Video – which extend a base class Media and implement common behavior. You will then implement a MediaLibrary class which will read information from a media library file and allow the user to list or open the media contained within.

Starting Code

Your repository should contain the following starter files. Those which you may need to change appear in bold.

media.h: The declaration of the abstract Media class.
text.h/text.cpp: The Text class that you will implement.
image.h/image.cpp: The Image class that you will implement.
video.h/video.cpp: The Video class that you will implement.
mediaLibrary.h/mediaLibrary.cpp: The MediaLibrary class that you will use to keep track of your Media objects.
main.cpp: The main function for your program.
manualTests.cpp: Another main method that you can use to experiment with your code.
Makefile: The script that builds your code for you.

The `Media` Class

The Media class contains virtual methods which are common to all media. You will implement each of these methods in the Image, Text, and Video subclasses. See the method comments on the declarations of those classes for information about the behavior you need to implement.

The `MediaLibrary` Class

This class keeps track of the Media objects in a library. It allows a caller to ask how many Media objects there are and gives access to them upon request. Its constructor will read a media library file and create the Media objects accordingly.

The Media Library File

Source: OpenClipArt.org

When the program starts, it must be given a media library file as its only command-line argument, like so:

./iswatmedia test.library

Your MediaLibrary constructor will need to read the contents of this file and create an appropriate collection of Media objects for it. The first line of the file indicates the number of media items in the file. Each item is represented by several lines depending upon what kind of media it is:

For a text file, the next line will be text. The following line will contain the name of the text file (e.g. /usr/local/doc/GettysburgAddress); the next line will contain the document’s title (e.g. Gettysburg Address).
For an image, the next line will be image. The following line will contain the name of the image file (e.g. /usr/swat/pics/brownflames.gif); the next line will contain the image’s title (e.g. Brown Flames).
For a video clip, the next line will be video. The following line will be the URL for the video (e.g. https://vimeo.com/28241047). The line after that will be the title of the video (e.g. Running Gerbil). The next line after that will be the video length as a string (e.g. 00:29).

For instance, the following is a valid media library file:

3
image
/usr/swat/pics/brownflames.gif
Brown Flames
image
/usr/swat/pics/aliens.jpg
Aliens
text
/usr/local/doc/GettysburgAddress
Gettysburg Address

The Application

As mentioned above, your main function should take the name of a media library file as its only argument. Using that file, it should display a menu listing the media files (in order) and allow the user to pick a media file to open. Media files should be listed by positive integers (that is, the first media file you show should be selected by the input 1). After opening that media file, the menu should be repeated again; the program should continue in this fashion until zero is entered, after which it should terminate.

To display the media in a menu, you need to have a way of representing it. The describe method is virtual and unimplemented; each Media subclass implements it in a different way.

The getDescription method on Text should give the string "[text] " followed by the name of the document (e.g. "[text] Gettysburg Address").
The getDescription method on Image should do likewise but with the prefix "[image]" (e.g. "[image] Brown Flames").
The getDescription method on Video uses the prefix "[video]" and suffixes the video length in parentheses (e.g. "[video] Running Gerbil (00:29)").

The act of opening a media file is also performed by the particular Media subclass. The open method of each Media object should behave as follows:

The open method on Text should open the file, read it line by line, and print each line it reads.
The open method on Image should open the image viewer gpicview to display the image to the user. You can accomplish this by using the system function discussed below.
The open method on Video should open the URL of the video using firefox. You should use system for this as well.

The `system` Function

Source: OpenClipArt.org

The library cstdlib contains a function system which can run commands for you. You pass a C-style string to the system function and it will run it in much the same way as the shell we use to e.g. compile our programs. For instance, the following program will open Firefox to the Google home page. After it does that, it will open a text editor.

#include <cstdlib>
#include <string>

using namespace std;

int main(int argc, char** argv) {
    string cmd1 = "firefox http://www.google.com";
    string cmd2 = "gedit";

    system(cmd1.c_str());
    system(cmd2.c_str());

    return 0;
}

In larger applications, we avoid using the system function in favor of more precise ways to launch other programs from within our own code. For this lab, however, the system function suits us quite well.

Invalid Input

In this lab, you are not permitted to assume that the user gives valid input. The user may mistype the name of the media library file, for instance, or give a string instead of a number when you ask which file to open. Your program must handle these situations gracefully. If the user gives a string rather than a number, for instance, you should print an appropriate error message and then show the menu again. If the media library file does not exist, you should print a message and then quit (with a non-zero exit code, if you like).

To deal with the user typing an incorrect input for the menu, try reading the entire line that the user inputs and then converting that line into a string using the stoi function. You can then catch any exception that the stoi function raises, like so:

string inputLine;
getline(cin, inputLine);
try {
  int choice = stoi(inputLine);
  // If you reach this line, then everything is fine.
} catch (exception& e) {
  // If you reach this line, then something went wrong!
}
// You will reach this line either way.

