Thread: A weird segmentation fault error with 2D array

Hi there,

I'm experiencing a weird segmentation fault. The following code runs fine

Code:

#include <stdlib.h>
#include <stdio.h>


main()
{
    int matrixSize = 1000;
    int i,j;
    
    double a[matrixSize][matrixSize];
    for (i = 0; i < matrixSize; i++)
        for (j = 0; j < matrixSize; j++)
            a[i][j] = rand() % 10;
	    
    return 0;
}

But when I try to initialize one more 2D array, I get "segmentation fault" exception:

Code:

#include <stdlib.h>#include <stdio.h>


main()
{
    int matrixSize = 1000;
    int i,j;
    
    double a[matrixSize][matrixSize];
    for (i = 0; i < matrixSize; i++)
        for (j = 0; j < matrixSize; j++)
            a[i][j] = rand() % 10;
	    
    double b[matrixSize][matrixSize];
    for (i = 0; i < matrixSize; i++)
        for (j = 0; j < matrixSize; j++)
            b[i][j] = rand() % 10;


    return 0;
}

Could anybody tell me what's the issue here? Any help would be greatly appreciated..

Thank you in advance.

Originally Posted by uwowizard

Code:

    double b[matrixSize][matrixSize];

Code:

    static double b[matrixSize][matrixSize];

Try adding static; to make the second one from the heap instead of stack. You are likely crashing the stack.



Tim S.

Both those arrays are being declared in the stack - which is a small segment of memory.

For larger arrays/more arrays, malloc or calloc is your goto function for array allocation. LOTS of memory there.

You are probably running out of stack space. You either need to use dynamic allocation (malloc/free) or create a static variable so the heap is used instead.

Jim

Originally Posted by uwowizard

Hi there,

I'm experiencing a weird segmentation fault. The following code runs fine
Could anybody tell me what's the issue here? Any help would be greatly appreciated..

Thank you in advance.

Program stack = ~1 - 2 mb on most systems

1000 x 1000 x sizeof(double) = 8 mb