Description
1 Introduction
In this semester we are located in the Art center, which sets the theme of art for
the assignments. This homework asks you to implement an in-memory database
to store art pieces of an art collector. The application starts with some given
budget and then the input file contains art pieces that art collector is going to
buy. After the input file has been processed, the application should print the
content of the in-memory database as well as remaining budget and worth of
the art collection.
Goal of this homework is to get your hands dirty with programming in C
language and become more familiar with the Linux environment. You need to
implement an application that resembles a very simple in-memory database. It
will help you to learn some of the C concepts, get familiar with C syntax, and
will give you an idea of how programs in C are written.
2 Setting Up SSH Connection (Optional)
As you may have seen, using VMWare interface to work with CLI (Command
Line Interface) of the VM may be not very convenient. There are several ways
how to deal with it within VMWare but we are going to try a different approach.
In the real world you may be working with remote servers even if you are frontend developers. In such case one of the most common solutions is to use so-called
SSH (Secure Shell) connection.
You can find more about SSH in the online resources below
https://en.wikipedia.org/wiki/Secure_Shell
http://blog.robertelder.org/what-is-ssh
2.1 Obtaining IP Address
To connect to your VM you need its IP address and its SSH connection port.
Default port for SSH is 22. To obtain its IP address, type the following in your
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VM terminal:
$ i p a
You should see two network interfaces. One should have an IP address
127.0.0.1 and another one should have some other IP address. We need that
second one, which is the IP address of your VM. Now we need an SSH client
to connect to your VM. Please read the appropriate subsection depending on
Operating System of your computer.
2.2 Linux OS
If you use Linux as your Operating System, most likely you already have the
SSH client. Open the terminal (it is an application) and type the following:
$ s s h vm l o gin@ vm ip add re s s
where you need to use your VM login instead of “vm login” and your VM
IP address (that we found earlier) instead of “vm ip adress”.
2.3 macOS
If you use macOS as your Operating System, you already have the SSH client.
Open the terminal (it is an application) and type the following:
$ s s h vm l o gin@ vm ip add re s s
where you need to use your VM login instead of “vm login” and your VM
IP address (that we found earlier instead) of “vm ip adress”.
I would recommend to learn and use an application called iTerm2 instead
of native terminal available in the Mac OS as it is rich in features. You can read
more about it in the corresponding documentation https://www.iterm2.com.
2.4 Windows
If you are Windows user, you have several options but I will focus on two
clients. One of the most used SSH clients for Windows is PuTTY. You can
find instruction how to use it online under the following link:
PuTTY instructions
NB: You don’t have to put PuTTY into “Windows” folder, you can put it
anywhere you want. Usually, the best place for PuTTY is a Desktop.
PuTTY is good enough, however, I would recommend to try SmarTTY.
It has several neat features and also simple to use. You can find more about it
online under the following link:
http://smartty.sysprogs.com
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2.5 Connection Refused
So we tried…
But we cannot connect as a remote host (your VM) keeps refusing access.
It happens because by default machines do not expect that someone can log
in into them. Let’s fix it. We need to install an SSH server first, so type the
following command in your VM’s terminal:
$ sudo apt−g e t i n s t a l l openssh−s e r v e r
If it will give you an error at the end, try perform update first and then
repeat the command to install the SSH server (you most likely can ignore error
from the update command):
$ sudo apt−g e t update
$ sudo apt−g e t i n s t a l l openssh−s e r v e r
Now, the connection through SSH should work. Moreover, finally you can
easily do copy and paste, have a much nicer screen resolution, and enjoy writing
in C! It is worth mentioning that you can do even more, e.g., use SCP or features
of a particular SSH client you may use. But that I recommend to learn on your
own by consulting corresponding documentation.
3 Your Programming Task
In this homework you need to implement an application called art collector.
The application takes commands from a given file to modify internal database of
art pieces and then return some result based on specified flags. You always start
with a clean database (it is very inefficient but for the sake of this assignment it
is okay) and then you start to modify you internal database implemented within
your C code based on the content of the given file. Regarding flags you will have
two scenarios:
• No flags provided. Then you need to print string NO QUERY PROVIDED.
