C++版的循环缓冲区类（实际测试可用！）

/*
 * CCycleBuffer.h
 *
 *  Created on: 2013-5-27
 *      Author: shiguang
 */

#ifndef __test__CCycleBuffer__
#define __test__CCycleBuffer__
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <assert.h>
class CCycleBuffer
{
public:
	bool isFull();
	bool isEmpty();
	void Empty();
	int GetLength();
	CCycleBuffer(int size);
	virtual ~CCycleBuffer();
	int Write(char* buf, int count);
	int Read(char* buf, int count);
private:
	bool m_bEmpty, m_bFull;
	char * m_pBuf;
	int m_nBufSize;
	int m_nReadPos;
	int m_nWritePos;

public:
	int GetReadPos()
	{
		return m_nReadPos;
	}
	int GetWritePos()
	{
		return m_nWritePos;
	}
};
#endif /* defined(__test__CCycleBuffer__) */

/*
 * CCycleBuffer.cpp
 *
 *  Created on: 2013-5-27
 *      Author: shiguang
 */

#include "CCycleBuffer.h"
// 定义
CCycleBuffer::CCycleBuffer(int size)
{
	m_nBufSize = size;
	m_nReadPos = 0;
	m_nWritePos = 0;
	m_pBuf = new char[m_nBufSize];
	m_bEmpty = true;
	m_bFull = false;
}

CCycleBuffer::~CCycleBuffer()
{
	delete[] m_pBuf;
}

/************************************************************************/
/* 向缓冲区写入数据，返回实际写入的字节数                               */
/************************************************************************/
int CCycleBuffer::Write(char* buf, int count)
{
	if (count <= 0)
		return 0;
	m_bEmpty = false;
	// 缓冲区已满，不能继续写入
	if (m_bFull)
	{
		return 0;
	}
	else if (m_nReadPos == m_nWritePos) // 缓冲区为空时
	{
		/*                          == 内存模型 ==
		 (empty)             m_nReadPos                (empty)
		 |----------------------------------|-----------------------------------------|
		 m_nWritePos        m_nBufSize
		 */
		int leftcount = m_nBufSize - m_nWritePos;
		if (leftcount > count)
		{
			memcpy(m_pBuf + m_nWritePos, buf, count);
			m_nWritePos += count;
			m_bFull = (m_nWritePos == m_nReadPos);
			return count;
		}
		else
		{
			memcpy(m_pBuf + m_nWritePos, buf, leftcount);
			m_nWritePos =
					(m_nReadPos > count - leftcount) ?
							count - leftcount : m_nReadPos; // 计算未写入数据大小
			memcpy(m_pBuf, buf + leftcount, m_nWritePos);
			m_bFull = (m_nWritePos == m_nReadPos);
			return leftcount + m_nWritePos;
		}
	}
	else if (m_nReadPos < m_nWritePos) // 有剩余空间可写入
	{
		/*                           == 内存模型 ==
		 (empty)                 (data)                     (empty)
		 |-------------------|----------------------------|---------------------------|
		 m_nReadPos                m_nWritePos       (leftcount)
		 */
		// 剩余缓冲区大小(从写入位置到缓冲区尾)
		int leftcount = m_nBufSize - m_nWritePos;
		if (leftcount > count)   // 有足够的剩余空间存放
		{
			memcpy(m_pBuf + m_nWritePos, buf, count);
			m_nWritePos += count;
			m_bFull = (m_nReadPos == m_nWritePos);
			assert(m_nReadPos <= m_nBufSize);
			assert(m_nWritePos <= m_nBufSize);
			return count;
		}
		else       // 剩余空间不足
		{
			// 先填充满剩余空间，再回头找空间存放
			memcpy(m_pBuf + m_nWritePos, buf, leftcount);
			m_nWritePos =
					(m_nReadPos >= count - leftcount) ?
							count - leftcount : m_nReadPos;
			memcpy(m_pBuf, buf + leftcount, m_nWritePos);
			m_bFull = (m_nReadPos == m_nWritePos);
			assert(m_nReadPos <= m_nBufSize);
			assert(m_nWritePos <= m_nBufSize);
			return leftcount + m_nWritePos;
		}
	}
	else
	{
		/*                          == 内存模型 ==
		 (unread)                 (read)                     (unread)
		 |-------------------|----------------------------|---------------------------|
		 m_nWritePos    (leftcount)    m_nReadPos
		 */
		int leftcount = m_nReadPos - m_nWritePos;
		if (leftcount > count)
		{
			// 有足够的剩余空间存放
			memcpy(m_pBuf + m_nWritePos, buf, count);
			m_nWritePos += count;
			m_bFull = (m_nReadPos == m_nWritePos);
			assert(m_nReadPos <= m_nBufSize);
			assert(m_nWritePos <= m_nBufSize);
			return count;
		}
		else
		{
			// 剩余空间不足时要丢弃后面的数据
			memcpy(m_pBuf + m_nWritePos, buf, leftcount);
			m_nWritePos += leftcount;
			m_bFull = (m_nReadPos == m_nWritePos);
			assert(m_bFull);
			assert(m_nReadPos <= m_nBufSize);
			assert(m_nWritePos <= m_nBufSize);
			return leftcount;
		}
	}
}

