Access violation reading location 0xCDCDCDCD

Question

As the title states, I'm getting an error

Access violation reading location 0xCDCDCDCD.

Now I'm dealing with an array of linked lists, and I believe the trouble to be something around adding to the linked list. I'm fine with this usually, but I feel I'm doing something wrong with memory allocation.

Here are my structs:

Graph:

typedef struct graph
{
    int V;
    int *state;
    EdgeList *edges;
} Graph;

Edge:

typedef struct edge
{
    int toVertex;
    int weight;
} Edge;

EdgeList:

typedef struct edgeNode
{
    Edge edge;
    struct edgeNode *next;
} *EdgeList;

Here is the main function that runs it all:

main()
{
    Graph myGraph;
    scanf("%d", &(myGraph.V));
    myGraph.state = (int)malloc(myGraph.V*sizeof(int));
    myGraph.edges = (EdgeList*)malloc(myGraph.V*sizeof(EdgeList));
    int *inDegrees;
    inDegrees = (int)malloc(sizeof(int)*myGraph.V);

    /*  Sets all array values to 0  */
    for (int counter = 0; counter < myGraph.V; counter++)
    {
        inDegrees[counter] = 0;
    }


    for (int i = 0; i < myGraph.V; i++)
    {
        int number_of_edges;
        int input = 0;  /*For that little experimental bit*/
        scanf("%d", &(myGraph.state[i]));
        scanf("%d", &number_of_edges);
        if (number_of_edges > 0)
        {
            for (int j = 0; j < number_of_edges; j++)
            {
                Edge newEdge;
                scanf("%d,%d", &(newEdge.toVertex), &(newEdge.weight));
                inDegrees[newEdge.toVertex]++;
                printf("%s%d\n", "\nOoh, new input for ", newEdge.toVertex);

                /*insert at front*/
                EdgeList newNode = (EdgeList)malloc(sizeof (struct edgeNode));
                newNode->edge = newEdge;

                newNode->next = myGraph.edges[i];
                myGraph.edges[i] = newNode;


                /* Bit to calculate state.*/

                EdgeList current = myGraph.edges[i];

                while (current != NULL)
                {
                    if (current->edge.toVertex == i)
                    {
                        input += (current->edge.weight)*(myGraph.state[i]);
                    }
                    current = current->next;
                }
            }
            if (input > 0)
            {
                myGraph.state[i] = 1;
            }
            else
            {
                myGraph.state[i] = 0;
            }
        }
    }

    //print
    for (int k = 0; k < myGraph.V; k++)
    {
        printf("\n%s%d%s", "In degrees for ", k, ": ");
        printf("%d", inDegrees[k]);
    }

}

In particular, the error comes during the traversal of the linked list. It's in the above code, but I'll highlight it here:

EdgeList current = myGraph.edges[i];

while (current != NULL)
{
    if (current->edge.toVertex == i)
    {
        input += (current->edge.weight)*(myGraph.state[i]);
    }
    current = current->next;
}

If anyone can help, it'd be greatly appreciated because I'm rather stuck.

Answer 1

1. An value in uninitialized buffer allocated via malloc() is assigned to newNode->edge in newNode->next = myGraph.edges[i];.
2. The newNode is set to current via myGraph.edges[i] = newNode; and EdgeList current = myGraph.edges[i];.
3. Assuming that malloc() succeeded, current isn't NULL here, so it is entering the loop.
4. The uninitialized value assinged in 1 is assigned to current in current = current->next;.
5. An undefined behavior is invoked by using value in buffer allocated via malloc() and uninitialized at current != NULL.

To fix this error, initialize myGraph.edges in, for example, this way:

myGraph.edges = (EdgeList*)malloc(myGraph.V*sizeof(EdgeList));
for (int i = 0; i < myGraph.V; i++)
{
    myGraph.edges[i] = NULL;
}

Also, remove the harmful casts to int of the pointer returned from malloc(). Casting the return values to pointers explicitly is also not considered as good.