Stack Memory vs Heap Memory

Question

Possible Duplicate    What and where are the stack and heap       I am programming in C   and I am always wondering what exactly is stack memory vs heap memory  All I know is when I call new  I would get memory from heap  If if create local variables  I would get memory from stack  After some research on internet  the most common answer is stack memory is temporary and heap memory is permanent    Is stack and heap memory model a concept of operating system or computer architecture  So some of it might not follow stack and heap memory model or all of them follow it   Stack and heap memory is the abstraction over the memory model of the virtual memory   which might swap memory between disk and RAM   So both stack and heap memory physically might be RAM or the disk  Then what is the reason where heap allocation seems to be slower than the stack counterpart    Also  the main program would be run in the stack or a heap   Also  what would happen if a process run out of the stack memory or heap memory allocated   Thanks

User · Answer

It s a language abstraction - some languages have both  some one  some neither   In the case of C    the code is not run in either the stack or the heap  You can test what happens if you run out of heap memory by repeatingly calling new to  allocate memory in a loop without calling delete to free it it  But make  a system backup before doing this

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Stack memory is specifically the range of memory that is accessible via the Stack register of the CPU  The Stack was used as a way to implement the  Jump-Subroutine - Return  code pattern in assembly language  and also as a means to implement hardware-level interrupt handling  For instance  during an interrupt  the Stack was used to store various CPU registers  including Status  which indicates the results of an operation  and Program Counter  where was the CPU in the program when the interrupt occurred    Stack memory is very much the consequence of usual CPU design  The speed of its allocation deallocation is fast because it is strictly a last-in first-out design  It is a simple matter of a move operation and a decrement increment operation on the Stack register   Heap memory was simply the memory that was left over after the program was loaded and the Stack memory was allocated  It may  or may not  include global variable space  it s a matter of convention    Modern pre-emptive multitasking OS s with virtual memory and memory-mapped devices make the actual situation more complicated  but that s Stack vs Heap in a nutshell

User · Answer

In C   the stack memory is where local variables get stored constructed  The stack is also used to hold parameters passed to functions    The stack is very much like the std  stack class  you push parameters onto it and then call a function  The function then knows that the parameters it expects can be found on the end of the stack  Likewise  the function can push locals onto the stack and pop them off it before returning from the function   caveat - compiler optimizations and calling conventions all mean things aren t this simple   The stack is really best understood from a low level and I d recommend Art of Assembly - Passing Parameters on the Stack  Rarely  if ever  would you consider any sort of manual stack manipulation from C     Generally speaking  the stack is preferred as it is usually in the CPU cache  so operations involving objects stored on it tend to be faster  However the stack is a limited resource  and shouldn t be used for anything large  Running out of stack memory is called a Stack buffer overflow  It s a serious thing to encounter  but you really shouldn t come across one unless you have a crazy recursive function or something similar   Heap memory is much as rskar says  In general  C   objects allocated with new  or blocks of memory allocated with the likes of malloc end up on the heap  Heap memory almost always must be manually freed  though you should really use a smart pointer class or similar to avoid needing to remember to do so  Running out of heap memory can  will   result in a std  bad alloc

[c++] Stack Memory vs Heap Memory

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