Circular linked list: How to correct my remove node function?

I am learning circular linked list. I face a problem when calling deleteNodeByKey() to remove head node. It works for the rest of the nodes for remove. Why is it not working if remove node is head?

#include <iostream>
#include <stdlib.h>
using namespace std;

/* structure for a node */
struct node
{
    int data;
    struct node *next;
};

/* Function to insert a node at the begining of a Circular
   linked list */
void push(struct node **head_ref, int data)
{
    struct node *ptr = (struct node*)malloc(sizeof(struct node));
    ptr->data = data;
    ptr->next = *head_ref;
    struct node *temp = *head_ref;
     /* If linked list is not NULL then set the next of last node. 
        It is going to last node by circling 1 times.
     */
    if(*head_ref != NULL){
        while(temp->next != *head_ref){
            temp = temp->next;
        }
        //set last node by ptr
        temp->next = ptr;
    }
    else{
        // 1 node circular linked list
        ptr->next = ptr;
    }
    // after push ptr is the new node
    *head_ref = ptr;
}

//get the previous node
struct node* getPreviousNode(struct node* current_node){
    struct node* prev = current_node;
    while(prev->next != NULL && prev->next->data != current_node->data ){
        prev = prev->next;
    }
    return prev; 
}


/* Given a reference (pointer to pointer) to the head of a list
   and a key, deletes the first occurrence of key in linked list */
void deleteNodeByKey(struct node **head_ref, int key)
{
    // Store head node
    struct node* current_node = *head_ref, *prev;


    while(current_node != NULL && current_node->data != key){
        current_node = current_node->next;   
    }

    if(current_node == NULL){
        return;
    }

    //Removing the node
    if(current_node->data == key){
        prev = getPreviousNode(current_node);
        prev->next = current_node->next; 
        current_node->next = NULL;
        free(current_node);               
        return;
    }
}


/* Function to print nodes in a given Circular linked list */
void printList(struct node *head)
{
    struct node *temp = head;
    if(head != NULL){
        /*
            do-while because at 1st temp points head 
            and after 1 rotation temp wil come back to head again
        */
        do{
            cout<<temp->data<<' ';
            temp = temp->next;
        }
        while(temp != head);
        cout<<endl;
    }
}

int main() {
     /* Initialize lists as empty */
    struct node *head = NULL;
    /* Created linked list will be 11->2->56->12 */
    push(&head, 12);
    push(&head, 56);
    push(&head, 2);
    push(&head, 11);
    cout<<"Contents of Circular Linked List"<<endl;
    printList(head);

    deleteNodeByKey(&head, 11);
    printList(head);

    return 0;
}

Here is the code link: Source Code

Solution

inside deleteNodeByKey() function i add an if() block to re assign head node to it's next node:

 //Removing the node
    if(current_node->data == key){
        //following if() is newly added
        //key is inside head node
        if(current_node == *head_ref ){
            //changing the head point to next
            *head_ref = current_node->next;
        }
        prev = getPreviousNode(current_node);
        prev->next = current_node->next; 
        current_node->next = NULL;
        free(current_node);               
        return;
    }