what is wrong with this code please

okay i have the following structure in place:

Code:

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typedef struct connections connections;
struct connections{  // Structure to contain information about connections to items
    int ID;  // The identification number of the connected item
    float strength;  // A float to represent the strength of the  connection.
        connections * next;  // Pointer to the next connection in the list.
};


typedef struct theNode theNode;
struct theNode{  // The main structure that represents an item of Organism or Resource
        int id;  // The identification number of the item
        float levels[ARMAX];  // The array of floats. Limited to 5 indexes
        connections * conn;  // Pointer to a list of connections
};

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all this works fine i assume cause it gives me no errors in other parts of the code, the next section keeps crashing my system

Code:

---

struct theNode *temp = NULL;
        struct connections  *tmp = NULL;
        int len = 0;
        float strength; //Variable used to hold connection strength
       
        switch(message)
        {
        case WM_INITDIALOG:
                return TRUE;
        case WM_COMMAND:
                switch(LOWORD(wParam))
                {
                case IDOK:
                        len = GetWindowTextLength(GetDlgItem(hwnd, IDC_EDIT_STRENGTH));
                        if(len > 0)
                        {
                                char* buf1;
                                buf1 = (char*)GlobalAlloc(GPTR, len + 1); //allocate memory
                                GetDlgItemText(hwnd, IDC_EDIT_STRENGTH, buf1, len + 1);
                                //call to convertTextToNum function and populate traits array
                                strength = convertTextToNum(buf1);
                                GlobalFree((HANDLE)buf1); //free the memory


                                ConPrintf( hCon,255,"ID # = %d\n", index);//debug
                                ConPrintf( hCon,255,"Connection ID # = %d\n", index2);//debug
                                ConPrintf( hCon,255,"Connection Strength = %0.3f\n", strength);//debug
               

                                temp = theItems[index];

                                tmp = temp->conn;
                               
                                tmp->ID = index2; // <----crashes here in debug when i watch
                                tmp->strength = strength;

                                addConnection2(tmp, index); //add connections to organism/resource
                               
                        }
                       
                        EndDialog(hwnd, IDOK);
                        break;
                }
                break;
                default:
                        return FALSE;
        }
        return TRUE;

---

both index and index2 are static ints declared elsewere, i am new to visual studio and am confused by the CXX0030 code that appears when i debug

i hope i explained this and gave enough code

thanx in advance

korbitz

Code:

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        temp = theItems[index];

        tmp = temp->conn;
                               
        /* Add line to see value of tmp before we use it */
        ConPrintf( hCon,255,"tmp = %p\n", tmp);//debug

        tmp->ID = index2; // <----crashes here in debug when i watch

---

When you crash dereferencing a pointer it means that the pointer is either NULL or not valid. Therefore your problem is not here but when you set(or fail to set) the value of temp->conn.

thanx for the reply

okay checked value of tmp and its output is 00000000

Quote:

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Therefore your problem is not here but when you set(or fail to set) the value of temp->conn.

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hmmmm, bit unsure what you mean there, i assume i need to initialise the variables contained within the structure

or am i missing the point all together??

>>okay checked value of tmp and its output is 00000000<<
In the context of a pointer 0 is NULL.

>>hmmmm, bit unsure what you mean there, i assume i need to initialise the variables contained within the structure<<

Yes you should have done this earlier in your code or maybe you want to allocate temp->conn if it is NULL?

Code:

---

if (temp->conn == NULL)
{
        temp->conn = (connections *) malloc(sizeof(connections));
        if (temp->conn == NULL) exit(-1); // Out of memory
}

tmp = temp->conn;

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