Thread: Segmentation Fault

  1. #1
    Registered User
    Join Date
    Dec 2010

    Question Segmentation Fault

    Hey all,

    I had previous question that was expertly answered today, and now I have another issue. I am trying to display the values I entered into a dynamic 2-dimensional array, but when my code gets to the display loop, I get a segmentation fault. My code so far is below.

    main()  {
            int i, j;
            double *CellPtr;
            //values to hold row & col size for array & mem size needed
            int col, row, Doubles;
            printf("\nEnter the number of columns desired for your array \n");
            scanf("%d", &col);
            printf("\nEnter the number of rows desired for your array \n");
            scanf("%d", &row);
            Doubles = col * row;
            //declaring the array
            double **ArrayPtr;
            ArrayPtr = malloc(row * sizeof(double *));
            for(i = 0; i < row; i++)
                    ArrayPtr[i] = malloc(col * sizeof(double));
            //filling the array with the requested values
            for(i = 0; i < row; i++)
                    for(j = 0; j < col; j++)        {
                            *ArrayPtr = (int) i * 100 + j;
            for(i = 0; i < row; i++)
                    for(j = 0; j < col; j++)
                            printf("%d\n", ArrayPtr[i][j]);
    I hope it's OK to include the whole program; it's pretty small.

    If anyone could let me know why I'm getting the segmentation fault (or if there's a glaring, horrific error in my display code logic), I'd really appreciate it.

    Thanks in advance!

  2. #2
    and the Hat of Guessing tabstop's Avatar
    Join Date
    Nov 2007
    You moved your ArrayPtr hither and yon throughout the thickets of your doubly-subscripted array. Now: how are you going to get it back?

    (EDIT: And for bonus fun: who says your doubly-subscripted array is all stored in order?)

  3. #3
    and the hat of int overfl Salem's Avatar
    Join Date
    Aug 2001
    The edge of the known universe
    > printf("%d\n", ArrayPtr[i][j]
    You should have used this notation to write to the array.

    You also need to look up how to use printf as well - %d is not for doubles.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.

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