c++arraysout-of-memorystack-overflowbitset

C++ Difference between global and non-global arrays (Stackoverflow Exception)

When I write the following program, it works correctly i.e. the bitset array is declared outside the main() method.

Correctly Works

#include <iostream>
#include <bitset>

using namespace std;

bitset<5000> set[5000];

int main(){
    cout<<"program runs fine"<<endl;
    return 0;
}

But I get stack-overflow exception when I create it inside the main method. Can anyone explain in detail as to what is going on here? Normally I see stack-overflow exceptions in recursive methods. So who is using the stack here?

#include <iostream>
#include <bitset>

using namespace std;


int main(){
    bitset<5000> set[5000];
    cout<<"program runs fine"<<endl;
    return 0;
}

Doesn't work and throws stack-overflow exception enter image description here

Solution

  • Declaring it in main is declaring it in "automatic storage" AKA the stack. Declaring it outside of main, is declaring it in "static storage" AKA global data. You are declaring a ton of data. std::bitset<5000> is 632 bytes on my system with VS2013 (likely an alignment from 5000/8). And you are declaring 5000 of them. 5000 * 632 = 3 160 000 bytes, or roughly 3 Megabytes. Default in VS2013 is 1 megabyte for the stack, which is why you are seeing an overflow.

    There are three kinds of storage: automatic, storage, and dynamic. These are colloquially referred to as stack, static (in some cases, global) and heap memory respectively:

    int static_int;

int main() {
  int automatic_int;
  static int local_static_int; // also static storage!
  int * dynamic_int_ptr = new int;
}