Question

What are the different stages of memory in a heap?

Answer 1

The heap is a region of your computer's memory that is not managed automatically for you, and is not as tightly managed by the CPU. It is a more free-floating region of memory (and is larger). To allocate memory on the heap, you must use malloc() or calloc(), which are built-in C functions. Once you have allocated memory on the heap, you are responsible for using free() to deallocate that memory once you don't need it any more. If you fail to do this, your program will have what is known as a memory leak. That is, memory on the heap will still be set aside (and won't be available to other processes). As we will see in the debugging section, there is a tool called valgrind that can help you detect memory leaks.

Unlike the stack, the heap does not have size restrictions on variable size (apart from the obvious physical limitations of your computer). Heap memory is slightly slower to be read from and written to, because one has to use pointers to access memory on the heap. We will talk about pointers shortly.

Unlike the stack, variables created on the heap are accessible by any function, anywhere in your program. Heap variables are essentially global in scope.

When should you use the heap, and when should you use the stack? If you need to allocate a large block of memory (e.g. a large array, or a big struct), and you need to keep that variable around a long time (like a global), then you should allocate it on the heap. If you are dealing with relatively small variables that only need to persist as long as the function using them is alive, then you should use the stack, it's easier and faster. If you need variables like arrays and structs that can change size dynamically (e.g. arrays that can grow or shrink as needed) then you will likely need to allocate them on the heap, and use dynamic memory allocation functions like malloc(), calloc(), realloc() and free() to manage that memory "by hand". We will talk about dynamically allocated data structures after we talk about pointers.

ge memory (you're in charge of allocating and freeing variables)

• variables can be resized using realloc()