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A weird segmentation fault error with 2D array

This is a discussion on A weird segmentation fault error with 2D array within the C Programming forums, part of the General Programming Boards category; Hi there, I'm experiencing a weird segmentation fault. The following code runs fine Code: #include <stdlib.h> #include <stdio.h> main() { ...

  1. #1
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    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.

  2. #2
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    Quote Originally Posted by uwowizard View Post
    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.
    Salem likes this.

  3. #3
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    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.

  4. #4
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    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

  5. #5
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    Quote Originally Posted by uwowizard View Post
    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

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