ETH_Informatik/Informatik_I/Exercise_12/Task_3

Task 3: Array-based Vector, Rule of Three

• Task
• Solution

Task

You are provided a partial implementation of an array-based vector class our_vector. Declarations are given in file our_vector.h, member functions that are already implemented are in file our_vector_locked.cpp. Your task is to implement the copy constructor, assignment operator and destructor for class "our_vector", in file our_vector.cpp. Note that the vectors store values of type tracked and not int as in the lecture, but you can treat them in the same fashion; the tracked values are used behind the scenes for checking your solution.

Steps:

1. Implement the copy constructor for class our_vector so that it creates a copy of the internal array.
2. Implement the assignment operator so that it creates a copy of the provided our_vector and destroys the vector that is currently assigned to the left-hand-side of the assignment (e.g., by swapping its current contents to a local copy, as described in the lecture).
3. Implement the destructor so that it deallocates the internal array.

Memory tracking: The internal elements of class our_vector are objects of class tracked (see file tracker.h). Such objects encapsulate a single integer location which is tracked by an internal memory manager. This is used internally to catch as many memory/deallocation errors as possible upon occurrence.

Testing: Tests are already provided in file main.cpp. If you want to carry out further testing yourself, you may do so within function your_own_tests(), which is called by main() when encountering an unknown test identifier. You can edit this function in file our_vector.cpp.

Valgrind output After you implemented the copy constructor (subtask 1), you may see the following (or similar) output generated by valgrind:

Remaining tracked elements: 6

memory errors:
[ERROR:Leak_DefinitelyLost] 20 bytes in 1 blocks are definitely lost in loss record 1 of 2
in function `our_vector::our_vector(int)` at our_vector_locked.cpp:6
in function `test_copy_constructor()` at main.cpp:9
in function `main` at main.cpp:63
[ERROR:Leak_DefinitelyLost] 20 bytes in 1 blocks are definitely lost in loss record 2 of 2
in function `our_vector::our_vector(our_vector const&)` at our_vector.cpp:5
in function `test_copy_constructor()` at main.cpp:13
in function `main` at main.cpp:63

This indicates that in your program some memory has been dynamically allocated (in this case one our_vector object), but then this memory is definitely lost when the main function returns (the memory can not be longer accessed).

To solve this issue, you have to implement the object destructor (subtask 3).

Solution

#include "our_vector.h"
#include <unordered_set>

our_vector::our_vector(const our_vector &vec) /* TODO */ {
  count = vec.count;
  elements = new tracked[count];
  for (int i = 0; i < count; ++i) {
    elements[i] = vec.elements[i];
  }
}

our_vector &our_vector::operator=(const our_vector &t) {
  if (this != &t) {
    delete[] elements;

    count = t.count;
    elements = new tracked[count];

    for (int i = 0; i < count; ++i)
      elements[i] = t.elements[i];
  }
  return (*this);
}

our_vector::~our_vector() { delete[] elements; }

void your_own_tests() {
  // Any extra test here.
}

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