CSCI-20 Assignment #4, threaded trees, 250 points, due 5/19/16
Your assignment is to model a UNIX-like file system using a threaded tree. This UNIX-like file system
has two types of nodes, directories and files. Directories contain other directories or files, represented by
the children of the directory node. Files do not contain other files, so files are always leaf nodes.
The file system begins with a single directory node, the root, which has the name "/" (slash). The root is
its own parent, so its thread points to itself. All other nodes in the system will be children, grandchildren,
etc. of the root node. Until changed by a chdir command, the current working directory (cwd) will be the
root.
Your program will support the following commands:
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mkdir name – make a new directory in the cwd with this name, if not a duplicate
rmdir name – remove the directory with this name, and all its descendants, if legal
chdir name – change cwd to the one indicated by name, if legal
support ".." for parent, "." for self, and "/" for root
or an absolute or relative path
ls – list all files and directories in the cwd
lsr – recursively list all file in this and all subdirectories
mkfile name – create a new file with this name in the cwd, if legal
rmfile name – delete the file with this name in the cwd, if legal
pwd – print the full path from the root to the cwd
Q – quit
Just represent files by their name and type, so ordinary files (non-directories) will contain no data.
Your program must take its input and output file names from the command line, and validate all
initialization before running. You will process input until either end-of-file or you encounter a 'Q'
command. After encountering the 'Q', change directory to the root and execute a pwd command and an
lsr command.
Your output is an audit of everything the program does. Thus, you should be able to completely recreate
the input file from the output audit. Your output will also show the effect of each command in the input
file. On any command failure, log a message to output that fully explains the failure.
You must check for errors in the input, for example:
 you cannot mkdir or mkfile a directory or file if the name exists already in the cwd
 you cannot rmdir or rmfile a directory or file if the name doesn't exist in the cwd
 you cannot chdir to a file
 you cannot rmfile a directory or a non-existent file
You may (will) find other problems that you also need to check for. This program needs to be robust.
Keep the file and directory names in each directory in ascending lexicographic order. If you wish, you
may keep directories and files in separate groups in the list of children, directories first and then files,
rather than intermingled.
lsr should do a recursive call to itself whenever it encounters a directory in its search. You should
indent the output from each level by three spaces for each level of recursion (no indenting spaces the
original call). Hint: make lsr a wrapper around a helper that takes the level of nesting, starting at 0.
pwd prints the entire path from root to the cwd with slashes before (for the root) between and after the
names, e.g., if usr, bin and sys are nested directories in the root, and you encounter pwd while sys is the
cwd, you will print this:
/usr/bin/sys/
chdir must move you to a legal directory, or fail completely and leave you in the same directory.
rmdir must correctly remove all files and subdirectories along with their contents.
I wrote this in about 580 lines of code, in about six hours. I expect it to take you more, both time and line
of code. Start early and design fully before you write code or you'll never finish this!
Do a test with my test file (fileTest.txt), which is on my Web site, and some with your own data
files. Include at least two of your own test files, at least one of which creates at least a four-level file
system and 25 files spread throughout the file system (all directories have at least one file) and which
does an lsr command from the root directory before quitting. Use reasonable names for the files so I
can tell which data file goes with which output.
Again, a full design, before you write any code, is going to be critical for this. If you don't solve this
first, then code afterwards, you will not be able to make this work.
The interface to a data structure is keys and objects. The interface from the client to the class that
implements the file system is commands and argument strings. This says you need to separate the data
structure from the command interface. You may do this with a nested class for the data structure, or with
an internal data structure controlled by the code to the file system class. You may do this in a couple of
different ways, but the client needs to be able to have a command interface, not a key/object interface to
the file system.