If you’re a programmer or someone who has a keen interest in computers, you are bound to have come across stack and heap memory. Many people wrongly use these terms interchangeably. It is essential to know what memory allocation looks like and how stack and heap allocation differs.

You may be familiar with the concepts of the heap and stack as data structures. But you should remember that heap and stack memory allocation is a different concept. Knowing these fundamental principles can make all the difference when debugging a complex coding issue or facing a tough job interview. Read on as we get down to understanding stack and heap memory allocation.


Stack Memory Allocation

Stack memory allocation is a temporary allocation method that takes place in the function call stack. The compiler manages the memory to allocate for temporary variables created by a programmer’s function. Once it has completely executed the code inside a function, the compiler will automatically free this temporary memory.

A program can access variables on the stack very quickly because they’re stored directly in main memory. A function or method can also call another function/method. It is therefore essential that the compiler effectively manages the different variables for each function call.

stack memory allocation
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A program allocates stack memory when it calls a function for the first time. If a programmer declares a variable or array within the specific function, the compiler will reserve additional memory on the function call stack.

Related: Heaps vs. Stacks: What Sets Them Apart?

It’s important to remember that the compiler does the allocation and deallocation of the stack automatically. As a result, the programmer does not need to worry about it. However, it’s good programming practice to consume as little stack memory as possible. This means writing code intelligently, in a way that does not require any temporary method variables.

Programmers often make the error of using a pointer to access data in stack memory. But the function call stack gets deallocated once the function returns. Sometimes the pointer will return the correct data despite the stack having been completely deallocated. But most of the time, the invalid memory pointer will return a junk value. It is always recommended to avoid such unreliable use of pointers.


Heap Memory Allocation

Memory allocated in the heap is often referred to as dynamic memory allocation. In contrast with stack memory, it’s the programmer’s job to allocate and deallocate memory in the heap. You can think of heap memory as a chunk of memory available to the programmer.

The heap memory size depends on the size of virtual memory available to the program. Heap memory is slower to access when compared to data stored in the function call stack. Programmers can explicitly allocate and deallocate blocks in the heap. This allows them to save the return value of functions or variables without running into junk values and overwritten memory segments.

allocating heap memory C++

In some programming languages such as C++, programmers use the new keyword to allocate the required memory size and delete to deallocate. It is also considered good practice to reset the pointers to null to avoid undefined behavior.


See also: Is C++ Still Relevant in 2021?

Because the programmer explicitly manages heap memory, they are responsible for freeing it before terminating the program. Failure to properly manage explicitly declared memory can cause memory leaks and dangling pointers. This can cause your code to have unexpected undefined breakdowns.

A Good Programmer Knows Their Memory

Memory allocation is an essential part of how programs work. A good programmer must be efficient in utilizing system resources. Understanding the intricate details of stack and heap memory allocation will allow you to become a better programmer.

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