Department of Computer Science

Assessment of course

• The overall assessment for this course is based on 30% course work and 70% final examination.
• The 30% Coursework is one piece of practical programming in C++.

At last this is it, 2 weeks late but I've added 2 weeks to the deadline

M.Sc. in Computer Science,
Further languages coursework 2002-2003:
Login accounting

Set Date:

4th November 2002

Due Date:

Friday 13th December 2002, or if that is unlucky Thursday 12th December 2002

Time Required:

20 hours

Value:

100% of referred in-course assessment (30% of total)

Lecturers:

Bob Dickerson & Daniel Polani

Assessed objectives (from front cover)

• The student will be able to program in a commonly used programming language (fully)
• Understand the main components of programming languages and how they vary (partly)

Task

Design, write and test a program in C++ to calculate total usage times per user from a file of login and logout records. Every time a user logs into a Unix workstation or server the login and subsequent log-out are recorded by single records in a logfile. Periodically (every few days or months) administrators might print a summary of the contents of the ever-growing logfile. The coursework is a program to produce such a summary from a simplified version of the logfile.

Each record (line) in the file has 4 fields: (i) the terminal or network line on which a login occurs, (ii) the user name, (iii) the time of the login expressed as the number of seconds since the 1st January 1970, and (iv) the name of the remote system that the user logged in from, this is only used for log in records. There are four different sorts of record:

• a login record with a line name, a user name, a time, and a remote system name,
• a logout record with a line name and time but the user name is a ``~'' (tilde), the remote system name will be ``~'',
• a shutdown record where the machine crashed or was shutdown, in this case the user name is ``shutdown'' and the line name is ``~'' (tilde); the remote system name will be ``~''.

The program must match a login record to a later logout using the terminal or network line name. If a shut-down occurs all users that were logged in at the time should be accounted from their login time upto the time of the shutdown (similarly at the end of the file). The names (or the number) of the users is not known in advance nor are the terminal line names.

Any logouts without corresponding logins should be reported as errors, as should multiple logins on the same line without an intervening logout. When the file has been read the output should be a report the accumulated times in hours and minutes for each user, followed by a list of all the different remote systems each user has logged in from. As an example, given the input file of login and logout records:

  tty4        bob 807144000 wink.feis.herts.ac.uk
  tty2       root 807145199 localhost
  tty1     dumble 807145220 localhost
  tty3      polly 807145371 sally.dyn.dhs.org
  tty2          ~ 807145396 ~
  tty2        bob 807145407 localhost
  tty4          ~ 807147600 ~
  tty2          ~ 807148006 ~
  tty3          ~ 807148016 ~
  tty1          ~ 807148024 ~
     ~   shutdown 807148033 ~
  tty1        bob 807229953 tink.feis.herts.ac.uk
  tty1          ~ 807232512 ~
     ~   shutdown 807232520 ~
  tty1        bob 808521163 localhost
     ~   shutdown 808531067 ~
  tty1        bob 813449411 wink.feis.herts.ac.uk
  tty2       root 813451675 localhost
  tty3      polly 813451684 sally.dyn.dhs.org
  tty4     dumble 813451881 sally.dyn.dhs.org
  tty4          ~ 813451882 ~
  tty4     dumble 813451937 sally.dyn.dhs.org
  tty2          ~ 813452021 ~
  tty3          ~ 813452026 ~
  tty4          ~ 813452031 ~

possible program output could be:

  User totals:
  =============
  root 0:9
  bob 5:54
  polly 0:49
  dumble 0:48
  
  Remote systems used:
  ===================
  bob wink.feis.herts.ac.uk
  root localhost
  dumble localhost
  polly sally.dyn.dhs.org
  bob localhost
  bob tink.feis.herts.ac.uk
  dumble sally.dyn.dhs.org

NB (i) the time for bob might be different depending on how you deal with users still logged in at the end of the input file, and (ii) the table of remote systems used just lists each remote system used by each user, so although root logged in from localhost twice it is only reported once.

Hand in:

Hand in:

• suitably commented listings of the completed program,
• test plan for the whole program (no separate component tests), Hint: use different small test files to test different program features.

Marks awarded for: (from frontpage)

The assessment will be based on:

• the overall design and choice of objects (hint: there should probably be at least three main objects, one for outstanding logins, one for remote systems used, and one for user totals; please use encapsulation, I don't want to see any important arrays in the main program--they should be in classes. It might be simpler to use three separate, non-nested objects to record total user times and the distinct remote systems used by each user because in one case there is only one entry per user and in the other there might be more than one entry per user),
  (8 marks)
• the quality and appropriateness of the use of C++, in particular the classes, their interfaces, their constructors, scope rules etc. (hint: there is no obvious need for inheritance but you can use it if you think it is justified),
  (6 marks)
• the division of the program into separate files,
  (2 marks)
• the layout, commenting and presentation,
  (3 marks)
• how well the program meets its specification in dealing with the first 3 record types. Also note that any performance required by this program can easily be achieved by using arrays (suitably encapsulated!) rather than by any dynamic linked storage.
  (8 marks)
• the test plan and the testing. Only attempt whole program testing (do not hand in tests for program components). It is better to produce small files to test specific functionality rather than one large file that tries to test everything.
  (3 marks)

File reading hints

In order to open and read the data file you will need to read the section of the C++ notes on file I/O. But here is an example that will read one line of the file at a time on each loop iteration:

#include <cstdlib>
#include <string>
#include <iostream>
#include <fstream>

using namespace std;

int main() {
    ifstream infile;
    string line, name, remotesys;
    unsigned int time;

    infile.open("logrecs.dat");

    while(infile >> line >> name >> time >> remotesys) {
        cout << line << " " << name << " "
             << time << " " << remotesys << "\n";
    }
}

Hint: this is an adequate framework structure for the top-level of the application, just replace the output statement by a nested if to select which operations to invoke on the main objects, for login-tracking, toylas and remote systems. The best way to process the file is to deal with the input record by record (ie. don't read and store the whole lot and process them at the end). After the loop has processed the input, just invoke operations in the objects to print the results.

Page generated: 2002-11-04 by Bob Dickerson

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