circular buffer in C

typedef struct circular_buffer
{
    void *buffer; // data buffer

    void *buffer_end; // end of data buffer

    size_t capacity; // maximum number of items in the buffer

    size_t count; // number of items in the buffer

    size_t sz; // size of each item in the buffer

    void *head; // pointer to head

    void *tail; // pointer to tail

} circular_buffer;

void cb_init(circular_buffer *cb, size_t capacity, size_t sz)
{
    cb->buffer = malloc(capacity * sz);
    if(cb->buffer == NULL)
        // handle error

    cb->buffer_end = (char *)cb->buffer + capacity * sz;
    cb->capacity = capacity;
    cb->count = 0;
    cb->sz = sz;
    cb->head = cb->buffer;
    cb->tail = cb->buffer;
}

void cb_free(circular_buffer *cb)
{
    free(cb->buffer);
    // clear out other fields too, just to be safe

}

void cb_push_back(circular_buffer *cb, const void *item)
{
    if(cb->count == cb->capacity)
        // handle error

    memcpy(cb->head, item, cb->sz);
    cb->head = (char*)cb->head + cb->sz;
    if(cb->head == cb->buffer_end)
        cb->head = cb->buffer;
    cb->count++;
}

void cb_pop_front(circular_buffer *cb, void *item)
{
    if(cb->count == 0)
        // handle error

    memcpy(item, cb->tail, cb->sz);
    cb->tail = (char*)cb->tail + cb->sz;
    if(cb->tail == cb->buffer_end)
        cb->tail = cb->buffer;
    cb->count--;
}