Operating Systems

DM510, Spring 2013

Daniel Merkle

DM510 Required Assignment 1: C-programming

(Exercise based on suggestion by Arun Vadiveal.)

In this assignment, your task is to solve a series of small programming tasks in C. For each task a file with method stubs is available. These files will help you get started, but they also serve to define the input and output of functions. The files can be downloaded here. You can unpack them with the command tar -xvf assignment1.tar. A bash script run is included to compile and run the files for each task. You may need to make the script executable with chmod u+x run. The script also includes a simple test case for each task, to help avoid misunderstandings concerning the input/output format. As a minimum your implementation must succeed in each of the simple tests. Your implementation will be tested more thoroughly with additional tests during the evaluation, thus make sure to test additional border line scenarios yourself.

Task 0: Hello World

For this task, you are given the file "helloworld.c", and need to add the necessary lines of code to make it print "Hello World" to standard out. Try compiling the file using gcc. You can type man gcc in a console to read about how to use it.

Task 1: Repeat

For this task, you are given the file "repeat.c". Your implementation must read the parameters passed to the program and write them out in the same order seperated by a single space. For instance ./repeat These are arguments. should result in the following being written to standard out: These are arguments..

Task 2: Linked List

For this task, you are given the file "llist.c". In this task you will need to know a little about pointers and structs. If you feel lost, make sure to take a look at the Online C Programming course, especially the sections: "Pointers in C" and "Structures in C".

You need to implement two functions. The first is to insert an element into a linked list: int insert( char *buffer, int index ). The parameters are a pointer to a buffer containing a message and an index for the position to insert the element in (0 results in the element being the new head, 1 means after the head, etc.). The global variable head serves as an entrypoint to the linked list. Initially the head is NULL, and the first insert is made by allocating memory for the structure and making head point to this memory location. As the content of the buffer may be changed by the caller, it is important to allocate memory for the message, copy the contents of the buffer and store the pointer to the allocated memory, instead of just using the pointer given as input. Also in C allocated memory can contain random data, so make sure to explicitly set the next-pointer to NULL. Additional inserts are done similarly, but remember to update the appropriate next-pointers such that elements are not lost.

The second function, llelem_t* extract_head( ), is a simple function that returns the current head of the linked list, while removing it from the list. Removing the head-element is done by simply referring to the next element as the new head.

Task 3: Linked List Extension

For this task, you will need a working implementation of Task 2. The purpose is to get more familiar with string manipulation in C. So if you haven't already read about strings in C, you should take a look at the Online C Programming course and also try typing man string in a console. In addition to the existing method for inserting single elements, you need to implement the function: void list_from_string( char* );. The function will insert a list of elements based on the string given as parameter. The string is considered a comma separeted list of elements, such that list_from_string( "Yoda,am,I" ) would result in the linked list with the elements: "I" -> "am" -> "Yoda". By using the already implemented method for insertion, the task is to repeatedly extract the substring up until the first comma or the '\0' character, and perform an insert( substring, 0 ).

Submitting your solution

For submitting the sources proceed as follows: Create the following directory structure


Put the sources and also the bash script run in that directory.

Before you submit your solution, make sure your output of the run script is identical to the following output:

Test 0:
Compile succeeded without warnings
output:   'Hello World' is equal to
expected: 'Hello World'
Test:     Success

Test 1:
Compile succeeded without warnings
output:   'Please repeat this.' is equal to
expected: 'Please repeat this.'
Test:     Success

Test 2:
Compile succeeded without warnings
output:   'This is a small message.' is equal to
expected: 'This is a small message.'
Test:     Success

Test 3:
Compile succeeded without warnings
output:   'Testing list from command line arguments.' is equal to
expected: 'Testing list from command line arguments.'
Test:     Success

Change to the directory assignment1 and type aflever DM510 your@mail.com.

The deadline for the 1st mandatory assignment is February 21th, 11:00 . But please note that it is quite likely the second manadtory assignment will be announced before that day.

Frequently Asked Questions (FAQ)

  • Are we allowed to work in groups?
  • No, this assignment has to be solved individually. However feel free to discuss and problems with the TA or with other students. Note, that we will perform a plagiarism check.

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