A range of memory that the operating system allocates as needed for a program. Multiple ranges can be allocated with multiple requests.
The malloc and free functions in C deal with the heap.
Properties, Pros and Cons
| Properties | Implications |
|---|---|
| Size is dynamic | ✅ You can store a large amount of memory without worrying about stack overflows ✅ You can store data structures of dynamic sizes 🚫 System Call for additional memory is slow |
| Inherently fragmented | ✅ Allows for data structure of dynamic sizes 🚫 Requires keeping track of a vtable, which takes up a bit of cycles and memory. 🚫 Allocations within the heap requires searching through sub-regions in the heap |
| Memory has to be manually managed | 🚫 Leading to runtime errors common to many low-level languages |
| Fast accessing times if used correctly |
Note
Using a heap isn’t inherently slow. It depends on the data structure used, and the allocation strategy.
Also, an allocation may not necessarily trigger a syscall. It may not if there ranges in the heap that can fit your data structure needs.