Printing the keys of B+ Tree

Question

I would like to print the keys of B+ Tree the way it actually looks in C .For example in the following form

                 | 12 |20| 30|

         5|9|11|     |12|17|_|    |20|27|26|   |30|-|-|

The above tree is of order(fanout) 4. Top node is tree node. Any algorithm or pseudocode would be highly appreciated.

EDIT

data structure i am implementing the tree.And the code for implementing the tree. When I try to print the tree, i get segmentation fault in the line Enqueue(tempNode->pointers[i]); of module printBplus(root)

            typedef struct bplus{
                 void ** pointers;         /*These are the array of pointers that                each tree node contains*/
                 int * keys;               /*These are the array of keys in each tree node*/
                 struct bplus * parent;    /*This the pointer to the parent tree node */
                 bool is_Leaf;             /*To check if the node is leaf*/
                 int num_Keys;             /*This keeps track the number of active keys in the node */
                 struct bplus * next ;      /*This is the pointer to next level  tree,used for queuing and dequeing node*/ 
               } *bplus, bplus_node;

Enqueuing and dequeuing:

         void Enqueue(bplus a){
              bplus bplusTemp; 
                 if (queue == NULL) {       //bplus queue=NULL is global variable
                 queue = a
                   queue->next = NULL;
                      }  
            else {
              bplusTemp = queue; 
                while(bplusTemp->next != NULL) {
                  bplusTemp = bplusTemp->next;
                   }
           bplusTemp->next = a;
           bplusNew->next = NULL;                     
                    }
                  }


              bplus Dequeue( void ) {
                 bplus bplusTemp = queue;
                 queue = queue->next;
                 bplusTemp->next = NULL;
                 return bplusTemp;
                   }

Printing module

---

        void   PrintBplus(bplus root){
            int i;
            bplus tempNode;
            queue = NULL;
            Enqueue(root); /*It enques the root*/
                  if(root === leaf)
                      print the keys associated with it
       while(queue != NULL){
            tempNode = Dequeue();
       for(i=0; i < tempNode->num_Keys; i++)    
           printf("%d,",root->keys[i]);
                  if(tempNode->is_Leaf == false){
                      for(i=0; i <= tempNode->num_Keys; i++)
                         Enqueue(tempNode->pointers[i]);
                       }
                }

Answer 1

Use a BFS algorithm.

Basically by traversing the nodes using a FIFO queue, you'll get the layers one after another and then you can print them in the order you want.

Answer 2

I'm assuming that by "the way it actually looks", you mean a pretty diagram like how they print b-trees in a textbook.

Printing trees the way they actually look is a pretty-non trival problem if you want to solve it at the most general level. Concerns include:

• keys have variable length and should be centered
• keys at the top must be spaced far apart so keys at the bottom aren't squashed together
• an optimal solution would react to sparsity in the tree and avoid big empty spaces
• printing across multiple lines and the atomicity of your ASCII characters mean you have to figure out everything at once rather than relying on a recursive call.

I spent a while working on it in my data structures class but never arrived at a completely satisfying solution.