Segmentation fault during the initialization of array

Question

I have seen segmentation fault sometimes during the initialization of an array with huge size.

For ex:

#include<iostream>
#include<limits>
using namespace std;

int main()
{
    string h;
    cin >> h;
    int size=h.size();
    cout << size << endl;
    int arr[size][size];
    cout << arr[0][0]<<endl;
    arr[0][0]=1;
    cout << arr[0][0]<<endl;

return 0;
}

When the user input is a small string lets say "sample" the program is working fine.

When the user input is a big string where the size is for ex. >1500.Segmentation is seen during the initialization of the array int arr[size][size];

What can be the issue?Is there any problem in initializating the array like the one above.

Community · Accepted Answer · 2017-05-23 12:27:22Z

1

I think you are out of memory with those initializations, causing a stack overflow. I recommend to allocate it on the heap or by using a std:vector. See here: Segmentation fault on large array sizes

edited May 23, 2017 at 12:27

CommunityBot

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answered Oct 29, 2014 at 13:16

Andrea

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Westbrook · Accepted Answer · 2014-10-29 13:31:05Z

0

I think an array's size must always be a compile-time constant in C++ i.e. the value of your 'size' variable must be known at compile time.

If you want dynamic storage, use std::vector

answered Oct 29, 2014 at 13:31

Westbrook

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Community · Accepted Answer · 2017-05-23 10:26:00Z

0

MSDN states that the default stack size on Windows is 1 MB - in case of 1500 elements in each dimension your array would take up 1500 * 1500 * 4 bytes = 9000000 bytes = 8.58 megabytes, not sure about Linux (this states it to be 8 MB) - I guess it depends on the compiler and distributive. So either:

1) If you know that there is a limit for the string length increase the stack size accordingly with the /STACK linker flag on Windows or like posted in this answer on Linux

2) Allocate the array on heap - if you don't want to mess around with memory allocations std::vector or std::unique_ptr can be used as a container

edited May 23, 2017 at 10:26

CommunityBot

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answered Oct 29, 2014 at 13:31

Rudolfs Bundulis

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