Home/ Questions/Q 8917221
In Process

The Archive Base Latest Questions

Editorial Team
  • 0
Asked: 2026-06-15T05:26:05+00:00

I’m running some code which may be pointing out I don’t understand the difference

  • 0

I’m running some code which may be pointing out I don’t understand the difference between the heap and stack that well. Below I have some example code, where I either declare an array on the stack or the heap of 1234567 elements. Both work.

int main(int argc, char** argv){

  int N = 1234567;

  int A[N];

  //int* A = new int[N];

}

But if we take N to be 12345678, I get a seg fault with int A[N], whereas the heap declaration still works fine. (I’m using g++ O3 -std=c++0x if that matters). What madness is this? Does the stack have a (rather small) array size limit?

Share

Leave an answer

You must login to add an answer.

Need An Account,

1 Answer

  1. Editorial Team

    The heap grows dynamically with allocation through malloc and co. The stack grows with each function call made in the course of running a program. The return address, arguments, local variables are usually stored in the stack (except that in certain processor architectures a handful of these are stored in registers instead). It is also possible (but not common) to allocate stack space dynamically.

    The heap and the stack compete for the use of the same memory. You can think on one growing left to right and the other growing right to left. There is a possibility that, if left unchecked, they may collide. The stack is typically restrained from growing beyond a certain bound. This is relatively small because it is expected that it will use only a few bytes for most calls and only a few stack levels will be used. The limit is small but sufficient for most tasks. You can expand this limit by changing your build settings (not for Linux ELF binaries though) or by calling setrlimit. The OS may also impose a limit which you can change. There may be soft and hard limits (http://www.nics.tennessee.edu/node/327).

    Going into greater detail about the limits falls outside the scope of the question. The bottomline is that the stack is limited and it is quite small because it competes with the heap for actual memory and for typical applications it need not be bigger.

    http://en.wikipedia.org/wiki/Call_stack

    • 0