Exceptions in C++ work much like they do in Python and Java.

You are permitted to assume that, if a media library file exists, it is formatted correctly; you do not have to worry about e.g. the file being empty or containing a non-integer on the first line.

Getting Started

Remember: you don’t have to write every program all at once. Consider using the following approach to completing your lab assignment:

Complete the code for the Text class first. A little bit more of that code has been provided for you.
A file manualTests.cpp exists for your convenience. In that file, write some code that creates a Text object and calls both getDescription and open. Make sure it does what you think it should do. Until it does, don’t write new code. Get the Text class to work correctly before continuing on to the rest of the lab.
Based on your work on Text, implement the Image and Video classes. They will be similar, but not identical.
Next, write your MediaLibrary class. Again, try writing a few short snippets of code to see if it works.
Finally, write your main function to construct the MediaLibrary object, present a menu, and open media files until the user decides to quit.

The approach described above – writing a little bit of your program and then writing some tests to see if things work correctly – is a powerful skill. By testing pieces of your code in isolation, you gain confidence in your implementation and it becomes easier to track down bugs and, at a higher level, understand what your code is doing.

Coding Style Requirements

You are required to observe some good coding practices:

Source: OpenClipArt.org

You should pick meaningful variable names.

// Good
int* pixels = new int[size];
// Bad
int* p = new int[size];

You should use correct and consistent indentation. Lines of code within a block (that is, surrounded by { and }) should be indented four spaces further than the lines surrounding them.
```
// Good
if (condition) {
    cout << "Test" << endl;
}
// Bad
if (condition) {
cout << "Test" << endl;
    }
```
You should use a block whenever possible, even if it’s not necessary. This helps you avoid subtle or messy bugs in the future.
```
// Good
if (condition) {
    cout << "Something" << endl;
}
// Bad
if (condition)
    cout << "Something" << endl;
```

Peer Review

As this is a team assignment, you are required to complete a peer review of your lab partner or partners. You must do this even if everything is fine. You should complete this peer review after you have turned in your assignment. The peer review comes in the form of a simple Google Form and can be accessed here; in most cases, it will likely take less than a minute to complete. If you have trouble accessing this peer review, please make sure that you are logged into Google using your Swarthmore credentials.

Your peer review will be kept private; only course staff will have access to this information. You can also update your peer review after you have submitted it. However, if you do not submit a peer review, you will lose participation grade points. Please don’t forget!

Summary of Requirements

Your program should

Have a different Media subclass for each of the three kinds of media
Use the MediaLibrary constructor to read a media library file and create appropriate Media objects
Use polymorphism to address how each different type of Media object is opened
Use the system function to launch helper programs as described above
Validate user input and respond appropriately if invalid input is given

Example Execution

Here’s an example run of the program:

$ ./iswatmedia example1.library
1. [image] Brown Flames
2. [image] Aliens
3. [text] Gettysburg Address
0. (quit)
1

1. [image] Brown Flames
2. [image] Aliens
3. [text] Gettysburg Address
0. (quit)
3

  Four Score and seven years ago our fathers brought forth on
this continent a new nation, conceived in Liberty, and dedicated
to the proposition that all men are created equal.
  Now we are engaged in a great civil war, testing whether that
nation, or any nation so conceived and so dedicated, can long endure.
We are met on a great battle-field of that war. We are met to dedicate
a portion of it as the final-resting place of those who here gave
their lives that that nation might live. It is altogether fitting
and proper that we should do this.
  But in a larger sense we cannot dedicate, we cannot consecrate, we
cannot hallow this ground. The brave men, living and dead, who
struggled here, have consecrated it far above our power to add or
detract. The world will little note nor long remember what we say
here, but it can never forget what they did here. It is for us, the
living, rather to be dedicated here to the unfinished work that they
have thus far so nobly carried on. It is rather for us to be here
dedicated to the great task remaining before us, --that from these
honored dead we take increased devotion to the cause for which they
here gave the last full measure of devotion, --that we here highly
resolve that the dead shall not have died in vain, that the nation
shall, under God, have a new birth of freedom, and that the
government of the people, by the people, and for the people, shall
not perish from the earth.


1. [image] Brown Flames
2. [image] Aliens
3. [text] Gettysburg Address
0. (quit)
-1
Invalid entry.

1. [image] Brown Flames
2. [image] Aliens
3. [text] Gettysburg Address
0. (quit)
brown flames
Invalid entry.

1. [image] Brown Flames
2. [image] Aliens
3. [text] Gettysburg Address
0. (quit)
0

Goodbye!
$ ./iswatmedia eggsample1.library
Your media library is either empty or invalid.
$

Lab 2: iSwat Media Library

Overview

iSwat Media Library

Starting Code

The Media Class

The MediaLibrary Class

The Media Library File

The Application

The system Function

Invalid Input

Getting Started

Coding Style Requirements

Peer Review

Summary of Requirements

Example Execution

The `Media` Class

The `MediaLibrary` Class

The `system` Function