Exercise 12

Added Exercise 12 to Repo

Informatik_I/Exercise_12/Task_1/README.org

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+#+TITLE: Task 1: Operator delete
+#+AUTHOR: JirR02
+
+/This task is a text based task. You do not need to write any program/C++ file: the answer should be written in main.md (and might include code fragments if questions ask for them)./
+
+* Task
+
+  All the following code fragments use operator delete and delete[] to deallocate memory, but not appropriately. This can lead to an error (including undefined behaviour) or to a memory leak. Find the mistake in each code fragment, explain whether it results in a memory leak or an error, and in the case of an error, point out the location at which it occurs.
+
+  #+BEGIN_src cpp
+  class A {
+  public:
+    A(int sz) {
+      ptr = new int[sz];
+    }
+    ~A() {
+      delete ptr;
+    }
+    /* copy constructor, assigmnent operator, public methods. */
+    ...
+  private:
+    int* ptr;
+  };
+  #+END_src
+
+  #+BEGIN_src cpp
+  struct lnode {
+    int value;
+    lnode* next;
+  };
+
+  void recursive_delete_linked_list(lnode* n) {
+    if (n != nullptr) {
+      delete n;
+      recursive_delete_linked_list(n->next);
+    }
+  }
+  #+END_src
+
+  #+BEGIN_src cpp
+  class A {
+  public:
+    A() {
+      c = new Cell;
+      c->subcell = new int(0);
+    }
+    ~A() {
+      delete c;
+    }
+    /* copy constructor, assignment operator, public methods */
+    ...
+  private:
+    struct Cell {
+      int* subcell;
+    };
+    Cell* c;
+  };
+  #+END_src
+
+  #+BEGIN_src cpp
+  void do_something(int* p) {
+    /* Do something */
+    ...
+  }
+  void f() {
+    int v;
+    int* w = &v;
+    do_something(w);
+    delete w;
+  }
+  #+END_src
+
+  #+BEGIN_src cpp
+  class Vec {
+  public:
+    Vec(int size) {
+      array = new int[size];
+    }
+    ~Vec() {
+      delete[] array;
+    }
+    int& operator[](int idx) {
+      return array[idx];
+    }
+    /* copy constructor, assignment operator, other public methods */
+    ...
+  private:
+    int* array;
+  };
+
+  void f() {
+    Vec v(5);
+    delete[] &v[0];
+  }
+  #+END_src
+
+* Solution
+
+  #+BEGIN_src md
+  1. Mistake: The mistake is that `delete` was used instead of `delete[]`
+
+     Nature: "error (undefined behaviour)"
+
+     Error location (if applicable): The mistake happens when the deconstructor `~A()` is called.
+
+  2. Mistake: The mistake is that the `lnode` is first deleted and then an attribute of the `lnode` is used, which was already deleted
+
+     Nature: "error" and memory leak"
+
+     Error location (if applicable): The mistake happens in the `if` function when `n` is deleted and recursively recalled.
+
+  3. Mistake: The mistake is that we only delete `c`without deleting the pointer pointing to the `subcell`.
+
+     Nature: "memory leak"
+
+     Error location (if applicable): The mistake happens when `c` is deleted.
+
+  4. Mistake: The mistake is that we try to delete an integer from the stack memory.
+
+     Nature: "error (undefined behaviour)"
+
+     Error location (if applicable): The mistake happens when `w` is deleted
+
+  5. Mistake: The mistake is that `delete` tries to delete the address and not the value allocated tot he memory.
+
+     Nature: "error (undefined behaviour)"
+
+     Error location (if applicable): The mistake happens when `&v[0]` is deleted.
+
+  #+END_src