Circular Buffer in C++

circular_buffer.cpp

//===================================================================
// File: circular_buffer.cpp
//
// Desc: A Circular Buffer implementation in C++.
//
// Copyright © 2019 Edwin Cloud. All rights reserved.
//
//===================================================================

//-------------------------------------------------------------------
// Includes
//-------------------------------------------------------------------
#include <memory>

//-------------------------------------------------------------------
// Circular_Buffer (Class)
//     We will implement the buffer with a templated class so
//     the buffer can be a buffer of specified type.
//-------------------------------------------------------------------
template <class T> class Circular_Buffer {
private:
  //---------------------------------------------------------------
  // Circular_Buffer - Private Member Variables
  //---------------------------------------------------------------

  std::unique_ptr<T[]> buffer; // using a smart pointer is safer (and we don't
                               // have to implement a destructor)
  size_t head = 0;             // size_t is an unsigned long
  size_t tail = 0;
  size_t max_size;
  T empty_item; // we will use this to clear data
public:
  //---------------------------------------------------------------
  // Circular_Buffer - Public Methods
  //---------------------------------------------------------------

  // Create a new Circular_Buffer.
  Circular_Buffer<T>(size_t max_size)
      : buffer(std::unique_ptr<T[]>(new T[max_size])), max_size(max_size){};

  // Add an item to this circular buffer.
  void enqueue(T item) {

    // if buffer is full, throw an error
    if (is_full())
      throw std::runtime_error("buffer is full");

    // insert item at back of buffer
    buffer[tail] = item;

    // increment tail
    tail = (tail + 1) % max_size;
  }

  // Remove an item from this circular buffer and return it.
  T dequeue() {

    // if buffer is empty, throw an error
    if (is_empty())
      throw std::runtime_error("buffer is empty");

    // get item at head
    T item = buffer[head];

    // set item at head to be empty
    T empty;
    buffer[head] = empty_item;

    // move head foward
    head = (head + 1) % max_size;

    // return item
    return item;
  }

  // Return the item at the front of this circular buffer.
  T front() { return buffer[head]; }

  // Return true if this circular buffer is empty, and false otherwise.
  bool is_empty() { return head == tail; }

  // Return true if this circular buffer is full, and false otherwise.
  bool is_full() { return tail == (head - 1) % max_size; }

  // Return the size of this circular buffer.
  size_t size() {
    if (tail >= head)
      return tail - head;
    return max_size - head - tail;
  }
};

//---------------------------------------------------------------
// Main Function
//---------------------------------------------------------------
int main() {

  Circular_Buffer<uint32_t> cb(10);

  printf("\n === CircularBuffer Test ===\n");
  printf("Size: %zu\n", cb.size());

  uint32_t x = 1;
  printf("Enqueue 1, val: %d\n", x);
  cb.enqueue(x);
  printf("Size: %zu\n", cb.size());
  x = 2;
  printf("Enqueue 1, val: %d\n", x);
  cb.enqueue(x);
  printf("Size: %zu\n", cb.size());
  printf("Enqueue 1, val: %d\n", x);
  cb.enqueue(x);
  printf("Size: %zu\n", cb.size());
  x = cb.dequeue();
  printf("Dequeue: %d\n", x);
  printf("Size: %zu\n", cb.size());
  x = cb.dequeue();
  printf("Dequeue: %d\n", x);
  printf("Size: %zu\n", cb.size());
  x = cb.dequeue();
  printf("Dequeue: %d\n", x);
  printf("Size: %zu\n", cb.size());
  x = cb.dequeue();
  printf("Dequeue: %d\n", x);
  printf("Size: %zu\n", cb.size());
  printf("Empty: %d\n", cb.is_empty());
}

@jeremy-rifkin Using the new operator calls the default constructor of the object to initialize the allocated memory. I'm not sure there's an easy way to make this class usable with non-default-constructible objects except possibly using something like type erasure or c-style allocation via malloc which doesn't call an object's constructor. https://godbolt.org/z/TExGz15jW

@kylesemelka-figure The typical well-formed solution to avoid default constructing the whole underlying array is to essentially make a char array and do placement-new into that memory (this is how std::vector is commonly implemented)