Question

Suppose a dynamic variable were created as follows: char \(* p\); \(p=\) new char; Assuming that the value of the pointer variable \(p\) has not changed (so it still points to the same dynamic variable), how can you destroy this new dynamic variable and return the memory it uses to the freestore so that the memory can be reused to create new dynamic variables?

Short answer

Answer: To free the memory allocated to a dynamic character variable without changing the pointer value, use the `delete` operator to return the memory to the freestore. This will still allow the pointer to point to the memory location, but you should not use the pointer without allocating new memory as it may lead to undefined behavior. For example: ```cpp char *p; p = new char; delete p; ```

Step-by-step solution

Allocate memory for the dynamic variable

We are given a character pointer `p` and a new dynamic variable being allocated as: ```cpp char *p; p = new char; ``` Here, memory has been allocated dynamically for a character variable.

Use the 'delete' operator to free memory

To return the memory used by the dynamic variable to the freestore, use the `delete` operator: ```cpp delete p; ``` This statement will free the memory allocated to the character pointed at by `p` and return it to the freestore. The pointer `p` will not change its value and will still point to the memory location that has now been freed. However, do not use `p` without allocating new memory to it because it still points to the freed memory and accessing it would lead to undefined behavior. Now, the memory is available in the freestore and can be reused to create new dynamic variables.

Key concepts

Delete Operator

When working with dynamic memory allocation in C++, the delete operator plays a crucial role as it is responsible for releasing previously allocated memory back to the system—referred to as the freestore or heap. Imagine you've reserved a room for a meeting; once the meeting is over, you should inform the reception that the room is now free for others to use. Similarly, after using dynamically allocated memory in your program, you directly inform the system that it's available for reuse by using delete p;.

Without Deleting the memory, you would create a memory leak, meaning that memory would remain reserved and unaccessible to other parts of your program, which could lead to shortage of memory for new allocations and eventually might cause the program or system to become unstable.

Dynamic Variable

Dynamic variables in C++ are so-named because their lifetime is dynamically managed during the runtime of the program. They are not predefined in the source code and can be created or destroyed on the fly. Think of them as guests in a hotel; they can check-in and check-out anytime, unlike the building's staff (like static variables) who are always there. Dynamic variables are created using the new operator, and their lifetime is controlled manually by the programmer.

Using char *p = new char; acquires a block of memory large enough to store a char and p holds the address of this memory block. When you no longer need the variable, you must remember to release the memory with delete p; to avoid memory leaks. Proper management of dynamic variables ensures efficient memory usage.

Freestore Management

Freestore management can be thought of as organizing the use of a shared resource—memory—in an optimal manner. The freestore, also known as the heap, is a pool of memory that programs use for dynamic allocation during runtime. When you use new to allocate a dynamic variable, C++ takes care of finding a free spot in the freestore to give you. After you're done using that space for your variable, it's good practice (and courteous to your future self and other programs) to clean up by using delete to return the space to the freestore.

Without proper freestore management, just like a poorly managed parking lot, your program could run out of space, resulting in memory allocation errors that can halt your application. It's essential to maintain an orderly freestore by freeing memory promptly when not in use.

Pointer Variables

In C++, pointer variables are akin to treasure maps; they store the address of a memory location rather than the treasure (data) itself. They allow you to indirectly access and manipulate data stored in memory. When you create a pointer variable, such as char *p;, you are holding the address of a character variable.

Pointer variables become even more powerful when paired with dynamic memory allocation. They are the bridge between your code and the memory addresses allocated by the new operator. But remember, the map is not the treasure; after allocating memory with new, always ensure that the pointer directing to this memory is managed correctly—use the pointer to access or modify the data and, when done, use delete to clean up, preventing 'dangling pointers' that lead nowhere.