Week 09 Laboratory Exercises
Objectives
- learning how to retrieve environment variables
- learning how to access file metadata via stat
- learning how to use file metadata
- practicing file operations generally
- understand make's core operation
Preparation
Before the lab you should re-read the relevant lecture slides and their accompanying examples.
Getting Started
lab09 and changing to this directory.
mkdir lab09 cd lab09
There are some provided files for this lab which you can fetch with this command:
1521 fetch lab09
If you're not working at CSE, you can download the provided files as a zip file or a tar file.
Exercise — individual:
Print Select Bytes from a File
Write a C program, print_select_bytes.c, which is given a filename and one or more positions as command line arguments.
It should print the byte that is located at each given position within the file.
It should print each byte in decimal, two digit hex, and (if possible) the character itself.
Follow the output format below.
Do not read the entire file - use fseek(3) to move around the file.
dcc print_select_bytes.c -o print_select_bytes ./print_select_bytes lorem-ipsum.txt 0 1 2 3 4 76 - 0x4C - 'L' 111 - 0x6F - 'o' 114 - 0x72 - 'r' 101 - 0x65 - 'e' 109 - 0x6D - 'm' ./print_select_bytes lorem-ipsum.txt 542 361 840 232 97 546 1612 2508 96 85 1382 116 - 0x74 - 't' 101 - 0x65 - 'e' 117 - 0x75 - 'u' 10 - 0x0A 101 - 0x65 - 'e' 108 - 0x6C - 'l' 32 - 0x20 - ' ' 111 - 0x6F - 'o' 116 - 0x74 - 't' 114 - 0x72 - 'r' 116 - 0x74 - 't'
When you think your program is working,
you can use autotest
to run some simple automated tests:
1521 autotest print_select_bytes
When you are finished working on this exercise,
you must
submit your work by running give:
give cs1521 lab09_print_select_bytes print_select_bytes.c
You must run give
before Monday 29 July 12:00 (midday) (2024-07-29 12:00:00)
to obtain the marks for this lab exercise.
Note that this is an individual exercise,
the work you submit with give must be entirely your own.
Exercise — individual:
Find the First Invalid UTF-8 Byte
You have been given invalid_utf8_byte.c,
which contains a C function invalid_utf8_byte,
that takes a string and returns 42.
Add code to the function invalid_utf8_byte so that,
given a string containing one or more invalid UTF-8 sequences,
it returns the index of the first unexpected byte in the string,
and -1 if the string if the string contains no invalid UTF-8 sequences.
For example:
unzip invalid_utf8_byte_examples.zip (several lines of output) xxd invalid_utf8_byte_examples/hello_world.txt 00000000: 6865 6c6c 6f20 776f 726c 64 hello world ./invalid_utf8_byte < invalid_utf8_byte_examples/hello_world.txt No invalid bytes found. xxd invalid_utf8_byte_examples/bad_hello_world.txt 00000000: 6865 6c6c 6fa1 776f 726c 64 hello.world ./invalid_utf8_byte < invalid_utf8_byte_examples/bad_hello_world.txt Invalid byte found at index 5. xxd invalid_utf8_byte_examples/too_few_continuation_bytes.txt 00000000: f09f 98 ... ./invalid_utf8_byte < invalid_utf8_byte_examples/too_few_continuation_bytes.txt Invalid byte found at index 3. xxd invalid_utf8_byte_examples/too_many_continuation_bytes.txt 00000000: f09f 98b3 98 ..... ./invalid_utf8_byte < invalid_utf8_byte_examples/too_many_continuation_bytes.txt Invalid byte found at index 4. xxd invalid_utf8_byte_examples/valid_with_emoji.txt 00000000: 796f 7520 6172 6520 646f 696e 6720 6772 you are doing gr 00000010: 6561 7420 f09f 918d f09f 918d f09f 918d eat ............ ./invalid_utf8_byte < invalid_utf8_byte_examples/valid_with_emoji.txt No invalid bytes found. xxd invalid_utf8_byte_examples/invalid_with_emoji.txt 00000000: 7468 6973 f0a1 3923 7374 7269 6e67 a269 this..9#string.i 00000010: 73e7 8936 6e6f 74a0 646f 696e 67c2 c273 s..6not.doing..s 00000020: 6fa0 6772 6561 74f1 3242 a068 6f77 6576 o.great.2B.howev 00000030: 6572 20f0 9f98 ad91 er ..... ./invalid_utf8_byte < invalid_utf8_byte_examples/invalid_with_emoji.txt Invalid byte found at index 6.Further example inputs are provided in the
invalid_utf8_byte_examples.zip archive.
