Problem Modifying Struct Member Passed Into Function

Struct:

Code:

typedef struct tnode { 
        int id; 
        char *artist;
        char *title; 
        char *remixer;
        char *label; 
        int year;
        char *genre; 
        char *project;
        int mark;
        char *class; 
        int class_number;
        struct tnode *next;
        struct tnode *prev;
} Treenode;

I made a head pointer in main, and I set the current pointer to the head:

Code:

/* Set tree_current_ptr to the tree head. */
tree_current_ptr = tree_head_ptr;

I call this function with the tree_current_ptr so that its position can get modified in the function:

Code:

void print_rows(Treenode **start, Windownode *node, float *spaces, int num_rows, int direction)
{
        int count_rows;
        int pos_y, pos_x=0;
        int limit;

        Treenode *cur = *start; 

#ifdef _DEBUG_ 
        curs_set(1);
#endif

        if(direction == PRINT_FWD) {
                pos_y = 0;
                limit = node->sub_window->display->max_y;

                for(count_rows=0; cur && (count_rows < num_rows) && (pos_y < limit); ++count_rows, ++pos_y, cur=cur->next) {
                        print_row(node->sub_window, cur, spaces, pos_y, pos_x); 
                        wrefresh(node->sub_window->win);
                }

        } else if (direction == PRINT_BKWD) {
                pos_y = node->sub_window->display->max_y - 1;
                limit = 0;

                for(count_rows=0; cur && (count_rows < num_rows) && (pos_y >= limit); ++count_rows, --pos_y, cur=cur->prev) {
                        print_row(node->sub_window, cur, spaces, pos_y, pos_x); 
                        wrefresh(node->sub_window->win);
                }
        }

#ifdef _DEBUG_ 
        curs_set(0);
#endif

}

In main I do:

Code:

print_rows(&tree_current_ptr, win_parent[MAIN], spaces, 40, PRINT_FWD);

However, in the for loop, when I set cur = cur->next, the tree_current_ptr comes out unaltered. My code like this compiles. I tried setting it like (*cur)=cur->next, but that didn't compile. I also tried just passing a pointer to the struct as a parameter, but that didn't work. What am I missing about modifying the struct member?

I'm simply returning the current pointer from the function. Thanks anyways!