queue.h

#ifndef QUEUE_H
#define QUEUE_H
#include <cstdlib>
#include <cstring>

// Array-based waiting queue
// Initialised with a max size and resizable when necessary
// Example use:
// Queue<int> q(10);
// q.Enqueue(1);
// q.Pop();
template <typename E>
class Queue
{
public:
	Queue(size_t s)
	{
		front_ = 0;
		rear_ = 0;
		max_size_ = s;
		len_ = 0;
		buffer_ = (E*)malloc(s*sizeof(E));
	};

	~Queue()
	{
		free(buffer_);
		buffer_ = NULL;

	};

	bool is_empty() const { return !len_; }

	size_t get_length() const { return len_; }

	const E& get_front() const { return buffer_[front_]; }

	void clear() { rear_ = front_ = len_ = 0; }

	void Enqueue(const E& element)
	{
		if (rear_ == max_size_){
			if (len_ < max_size_) {
				// reached rear limit but queue not full
				// shift content to the front
				memmove((void*)buffer_,(void*)(buffer_+front_),len_*(sizeof(E)));
				front_ = 0;
				rear_ = len_;
			} else {
				// queue at max capacity, allocate double space
				buffer_ = (E*)realloc(buffer_,(max_size_ <<= 1)*sizeof(E));
			}
		}
		buffer_[rear_++]=element;
		++len_;
	}

	void Pop()
	{
		if (len_) {
			++front_;
			--len_;
		};
	}

private:
	E *buffer_;
	size_t front_;  // index to pop from
	size_t rear_;   // index to enqueue
	size_t len_;
	size_t max_size_;
};

#endif