blog/c/pexam/c-cams.md

slug	title	description	last_update
cams	Practice exam C	Stalking cars…	date 2023-05-07

Watching Cams

:::caution Exam environment

• During the exam you will be provided with a barebone exam session on the faculty computers.
• In browser you are only allowed to have the following tabs open:
  • C documentation
  • page containing the assignment
• You are not allowed to use your own source code, e.g. prepared beforehand or from the seminars.
• You have 5 minutes to read through the assignment and ask any follow-up questions should be there something unclear.
• You have 60 minutes to work on the assignment, afterward your work will be discussed with your seminar tutor.

:::

Your task is to write a program cams that will be processing input from the cams that are capable of identifying license plates on the cars and then print out summary based on the input data. Your contributions to the society are very much appreciated and may (or may not) be used for (each or none) of the following purposes¹:

• stalking people leaving and coming back home,
• retroactively making people pay for the parking,
• providing evidence of people speeding on highways,
• tracking people that don't pay tolls, or
• convict employees leaving the work prematurely.

Format of the input file

Input for your program consists of the data from the cameras. You will be given the data from the cameras as a path to a file and user should also be able to specify - (i.e. stdin) as the path.

Each “scan” (i.e. reading) of the cameras consists of the following data:

• camera ID: non-negative integer identifying a camera

• plate: string of unknown length that can consist of any characters apart from whitespace

• timestamp: date and time of the scan as an unsigned integer (represented as a UNIX time)

  :::tip

  When programming on UN*X(-like) systems, you can assume that the time_t structure from the system header time.h is the unsigned int that you are provided in the input file.

  :::

And they are compiled into one reading such as:

camera_ID: plate timestamp

There should be always at least one space in between each part of the reading. Readings are separated by the commas, which may, but don't have to, be accompanied by whitespace around.

Examples

Few examples of the data from the cameras follow

10: ABC-12-34 1664608712, 289: XYZ-98-76         1665416417,
25: ABC-12-34   1633078256  , 42: TryToCatchMe 1671602419,
11: EL9-987 1679541338 ,2 :  Foo-666 1683170082,42: YourMum 1683170082,
42: TryToCatchMe 1671602419   ,    1234: TryToCatchMe 1671602419,
19: ABC-12-34 1664659649, 69:YouShould-not-pLaCe-4ny-expectations%on^the(input 1680307994,
9 : 9B9-161 1665416417     , 10: 1a1-999 1671602419,1:lmao 1633078256,
16: ABC-12-34 1664609012

Format of the output

:::info

All the examples consider using data from the example of the input.

:::

You are expected to print out the dates and cameras that has captured the license plate for each of them (in a sorted fashion).

If there are multiple scans present and the timespan (i.e. time difference between the scans is bigger than 60 minutes, you should separate them by a newline). For example:

*** ABC-12-34 ***
   25: Fri Oct  1 10:50:56 2021

   10: Sat Oct  1 09:18:32 2022
   16: Sat Oct  1 09:23:32 2022

   19: Sat Oct  1 23:27:29 2022

:::tip

Since you are given the timestamp in a time_t compatible type on UN*X, you can safely use ctime(3) for printing the timestamp as a human readable time when outputting the date and time.

:::

:::tip

For a better readability you can include one more newline after the last line of the output.

:::

Example usage

You can also have a look at example usage of your program. We can run your program from the shell like

$ ./cams example_1.txt

And it will produce an output:

*** ABC-12-34 ***
   25: Fri Oct  1 10:50:56 2021

   10: Sat Oct  1 09:18:32 2022
   16: Sat Oct  1 09:23:32 2022

   19: Sat Oct  1 23:27:29 2022

*** EL9-987 ***
   11: Thu Mar 23 04:15:38 2023

*** Foo-666 ***
   2: Thu May  4 05:14:42 2023

*** TryToCatchMe ***
   42: Wed Dec 21 07:00:19 2022
   42: Wed Dec 21 07:00:19 2022
   1234: Wed Dec 21 07:00:19 2022

*** XYZ-98-76 ***
   289: Mon Oct 10 17:40:17 2022

*** YouShould-not-pLaCe-4ny-expectations%on^the(input ***
   69: Sat Apr  1 02:13:14 2023

*** YourMum ***
   42: Thu May  4 05:14:42 2023

Requirements and notes

• Define structures (and enumerations, if applicable) for the parsed information from the files.
• For keeping the “records”, use some dynamic data structure.
  • Don't forget to consider pros and cons of using specific data structures before going through implementing.
• You are not required to produce 1:1 output to the provided examples, they are just a hint to not waste your time tinkering with a user experience.
• If any of the operations on the input files should fail, you are expected to handle the situation accordingly.
• Failures of any other common functions (e.g. functions used for memory management) should be handled in the same way as they were in the homeworks and seminars.
• Your program must free all the resources before exiting.

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1. Subject to NDA. ↩︎