Question

I’m trying to create a two dimensional linked list to hold a sparse matrix and have written this code to insert a new node at the right place:

void insertNewNode(node **rowHead, node **columnHead, int value, int row, int column) { 
    //Get to the correct position in the column linked list
    if (*columnHead == NULL) {
        *columnHead = malloc(sizeof(node));
    } else {
        while((*columnHead)->nextColumn != NULL && (*columnHead)->nextColumn->row < row)
            *columnHead = (*columnHead)->nextColumn;
    }

    //Get to the correct position in the row linked list.
    if (*rowHead == NULL) {
        *rowHead = malloc(sizeof(node));
    } else {
        while((*rowHead)->nextRow != NULL && ((*rowHead)->nextRow->column < column))
            *rowHead = (*rowHead)->nextRow;
    }

    node *newNode = malloc(sizeof(node));
    newNode->column = column;
    newNode->row = row;
    newNode->value = value;

    (*columnHead)->nextColumn = newNode;
    (*rowHead)->nextRow = newNode;
}

For some reason the last line:

(*rowHead)->nextRow = newNode;

is causing an EXC_BAD_ACCESS error while the previous line is not, and I’m not entirely sure why. Can anyone see a reason why this would occur?

Answer 1

It could just be a problem somewhere else in your program with how your row data is allocated/maintained, and your column data happens to be OK. Have you inspected the value of rowHead? Maybe it is null or a garbage value… then you can trace back from there to figure out how that is happening.