Heap memory

Heap Memory

• The heap is an area of dynamically-allocated memory that is managed automatically by the operating system or the memory manager library. Memory on the heap is allocated, deallocated, and resized regularly during program execution, and this can lead to a problem called fragmentation.
• Fragmentation occurs when memory objects are allocated with small spaces in between that are too small to hold additional memory objects. The net result is a percentage of the heap space that is not usable for further memory allocations.
• Heaps are also susceptible to overflow situations, although the results are typically not as dire as in a stack overflow. It's not impossible for a hacker to disrupt the system through a heap overflow, but it's particularly difficult.
• Note that the name heap has nothing to do with heap data structure. It is called heap because it is a pile of memory space available to programmers to allocated and de-allocate. If a programmer does not handle this memory well, memory leak can happen in the program.

int main() 
{ 
   // This memory for 30 integers 
   // is allocated on heap. 
   int *ptr  = new int[30]; 
} 

• Differences Between Stack and Heap Allocations

1. In a stack, the allocation and deallocation is automatically done by whereas, in heap, it needs to be done by the programmer manually.
2. Handling of Heap frame is costlier than handling of stack frame.
3. Memory shortage problem is more likely to happen in stack whereas the main issue in heap memory is fragmentation.
4. Stack frame access is easier than the heap frame as the stack have small region of memory and is cache friendly, but in case of heap frames which are dispersed throughout the memory so it cause more cache misses.
5. Stack is not flexible, the memory size allotted cannot be changed whereas a heap is flexible, and the allotted memory can be altered.
6. Accessing time of heap takes is more than a stack.