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When is it best to use a Stack instead of a Heap and vice versa?
I've read a few of the other questions regarding the heap vs stack, but they seem to focus more on what the heap/stack do rather than why you would use them.
It seems to me that stack allocation would almost always be preferred since it is quicker (just moving the stack pointer vs looking for free space in the heap), and you don't have to manually free allocated memory when you're done using it. The only reason I can see for using heap allocation is if you wanted to create an object in a function and then use it outside that functions scope, since stack allocated memory is automatically unallocated after returning from the function.
Are there other reasons for using heap allocation instead of stack allocation that I am not aware of?
The advantages of heap memory are: Lifetime. Because the programmer now controls exactly when memory is allocated, it is possible to build a data structure in memory, and return that data structure to the caller. This was never possible with local memory, which was automatically deallocated when the function exited.
Stack accesses local variables only while Heap allows you to access variables globally. Stack variables can't be resized whereas Heap variables can be resized. Stack memory is allocated in a contiguous block whereas Heap memory is allocated in any random order.
Stack memory allocation is considered safer as compared to heap memory allocation because the data stored can only be access by owner thread. Memory allocation and de-allocation is faster as compared to Heap-memory allocation. Stack-memory has less storage space as compared to Heap-memory.
Basically, the heap is more flexible than the stack. That's because memory space for the heap can be dynamically allocated and de-allocated as needed. However, memory of the heap can at times be slower when compared to that stack.
There are a few reasons:
malloc
/calloc
to free
);Without the flexible object lifetime, useful data structures such as binary trees and linked lists would be virtually impossible to write.
The big one is #1. As soon as you get into any sort of concurrency or IPC #1 is everywhere. Even most non-trivial single threaded applications are tricky to devise without some heap allocation. That'd practically be faking a functional language in C/C++.
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