• At least one flag is set. Then you need to print according to the flags.
Your program should work according to the following specification (being in
square brackets means to be optional):
$ a r t c o l l e c t o r fil e n am e −b N [−v ] [− i i d ]
[−t type ] [−n a r ti s t n am e ] [−o fil e n am e ]
• -v Print information about all art pieces in the database.
• -i Print information about all art pieces with matching ID.
• -t Print information about all art pieces with matching TYPE.
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• -n Print information about all art pieces with matching ARTIST NAME.
• -b Initial budget of N monies.
• -o Print information to the given file. If file does not exists then create
one. If file exists, then prompt user if file should be overwritten. If user
says “y” or “yes” then proceed. If user says “n” or “no” then exit and
print message FILE EXISTS.
Result of your program should be written to stdout unless flag “-o” is set.
Safe assumptions in this assignment are the following:
• You may assume that required arguments for flags are always provided.
• Commands (the very first word) in the input file are always in the upper
case.
You program should comply to the following constraints:
• You cannot use string libraries, e.g. <string.h>.
• You cannot use getopt() function to parse flags.
• You cannot use indices for arrays. You have to use pointers and pointer
arithmetic. It means that if you want to access the third element of the
array ptr, you have to use ptr + 2 instead of ptr[2].
• Art type in the database should always be capitalized.
• Art name and Artist name in the database should always start with capital
letter and the rest is lowercase.
• To store your art pieces records you will need to use some data structure. That data structure should be a linked list. It should be called
art pieces.
• You shall not modify the .travis.yml file.
• We should be able to compile your program using make command.
IMPORTANT: Failing to comply to any of the constraints may
result into 100% penalty for the grade or test case.
In the real world you may receive some set of constraints or assumptions.
However, it may be completely up to what to check and how to check to estimate
how correct is your application. As this is a course where you are still learning,
we provide you an idea of what you should check:
• Combination of flags is correct, e.g., “-v” flag cannot be combined with
any other flag except “-o”.
• Specified input file exists and can be opened.
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• Command in the input file is correct.
• Input data makes sense.
• Art piece ID should be unique.
IMPORTANT: You should print only what is asked. Otherwise,
you may file a test case and receive 0 points for it!
You may think that decorating your output or having just a minor difference
such as printing a dot after printed text is a very minor thing. However, when
you are asked to print a very particular result, it means that your output will
be expected to be in a very specified form. If you don’t follow the specification
it is not others people code cannot handle yours and it is bad. It is your code
is bad.
In general, it may be useful to use for your programming a combination of
Design by Contract and Defensive Programming. You use first when it is about
your output and you use latter when it comes to check all the inputs you have
received. You can easily search online what those terms mean though we may
cover that a bit during lectures.
3.1 Possible Commands in the Input File
There are three legit commands:
• BUY art id art type art name artist name price
• UPDATE art id art type art name artist name price
• SELL art id price
3.2 Requirements to the Input Format
General rule is that everything that is not correct is incorrect.
There are several requirements for the input formats including flags:
• Art piece ID is an integer number greater than zero.
• Art type is one word of up to 10 letters in size.
• Art name can consist only of letters and spaces and its size is from 3 to
50 letters inclusive.
• Artist name can consist only of letters and spaces and its size is from 3 to
20 letters inclusive.
• Price is an integer number greater than zero.
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3.3 Output Format
Output format for the art piece record is the following:
ID TYPE ART-NAME ARTIST-NAME PRICE
And they all separated by white space, for example,
15 PAINTING Girl on the ball Picasso 100
If you have more than one art piece record to print then just print each
record on a new line. Format for each record should look like
“%d %s %s %s %d”
After all records you also should print available budget and worth of the art
in the collection.
3.4 Errors/No Student Records to Print
As you shall not rely on neither user providing the correct combination of flags
nor the input file being correct, you always should check for possible errors. In
this assignment we provide list of some errors that you need to check with print
statement that should be printed.
• NO QUERY PROVIDED if application executed without flags.