When you think your program is working,
you can use autotest
to run some simple automated tests:
1521 autotest invalid_utf8_byte
When you are finished working on this exercise,
you must
submit your work by running give:
give cs1521 lab09_invalid_utf8_byte invalid_utf8_byte.c
You must run give
before Monday 29 July 12:00 (midday) (2024-07-29 12:00:00)
to obtain the marks for this lab exercise.
Note that this is an individual exercise,
the work you submit with give must be entirely your own.
Exercise — individual:
Append to a Diary File
$HOME/.diary
Write a C program, diary.c, which appends 1 line to $HOME/.diary.
The line should be its command-line arguments separated by a space followed by a '\n'.
$HOME represents the HOME environment variable. This means you will need to retrieve
the value of the environment variable, join it with the name of the file we wish to open and then use the resulting
pathname in order to open it.
diary.c should print nothing on stdout. It should only append to $HOME/.diary.
dcc diary.c -o diary ./diary Lisa cat $HOME/.diary Lisa ./diary in this house ./diary we obey the laws of thermodynamics cat $HOME/.diary Lisa in this house we obey the laws of thermodynamics
When you think your program is working,
you can use autotest
to run some simple automated tests:
1521 autotest diary
When you are finished working on this exercise,
you must
submit your work by running give:
give cs1521 lab09_diary diary.c
You must run give
before Monday 29 July 12:00 (midday) (2024-07-29 12:00:00)
to obtain the marks for this lab exercise.
Note that this is an individual exercise,
the work you submit with give must be entirely your own.
Challenge Exercise — individual:
ls -ld
Write a C program, lsld.c, which is given zero or more pathnames as command line arguments
produces exactly the same output as ls -ld given the same pathnames as arguments.
Except ls -ld sorts its output lines. You do not have to match this.
You should exactly match the output format of ls -ld. An example follows, although your output will depend on the metadata associated with the arguments that your provide.
dcc lsld.c -o lsld mkdir -m 751 -p test_dir ls -ld test_dir invalid_utf8_byte_examples/hello_world.txt invalid_utf8_byte_examples lsld.c /home/cs1521/public_html drwxr-x--x 38 cs1521 cs1521 4096 May 30 19:26 /home/cs1521/public_html drwxr-xr-x 2 z5555555 z5555555 4096 Apr 10 2023 invalid_utf8_byte_examples -rw-r--r-- 1 z5555555 z5555555 11 Apr 10 2023 invalid_utf8_byte_examples/hello_world.txt -rw-r----- 1 z5555555 z5555555 1521 Jul 10 11:51 lsld.c drwxr-x--x 2 z5555555 z5555555 4096 Jul 10 11:44 test_dir ./lsld test_dir invalid_utf8_byte_examples/hello_world.txt invalid_utf8_byte_examples lsld.c /home/cs1521/public_html drwxr-x--x 38 cs1521 cs1521 4096 May 30 19:26 /home/cs1521/public_html drwxr-xr-x 2 z5555555 z5555555 4096 Apr 10 2023 invalid_utf8_byte_examples -rw-r--r-- 1 z5555555 z5555555 11 Apr 10 2023 invalid_utf8_byte_examples/hello_world.txt -rw-r----- 1 z5555555 z5555555 1521 Jul 10 11:51 lsld.c drwxr-x--x 2 z5555555 z5555555 4096 Jul 10 11:44 test_dir
When you think your program is working,
you can use autotest
to run some simple automated tests:
1521 autotest lsld
When you are finished working on this exercise,
you must
submit your work by running give:
give cs1521 lab09_lsld lsld.c
You must run give
before Monday 29 July 12:00 (midday) (2024-07-29 12:00:00)
to obtain the marks for this lab exercise.
Note that this is an individual exercise,
the work you submit with give must be entirely your own.
Submission
give.
You can run give multiple times.
Only your last submission will be marked.
Don't submit any exercises you haven't attempted.
If you are working at home, you may find it more convenient to upload your work via give's web interface.
Remember you have until Week 10 Monday 12:00:00 (midday) to submit your work without receiving a late penalty.
You cannot obtain marks by e-mailing your code to tutors or lecturers.
You check the files you have submitted here.
Automarking will be run by the lecturer several days after the submission deadline,
using test cases different to those autotest runs for you.
(Hint: do your own testing as well as running autotest.)
After automarking is run by the lecturer you can view your results here. The resulting mark will also be available via give's web interface.
Lab Marks
When all components of a lab are automarked you should be able to view the the marks via give's web interface or by running this command on a CSE machine:
1521 classrun -sturec