Description
Purpose
This assignment is meant to give students practice working on projects that contain multiple source code
files. It will require the students to construct a Makefile and appropriate header files. It will also require the
use of getopt to handle command line options, and manipulation of data read in from a file.
You must use read (2) for all input and write (2) for all output (excluding error messages, for which you
may use perror and/or the cerr stream object). The use of getopt (3) is not required but is strongly recommended.
Description
For this assignment, you will take the cat program you wrote for the last assignment and upgrade it to add
more features. We will call it dog instead of cat, because dogs are kind of like cats, but way better. These
new features will include:
▶ The ability to change the size of the buffer used for calls to read and write to N bytes when passed the
command line option (-s N).
▶ The ability to change the number of bytes read from each file before finishing to N when supplied with
the command line option (-n N). This is instead of reading the whole file as we would have without this
option.
▶ The ability to apply a Caesar cipher with a shift of k letters to alphabetical characters in the data read
in before writing the results when it receives the command line option (-c k).
▶ The ability to apply a general rotation (Caesar shift for all characters, not just letters) with a shift of k
to the input data before writing it back out when supplied with the command line option (-r k).
▶ The ability to output the data from the file in hexadecimal format when supplied the command line
option (-x).
▶ The ability to output the data from the file in binary notation, most significant bit first, when supplied
the command line option (-b)
Requirements
▶ The main loop should be in your main function in one source code file. The functions that process the
data (Caesar cipher/binary/hex/rotation) should be found in another file. Their declarations will need
to be in a header file, so that they can be called from main even though they will be implemented in
that other file.
▶ You must make a Makefile that has rules sufficient to compile your program when a user types make in
the same directory as your source code. Only files that have changed or that have had their dependencies change should be recompiled.
▶ You must use the system calls read for the input from the files and write for the output. You may use
cerr and perror to display error messages, but cout is disallowed, as are printf and fprintf, for the
output data.
▶ Obviously, your source code must be well documented. If it is not, there will be a large point penalty.
This requirement holds for all coding assignments in this course, whether this line is in the description
of the assignment or not.
▶ The features enabled by the command line options listed in the description section above must be
implemented.
CSCI 330 Assignment 5 (Spring 2021) 2 of 4
▶ Note: If both -r and -c are specified, the behavior can change depending on which is executed
first. Don’t allow a user to specify both. Give them an error message and exit if they try.
▶ Also: Binary and hexadecimal notation flags are mutually exclusive, as it would not be possible to
represent the data as both simultaneously. If both binary and hexadecimal modes are specified, it
is an error. Print a warning and quit.
▶ The other command line parameters can all be on at the same time without any problem. Make
sure that they work together.
▶ If no command line options are specified, this program should behave the same as cat would have, as
was specified in the previous program.
Caesar cipher
A Caesar cipher is a very primitive method of encrypting text data. It involves taking the letters of the input
and shifting them upwards alphabetically by some number of letters. This number is given as the option
parameter in the command line option that turns on the Caesar shift. If that parameter was not an integer,
do not perform any shift. Only letters (uppercase and lowercase) should have any shift applied at all. Leave
any other characters untouched. You should assume the files are using the ASCII encoding for this purpose.
(man 7 ascii).
Caesar Shift of 1 Caesar Shift of 2
a b c … x y z
a b c … x y z
a b c … x y z
b c d … y z a
a b c … x y z
a b c … x y z
a b c … x y z
c d e … z a b
Figure 1: A diagram of the basic Caesar shift cipher for shifts of one and two.
Binary rotation
While the Caesar cipher above was interpreting the bytes that you read as text, changing only alphabetical
characters, this option should apply to any value, alphabetical or not. The principle is the same, but instead
of applying it to A-Z and a-z, it is applied to each one-byte value interpreted as 0-255.
Hexadecimal representation
All numbers are stored as collections of binary bits on the computer. A char is one byte long, which is eight
bits. When dealing with files that are not meant to be read by a human (binary mode as opposed to text
mode), it can be convenient to encode the data in a format called hexadecimal.
Hexadecimal, the base-16 number system, is useful because it is based on a power of 2 (2
4 = 16), and so each
hexadecimal digit represents 4 bits. Numbers represented as decimal (base-10) do not line up in the same
way, so it can be hard to know which bits are on and which are off.
Each byte is composed of eight bits, and can be represented as two hex digits. Your program should be able
to output the data in this format (2 hex digits per input byte) whenever the -x command line parameter is
enabled. Keep in mind that there will be two characters of output for every character of input in this mode.
Since you are not allowed to use cout for the output, you won’t be able to use the hex IO manipulator to
accomplish this. Likewise, functions from the printf family using a format of %x are not permitted either.
CSCI 330 Assignment 5 (Spring 2021) 3 of 4
Hint: You can use the bitwise operators in C++ (&, |) to isolate the high order 4 bits from the low order 4 bits
in a byte, and the bitshift operators (>>, <<) can make the high order ones easier to deal with.
27 26 25 24 23 22 21 20
27 26 25 24 23 22 21 20
24*23 24*22 24*21 24*20
20 * 0-F
24 * 23 22 21 20
24 * 0-F
24*[0-F] 20*[0-F]
0-255
Decimal Hex Binary
0 0 0000
1 1 0001
2 2 0010
3 3 0011
4 4 0100
5 5 0101
6 6 0110
7 7 0111
8 8 1000
9 9 1001
10 A 1010
11 B 1011
12 C 1100
13 D 1101
14 E 1110
15 F 1111
Figure 2: A diagram illustrating how the bits of a byte can be represented in hexadecimal notation.
Binary representation
value = 128𝑏7 + 64𝑏6 + 32𝑏5 + 16𝑏4 + 8𝑏3 + 4𝑏2 + 2𝑏1 + 1𝑏0 =
7
∑
𝑖=0
2
𝑖
𝑏𝑖
Every byte is made up of eight bits, 𝑏0
to 𝑏7
, each of which is true (1) or false (0). When interpreting them as
an unsigned number, each bit, 𝑏𝑖
, answers the question of whether 2
𝑖
should be added into the sum making
up the number represented. When you output the data in binary format, you will output a 1 if the bit is true,
or a 0 if the bit is false, for all eight bits, starting from the most significant one (𝑏7
, which represents 128).
Notice that the output data will be eight times longer than the input data.
Some examples of output
% cat file1
Hello World
% ./dog file1
Hello World
% ./dog -n 5 file1
Hello
% ./dog -n 5 -c 1 file1
Ifmmp
% ./dog -n 5 -x file1
65486c6c6f
% ./dog -n 5 -b file1
0110010101001000011011000110110001101111
CSCI 330 Assignment 5 (Spring 2021) 4 of 4
What to turn in?
Submit, through Blackboard, the following files:
▶ The C++ source file (.cc) containing your main function and no others.
▶ The C++ source file (.cc) containing the functions implementing the new features added.
▶ A C++ header file (.h) containing the declarations for each of the functions implementing the new
features.
▶ A Makefile that will compile your program. The rules should be set up so that only the files that have
changed need to be recompiled.
Remember, there is no credit for late work.