/************************************************************************/
/* 从缓冲区读数据，返回实际读取的字节数                                 */
/************************************************************************/
int CCycleBuffer::Read(char* buf, int count)
{
	if (count <= 0)
		return 0;
	m_bFull = false;
	if (m_bEmpty)       // 缓冲区空，不能继续读取数据
	{
		return 0;
	}
	else if (m_nReadPos == m_nWritePos)   // 缓冲区满时
	{
		/*                          == 内存模型 ==
		 (data)          m_nReadPos                (data)
		 |--------------------------------|--------------------------------------------|
		 m_nWritePos         m_nBufSize
		 */
		int leftcount = m_nBufSize - m_nReadPos;
		if (leftcount > count)
		{
			memcpy(buf, m_pBuf + m_nReadPos, count);
			m_nReadPos += count;
			m_bEmpty = (m_nReadPos == m_nWritePos);
			return count;
		}
		else
		{
			memcpy(buf, m_pBuf + m_nReadPos, leftcount);
			m_nReadPos =
					(m_nWritePos > count - leftcount) ?
							count - leftcount : m_nWritePos;
			memcpy(buf + leftcount, m_pBuf, m_nReadPos);
			m_bEmpty = (m_nReadPos == m_nWritePos);
			return leftcount + m_nReadPos;
		}
	}
	else if (m_nReadPos < m_nWritePos)   // 写指针在前(未读数据是连接的)
	{
		/*                          == 内存模型 ==
		 (read)                 (unread)                      (read)
		 |-------------------|----------------------------|---------------------------|
		 m_nReadPos                m_nWritePos                     m_nBufSize
		 */
		int leftcount = m_nWritePos - m_nReadPos;
		int c = (leftcount > count) ? count : leftcount;
		memcpy(buf, m_pBuf + m_nReadPos, c);
		m_nReadPos += c;
		m_bEmpty = (m_nReadPos == m_nWritePos);
		assert(m_nReadPos <= m_nBufSize);
		assert(m_nWritePos <= m_nBufSize);
		return c;
	}
	else          // 读指针在前(未读数据可能是不连接的)
	{
		/*                          == 内存模型 ==
		 (unread)                (read)                      (unread)
		 |-------------------|----------------------------|---------------------------|
		 m_nWritePos                  m_nReadPos                  m_nBufSize

		 */
		int leftcount = m_nBufSize - m_nReadPos;
		if (leftcount > count)   // 未读缓冲区够大，直接读取数据
		{
			memcpy(buf, m_pBuf + m_nReadPos, count);
			m_nReadPos += count;
			m_bEmpty = (m_nReadPos == m_nWritePos);
			assert(m_nReadPos <= m_nBufSize);
			assert(m_nWritePos <= m_nBufSize);
			return count;
		}
		else       // 未读缓冲区不足，需回到缓冲区头开始读
		{
			memcpy(buf, m_pBuf + m_nReadPos, leftcount);
			m_nReadPos =
					(m_nWritePos >= count - leftcount) ?
							count - leftcount : m_nWritePos;  // 计算剩余未读数据大小
			memcpy(buf + leftcount, m_pBuf, m_nReadPos); // 注意目的指针位置
			m_bEmpty = (m_nReadPos == m_nWritePos);
			assert(m_nReadPos <= m_nBufSize);
			assert(m_nWritePos <= m_nBufSize);
			return leftcount + m_nReadPos;
		}
	}
}

/************************************************************************/
/* 获取缓冲区有效数据长度                                               */
/************************************************************************/
int CCycleBuffer::GetLength()
{
	if (m_bEmpty)
	{
		return 0;
	}
	else if (m_bFull)
	{
		return m_nBufSize;
	}
	else if (m_nReadPos < m_nWritePos)
	{
		return m_nWritePos - m_nReadPos;
	}
	else
	{
		return m_nBufSize - m_nReadPos + m_nWritePos;
	}
}

void CCycleBuffer::Empty()
{
	m_nReadPos = 0;
	m_nWritePos = 0;
	m_bEmpty = true;
	m_bFull = false;
}

bool CCycleBuffer::isEmpty()
{
	return m_bEmpty;
}

bool CCycleBuffer::isFull()
{
	return m_bFull;
}

/*
 * main.cpp
 *
 *  Created on: 2013-5-27
 *      Author: shiguang
 */

#include "CCycleBuffer.h"

int main()
{
	CCycleBuffer buffer(100);
	char* datachar = new char[40];
	char* reschar = new char[100];

	int res = 0;

	for (int i = 0; i < 40; ++i)
	{
		datachar[i] = i + 1;
	}
	res = buffer.Write(datachar, 40);
	printf("写入数据个数：%d\n", res);
	res = buffer.Write(datachar, 40);
	printf("写入数据个数：%d\n", res);
	res = buffer.Write(datachar, 40);
	printf("写入数据个数：%d\n", res);
	res = buffer.Write(datachar, 40);
	printf("写入数据个数：%d\n", res);

	res = buffer.Read(reschar, 100);
	printf("读取数据个数：%d\n", res);
	for (int i = 0; i < 100; ++i)
	{
		if (i % 10 == 0)
		{
			printf("\n");
		}
		printf("%2d   ", reschar[i]);
	}

	return 0;
}

输出结果：

写入数据个数：40
写入数据个数：40
写入数据个数：20
写入数据个数：0
读取数据个数：100

 1    2    3    4    5    6    7    8    9   10   
11   12   13   14   15   16   17   18   19   20   
21   22   23   24   25   26   27   28   29   30   
31   32   33   34   35   36   37   38   39   40   
 1    2    3    4    5    6    7    8    9   10   
11   12   13   14   15   16   17   18   19   20   
21   22   23   24   25   26   27   28   29   30   
31   32   33   34   35   36   37   38   39   40   
 1    2    3    4    5    6    7    8    9   10   
11   12   13   14   15   16   17   18   19   20   

源程序来自网络资料！