Question

Suppose your program contains code to create a dynamic array as in SelfTest Exercise \(10,\) and suppose the pointer variable entry has not had its (pointer) value changed. Write code to destroy this new dynamic array and return the memory it uses to the freestore.

Short answer

Answer: To deallocate a dynamic array and prevent dangling pointers, follow these steps: 1. Verify that the pointer variable still holds the same address. 2. Use the 'delete[]' operator to deallocate the memory occupied by the dynamic array. 3. Set the pointer variable to nullptr.

Step-by-step solution

Verify that the pointer variable 'entry' still holds the same address

Before deallocating the memory, ensure that the pointer variable 'entry' hasn't changed its address. ```cpp if (entry != nullptr) { // Proceed to next step } ```

Use the 'delete' operator to deallocate the memory

We can use the 'delete[]' operator to deallocate memory occupied by the dynamic array. ```cpp if (entry != nullptr) { delete[] entry; // Proceed to next step } ```

Set the pointer variable 'entry' to nullptr

After deallocating the memory, set the pointer variable 'entry' to nullptr to prevent dangling pointers. ```cpp if (entry != nullptr) { delete[] entry; entry = nullptr; } ``` With these three steps, we have successfully deallocated the memory occupied by the dynamic array and prevented any possible dangling pointers.

Key concepts

Dynamic Array

In C++, a dynamic array is a type of array whose size can be determined during runtime. This flexibility is achieved through the use of dynamic memory allocation using pointers. Dynamic arrays offer several advantages:

• They allow for the creation of arrays where the size isn't known until the program is running. This is crucial in scenarios where input data size isn't predetermined.
• Memory is allocated from the heap. Hence, we can request larger memory than what stack arrays might allow.
• Dynamic arrays can be resized, unlike fixed-size static arrays.

To create a dynamic array, you typically use the 'new' keyword in C++. For example: ```cpp int* array = new int[size]; ``` This line allocates memory for an integer array of the specified 'size' at runtime and assigns the starting address of this array to the pointer variable 'array'. While dynamic arrays are powerful, they require careful handling to avoid common pitfalls associated with manual memory management.

Pointer Variables

Pointer variables in C++ are used to store addresses of other variables. They play a critical role when dealing with dynamic memory. Understanding pointers is crucial, especially when working with dynamic arrays or any dynamic data structures.

• A pointer is declared by specifying the data type it points to, followed by an asterisk (*) and the name of the pointer.
• It allows direct access to the memory location which is efficient for many operations.
• Pointers enable dynamic memory allocation, which is vital for creating data structures at runtime.

For example, when you write: ```cpp int* ptr; ``` This declares a pointer 'ptr' that can store the address of an integer variable. The pointer can then reference other variables or point to dynamically allocated memory. Correct use of pointers ensures efficient and safe management of resources. However, misuse can lead to errors such as memory leaks and undefined behavior.

Memory Deallocation

Memory deallocation is a process of releasing the memory allocated during runtime back to the system. In C++, this is explicitly done by using the 'delete' or 'delete[]' operators. Proper memory deallocation prevents memory leaks, which can degrade system performance over time.

• For single object allocations, use 'delete'.
• For arrays, use 'delete[]' to free up memory.
• Always check if the pointer is not null before deallocating.

For a dynamically allocated array, you would write: ```cpp delete[] array; ``` This code snippet releases the memory that the dynamic array occupies. Regular and diligent memory deallocation is a good practice in C++, ensuring the efficient use of resources. Failing to deallocate memory results in "memory leaks," where allocated memory is unusable but still occupies space.

Dangling Pointers

A dangling pointer arises when an object is deleted or deallocated without redirecting the pointer holding its address. This results in a pointer pointing to a memory location that is no longer valid. Dangling pointers can lead to undefined behavior if accessed mistakenly.
To prevent dangling pointers, follow these best practices:

• After deallocating memory, immediately set the pointer to nullptr.
• Avoid returning pointers to local variables outside the function's scope.
• Be cautious with pointer arithmetic and indexing.

For example, after deallocating a dynamic array: ```cpp if (array != nullptr) { delete[] array; array = nullptr; } ``` This code snippet ensures that the 'array' pointer no longer references invalid memory, mitigating the risks associated with dangling pointers. By adopting these practices, you can write safer and more robust C++ programs.