linked list problems (null values)

I'm trying to load a bunch of information in to a linked list so I don't have to create a ton of class declarations. I want the pointer 'next', that points to the next link, to be null on the last link. I can't seem to accomplish this. I tried it a couple different ways and it either thinks the head link is null, or the link is never ending. If I treat the linked list as a list with only one link (just a head) then all goes well. So any help here would be appreciated.

Code:

//The beginning portion of my loading function where I think it's having trouble

bool LOADOBJ::LoadObjFromFile(char* filename)
{
    std::ifstream file; //create filestream
    file.open(filename); //open the file for reading
    if(!file.is_open()) return false; //if the file could not be opened
    else{

        /*first find next available spot in the list*/
        ObjectList *temp = GetNextSpace(); //get the next space available
        temp = new ObjectList; //allocate the space
        temp->face_count = 0; //set face count
        temp->vert_per_face.clear(); //set vertices per face
        temp->next = NULL; //set next link to NULL

//....... there's more to this function but its kind of long



//the function that finds the end of the link
//I tried dynamically allocating here vs. doing it inside the load
//function, but it doesn't make a difference

ObjectList* LOADOBJ::GetNextSpace()
{
    if(head == NULL){
        return head;
    }
    else if(head != NULL){
        ObjectList *temp = head;
        while(temp != NULL)
            temp = temp->next;
        return temp;
    }
}

//and the structure for the linked list

struct ObjectList
{
    ObjectList *next; //pointer to next loaded object
    vector<float> v_x, v_y, v_z; //store x, y, and z components for vertices
    vector<float> vn_x, vn_y, vn_z; //store x, y, and z components for vertice normals
    vector<float> vt_x, vt_y, vt_z; //store x, y, and z components for vertice textures
    vector<int> fv, fvt, fvn; //vertices, vertice textures, vertice normals of each face
    int face_count; //face count
    vector<int> vert_per_face; //vertices per face
    int fvarray[][4]; //face vertex array (not currently used)
};

//finally the class

class LOADOBJ
{
    private:
        ObjectList *head; //head ptr in linked list of loaded object files
        int obj_load_count; //number of loaded object files
        void Destroy(); //destroys first link in the list
        ObjectList* GetNextSpace(); //get next available space in the linked list
    public:
        LOADOBJ(); //constructor
        ~LOADOBJ(); //destructor
        
        bool LoadObjFromFile(char*); //load object file
        int GetFileCount(); //get number of object files that have been loaded
        bool isEmpty(); //determines if the linked list is empty
        bool RenderAllObjects(); //render all the objects loaded in the linked list
        
}; //end LOADOBJ class

> ObjectList *temp = GetNextSpace(); //get the next space available
Try
ObjectList *tail = GetNextSpace(); //get the next space available

Then after the rest of your blue code

Code:

if ( head == NULL ) {
  head = temp;
}
else {
  tail->next = temp;
}

You're already using <vector>, so read up on <list> as well.

I tried what you suggested and it worked for loading more than one object, but they some how did not end up being in the same linked list. It was more like I loaded obj1 to the head of the list, then loaded obj2 in to random space that was not access-able. I modified my constructor and GetNextSpace() function to get the link list set up properly. The problem I have now is I cannot load more than 2 objects in to the linked list. The program crashes on the third object load. So I am kind of stuck on why it will not go past two links. Here is what I have now...

Code:

bool LOADOBJ::LoadObjFromFile(char* filename)
{
    std::ifstream file; //create filestream
    file.open(filename); //open the file for reading
    if(!file.is_open()) return false; //if the file could not be opened
    else{
        
        /*first find next available spot in the list*/
        ObjectList *temp = GetNextSpace(); //the variable 'temp' is needed since the rest of my load function uses temp

//.... the rest of LoadObjFromFile....


//function for getting the next space
ObjectList* LOADOBJ::GetNextSpace()
{
    ObjectList *temp = head;
    if(temp == NULL){
        temp = new ObjectList;
        temp->face_count = 0;
        temp->next = NULL;
        head = temp;
        return head;
    }
    else if(temp != NULL){
        while(temp->next != NULL) temp = temp->next;
        
        ObjectList *tail = new ObjectList;
        tail->next = NULL;
        tail->face_count = 0;
        temp->next = tail;
        return tail;
    }
    //return temp;
}

//constructor
LOADOBJ::LOADOBJ()
{
    obj_load_count = 0; //nothing is loaded so zero
    head = NULL;// new ObjectList; //pointer points allocated space
}