• FILE EXISTS see flag “-o” description.
• FAILED TO PARSE FILE if something wrong with one of the fields
in the input file or there is an unknown command.
• ID NOT UNIQUE if trying to add a record with ID that already exists
in the database.
• RECORD CANNOT BE DELETED NOR UPDATED if trying
to delete a record that does not exist or trying to update a record by given
ID that does not exist.
• RECORD NOT FOUND if flags were legit but there is no such record
in the database.
• NOT ENOUGH MONIES if there is not enough monies in the budget
to buy the next art piece.
• OTHER ERROR when there is an error but not within above categories.
3.5 Linked List
As stated in the assignment, you should use linked list to store are pieces records
and later retrieve information about them. Moreover, elements in the list should
be sorted in ascending order by art piece ID. It means that if element A of the
list points to element B in the list (or you can say A goes before B in the list)
then art piece ID stored in the A should be less than art piece ID stored in the
B. It also implies that you cannot just append new records to the end of list.
Sometimes you will need to insert them somewhere in the middle of the list.
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3.6 Actual programming task
Now, as you are familiar with all the separate pieces of the application let’s put
all of them together. The user runs the application user following command:
$ a r t c o l l e c t o r fil e n am e −b N [−v ] [− i i d ]
[−t type ] [−n a r ti s t n am e ] [−o fil e n am e ]
The first parameter is the name of the input file and it is a mandatory
parameter. It is safe to assume that it always comes as a first parameter.
Another mandatory parameter is a budget. It indicates the initial amount of
monies the art collector has, which later will be used to “buy” art pieces.
The next step is to parse the input file. Every time you encounter the “BUY”
command you need to check if there is enough budget to purchase the art piece,
add it to the database, and update the remaining budget accordingly. If it the
“UPDATE” command then you need to update that particular art piece, e.g.
the command may update the price that will affect art collection worth. Finally,
if it “SELL” command then you need to remove art piece from the database
and update the budget accordingly. Please note that you need to parse file
line-by-line. It means that if the there is not enough monies to purchase the
next art piece then you need to print corresponding error message and exit the
program.
After file parsing is complete you need to print the records in database and
print remaining budget and art collection worth, which is the sum or prices of
every art piece in the database.
Important to note, that we will compile your program using make command.
We provide useful material for the Makefile and make command in the readings
sections.
3.7 Extra Credit
There are two possibilities for extra credit.
3.7.1 Maximizing art collection worth
In the homework you need to parse the input file line-by-line. It means that if
you encounter the art piece with the price higher that currently available budget
you should print the error message and exit the program. However, in this extra
credit part of the assignment you need to ignore such fact and purchase all the
art pieces from the database that will maximize the art collection worth.
3.7.2 Persistent database
As you may notice, every time we start the the application its internal memory
database is empty. In this extra credit part of the assignment you need to create
a persistent database. It means that the database should have records from the
previous run. For example, if the database had records A, B, and C at the end
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of the previous run then if we run your application again, these records should
be in the database.
4 GitHub Repository and Code
Please use the same GitHub account that you have created for the HW#0. Once
you are ready, please follow the link:
https://classroom.github.com/a/KxVqoQKX
which should create you a repository for this homework.
5 Useful Reading
In class we discussed that main() function can also take arguments. You can
find a bit more information and see example under the following link:
http://crasseux.com/books/ctutorial/argc-and-argv.html
On top of that, we discussed that there is a better way to deal with flags.
More specifically, using getopt() function. More information is available under
the following link:
https://www.gnu.org/software/libc/manual/html_node/Getopt.html
Next three following link provide information on the Makefile:
http://mrbook.org/blog/tutorials/make
http://www.cs.colby.edu/maxwell/courses/tutorials/maketutor
https://www.tutorialspoint.com/makefile/index.htm
The following link were mentioned in the text earlier:
https://www.iterm2.com
PuTTY instructions
http://smartty.sysprogs.com
https://en.wikipedia.org/wiki/Secure_Shell
http://blog.robertelder.org/what-is-ssh
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