Do not start the test until instructed to do so!

Transcription

1 Instructions: Print your name in the space provided below. This examination is closed book and closed notes, aside from the permitted one-page formula sheet. No calculators or other electronic devices may be used. The use of any such device will be interpreted as an indication that you are finished with the test and your test form will be collected immediately. Answer each question in the space provided. If you need to continue an answer onto the back of a page, clearly indicate that and label the continuation with the question number. If you want partial credit, justify your answers, even when justification is not explicitly required. There are 6 questions, some with multiple parts, priced as marked. The maximum score is 100. When you have completed the test, sign the pledge at the bottom of this page and turn in the test. If you brought a fact sheet to the test, write your name on it and turn it in with the test. Note that either failing to return this test, or discussing its content with a student who has not taken it is a violation of the Honor Code. Do not start the test until instructed to do so! Name printed Pledge: On my honor, I have neither given nor received unauthorized aid on this examination. signed A 1

2 xkcd.com A 2

3 1. Suppose your current working directory is mono within the Linux directory structure shown below, list the Linux command(s) you would use to accomplish each of the following goals, in a minimal fashion. Each part is independent; i.e., you start with the initial settings shown below. src mono AzureBenchmark.cs AzureBuildRequest.cs AzureOperations.cs CFS.cs CFS.exe CVS Entries Repository Root main.c README stage client.py common.py config.pyc CVS Entries Repository Root server.py transfer.py a) [6 points] Copy all of the.py files in the stage directory that start with the letter c into the mono/cvs directory. cp../stage/c.py CVS b) [6 points] Move the README file from the mono directory to the stage directory. mv README../stage c) [6 points] Create a tar file in the src directory containing all of the.py and.pyc files in the stage directory. tar cf../anyname.tar../stage/py../stage/pyc A 3

4 2. Suppose that your user id is johokie and that a listing (ls l) of the contents of your current working directory provides the following information: [CentOS tmp 1234]$ ls l total 32 -rw-r--r-- 1 johokie academic :56 data.txt -rw-rw johokie academic :56 results.txt -rwx--x--- 1 johokie academic :50 newton -rwxr-x--x 1 johokie academic :35 raphson List the Linux command(s) you would use to accomplish each of the following goals, in a minimal fashion. That is, there should be no other rights granted or removed unless it is unavoidable. Assume the commands will be entered in the current working directory whose contents are shown above. The parts are independent; i.e., you start with the initial settings shown above. a) [6 points] Allow only the owner to read and write the contents of the file data.txt. chmod go-r data.txt chmod 600 data.txt b) [6 points] Prevent the group from executing the file newton. chmod g-x newton chmod 700 newton c) [6 points] Allow others to also read and modify the contents of the file results.txt. chmod o+rw results.txt chmod 666 result.txt A 4

5 3. Analyze the C function given below. Be sure to pay careful attention to the comments. The function is syntactically correct, but the logic of the design is not entirely valid. / Compare the contents of two integer arrays. If two arrays have the same values at the same indexes they are considered equal. Returns: 1 If contents of are the same. 0 If the contents of the array differ. Examples: A = 1, 2, 3, 4, B = 1, 2, 3, 4 would return 1 A = 1, 2, 3, 4, B = 1, 2, 4, 3 would return 0 / int arr_cmp(int A[], int B[]) int result = 0; if (A == B) result = 1; return result; a) [6 points] Explain clearly why the given implementation will not achieve the stated goals. This compares the "names", or the locations of the array rather than the contents of the arrays. b) [10 points] Write a corrected version of the function that will achieve the stated goals. You may make any changes you like including the number of arguments or return type, as long as you don't use any file-scoped variables. int arr_cmp(int A[], uint32_t ausage, int B[], uint32_t busage) int result = 1; if (ausage!= busage) result = 0; else for (uint32_t x = 0; x < ausage; x++) if (a[x]!= b[x]) result = 0; break; return result; A 5

6 4. [16 points] Implement the C function described below. Be sure to note the restrictions, violating the restrictions will result in a very low score. / Pre: "value" has an odd number of digits Returns: The "middle" digit of value. Examples: middle_digit(0) returns 0 middle_digit(1) returns 1 middle_digit(9) returns 9 middle_digit(123) returns 2 middle_digit(12345) returns 3 middle_digit( ) returns 4 Restrictions: You may not use I/O, files, arrays, or strings. / uint8_t middle_digit(uint64_t value) uint64_t temp = value; uint8_t digit_count = 0; while (temp / 10!= 0) temp = temp / 10; digit_count++; temp = value; for (int x = 0; x < digit_count/2; x++) temp = temp / 10; return temp % 10; A 6

7 5. [16 points] Implement the C function described below. / Converts and sums the integers in string "line". Unfortunately, the integers are mixed with other string data. Moreover, "line" can be any length and can contain an arbitrary number of integers (0 or more). Fortunately, there is a pattern in the string, there will always be an integer, followed by other characters that aren't numbers or whitespace, followed by space characters or the end of the string. Example: process_line("508aasd 25Casda 6689Jadas"); Will return value 7222, which is / uint32_t process_line(const char const line) int sum = 0, tot = 0, num = 0, num_bytes; while(sscanf(line + tot, "%d%s %n", &num, &num_bytes) == 1) tot += num_bytes; sum += num; return sum; A 7

8 6. [16 points] Implement a C function that will parse a limited version of the common.ini file format, printing a report like the one shown on the left below. The gray box on the right shows a sample.ini file. For the purposes of this question, there are two types of lines you'll need to process: (1) Lines that look like[ section_name ]. You'll want to grab the section_name and display it as shown below. You may assume there will always be space characters separating the square brackets and the section_name. (2) Lines that look like variable_name = value. You'll want to grab both the variable_name and the value and display them as shown below. You may assume there will always be space characters separating the variable_name, the =, and the value. Section names, variables, and values will always be single chunks of text and will not contain whitespace characters. Further, they will always be less than 256 characters. Finally, don't try to convert anything into a number, just treat everything as string. Found section: DEFAULT Variable: ServerAliveInterval, Value: 45 Variable: Compression, Value: yes Variable: CompressionLevel, Value: 9 Variable: ForwardX11, Value: yes Found section: bitbucket.org Variable: User, Value: hg [ DEFAULT ] ServerAliveInterval = 45 Compression = yes CompressionLevel = 9 ForwardX11 = yes [ bitbucket.org ] User = hg void parse_ini(const char const filename) FILE f = fopen(filename, "r"); while (fgets(line, 256, f)!= NULL) if(sscanf(line, "[ %s ]", section_name) == 1) printf("found section: %s\n", section_name); else if(sscanf(line, "%s = %s", var, value) == 2) printf("\tvariable: %s, Value: %s\n", var, value); fclose(f); A 8

9 Left Intentionally Blank Extra space for Question 6, or any other Question. A 9