Labsheet 4: Reading from Text Files
For the week commencing Monday 25th August.
Most of the following tasks will require you to write functions that
read the contents of a text file.
Your programs will typically require the C99 functions
fopen,
fgets, and
fclose.
Refer to Lecture 4 for an example of how to do this.
Use the sample text file SampleTextFile
for testing your programs.
This week's tasks:
Remember that we're using a 
to indicate if a question is a bit more difficult.
First-time programmers should aim to complete all questions without chilies.
| 1. |
Write a function named display that displays the contents of
a text file, line-by-line.
Your function should take one argument, a character array that represents
the name of the file to display, and should return void.
Test your function from with a program
that accepts a filename as a single command-line argument,
passing this string to your display function.
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| 2. |
The Mac-OSX system, and all Unix/Linux systems, provide a standard
command named wc (an abbreviation for wordcount!)
which determines the number of lines,
words, and characters in a named file.
You may read about this command using the online documentation:
csse2100% man wc
For this task, and the four following, you will develop your own version
of the wc program named mywc.
Firstly, write a function named counter that calculates
and returns the number of lines contained within a file.
Recall from Lecture 4 that a line in a file may be terminated by either
a newline ('\n') or a carriage-return ('\r')
character.
As in Question 1, your function should take one argument,
a character array that provides a filename.
Make your function return void.
Your counter
function should print the number of lines in the file before returning
to the calling function.
Test your function from with a program
that accepts a filename as a single command-line argument.
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| 3. |
Extend your mywc program, and the counter
function, so that it now also calculates and prints the number of
characters found in the file.
As with the standard Unix wc program, all characters (including
newline, carriage-return, and whitespace characters) should be counted.
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| 4. |
Further extend your mywc program, and the
counter function, so that it now also calculates and prints
the length of the longest line it finds in the file.
Note however, this count should not include the newline or
carriage-return character, should they be found.
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5.
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Further extend your mywc program, and the
counter function, so that it now also calculates and prints
the number of words found in the file.
In this context, a word is defined as a continuous character sequence
separated by whitespace characters.
Refer to the online documentation (man pages) to learn how the
isspace function is useful for this question.
Make sure to compare your word count against that reported by the standard
wc command.
Hint: this task is easier if your counter function
remembers whether it is inside or outside of a word at
any time.
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6.
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Modify your mywc program such that it now accepts
command-line arguments that indicate what information should be printed.
Assume the last command-line argument is the name of the file to display,
but also allow switches (which take the form -X,
where X is a character) that controls what is displayed.
For example, use the switch -c to request the character
count, the switch -l to request the line count, the switch
-w to request the word count, and the switch -m
to request the maximum line length (note that our use of -m
is different to that used in the standard wc command).
If invoked with no command-line switches, your program should display
all counts.
csse2100% ./mywc SampleTextFile
The file 'SampleTextFile' contains 434 character(s).
The file 'SampleTextFile' contains 72 word(s).
The file 'SampleTextFile' contains 12 line(s).
The longest line in the file 'SampleTextFile' contains 68 character(s).
csse2100% ./mywc -m -w SampleTextFile
The file 'SampleTextFile' contains 72 word(s).
The longest line in the file 'SampleTextFile' contains 68 character(s).
Note: the order of the switches on the command-line is irrelevant,
but they must appear before the filename.
You will need to modify your main function so that it now has
(four, if you have completed all the parts above) new Boolean variables
(named cflag, lflag, mflag,
and wflag) to indicate if the corresponding command-line
switch was seen on the command-line.
You will also need to modify your counter function so that it
now additionally accepts arguments that control which values to display.
Do this by adding Boolean arguments that are either true
or false depending on whether to display that particular
value or not.
For example, your function should look like something like:
void counter(char name[], bool displayLineCount, bool displayWordCount,
bool displayCharCount, bool displayMaxLine)
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7.
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Write a function named areFilesEqual that determines if
the contents of two text files are identical (i.e. if every character
in the first file appears in the second file in precisely the same order).
Your function should take two arguments: two character arrays that
represent the names of the files to compare, and return a Boolean
indicating whether the files are identical or not.
The calling function (the main function) should report the
result returned by your areFilesEqual function. Accept the
names of the files as two command-line arguments.
Do this two ways:
- Using a loop to iterate over all the characters, performing the
comparison character by character.
- Using the C99 standard
strcmp function to
compare two lines (one from each file) directly.
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| 8. |
Using Lecture 4 as a guide, write a program (and function)
named pattern to search through the Unix dictionary
(/usr/share/dict/words) for a given word.
Your function should take one argument, a character array that represents
the word to locate for in the dictionary, and prints out a message
indicating whether you found an exact match or not.
Accept, as a single command-line argument to your program, the pattern
required. For example:
csse2100% ./pattern food
pattern 'food' found in /usr/share/dict/words
csse2100% ./pattern foid
Pattern 'foid' NOT found in /usr/share/dict/words
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| 9. |
Extend your program from Question 8 such that the provided pattern
may contain a period character ('.'), meaning "match any
character".
In this context, a period means a character must be present at that
location in the word, but that character can be any character.
For example:
csse2100% ./pattern fo.d
pattern 'fo.d' found in /usr/share/dict/words: fold
pattern 'fo.d' found in /usr/share/dict/words: food
pattern 'fo.d' found in /usr/share/dict/words: ford
pattern 'fo.d' found in /usr/share/dict/words: foud
csse2100% ./pattern f...f
pattern 'f...f' found in /usr/share/dict/words: feoff
pattern 'f...f' found in /usr/share/dict/words: flaff
pattern 'f...f' found in /usr/share/dict/words: fluff
csse2100% ./pattern j...j
pattern 'j...j' NOT found in /usr/share/dict/words
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10.
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Extend your program from Question 9 such that the provided pattern may
contain an asterisk character ('*'), meaning "match zero
or more characters at this position".
In this context, an asterisk can be replaced by any number of (including
zero) other characters, all of which may be any other character.
For example:
csse2100% ./pattern 'g*o'
All words in the dictionary starting with 'g' and ending with 'o' are
printed (including the word "go")
csse2100% ./pattern '*a'
All words in the dictionary ending with 'a' are printed (including the word "a")
csse2100% ./pattern '*'
All words in the dictionary are printed.
Very hard!
csse2100% ./pattern '*al*cat*'
All words in the dictionary containing the sub-patterns "al" "cat", each
separated by zero or more characters. There are 64 of them in the
standard Macintosh dictionary.
NOTE: in the examples above, the command-line arguments containing
asterisks need to be surrounded within single quotation characters to
prevent the shell from attempting to expand them as filename patterns
(e.g. proj*t.c).
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