环形队列实现

在实际应用中，环形队列通常用在只能buffer固定大小数据量的场景，如audio driver.

在buffer数据时，有一个writePointer来记录上层app往buffer写的位置，用一个readPointer来记录audio driver读的位置。

#include <string.h>
#include <stdio.h>
#define RING_BUF_SIZE 10
typedef struct _RingBuffer{
　　int _data[RING_BUF_SIZE];
　　int _writePointer;
　　int _readPointer;
　　int _size;
}RingBuffer;
void ringBuffer_init(RingBuffer *pRingBuffer)
{
　　memset(pRingBuffer->_data, 0 ,sizeof(pRingBuffer->_data));
　　pRingBuffer->_writePointer = 0;
　　pRingBuffer->_readPointer = 0;
　　pRingBuffer->_size = 0;
}

void ringBuffer_write(RingBuffer *pRingBuffer, int *data, int len)
{
　　if (pRingBuffer->_size + len > RING_BUF_SIZE)
　　{
　　　　printf("ring buffer full ");
　　　　return ;
　　}
　　int newWritePointer = 0;
　　int loop = 0;
　　newWritePointer = pRingBuffer->_writePointer + len;
　　if (newWritePointer >= RING_BUF_SIZE)
　　{
　　　　newWritePointer -= RING_BUF_SIZE;
　　　　loop = 1;
　　}
　　if (loop)
　　{
　　　　memcpy(pRingBuffer->_data + pRingBuffer->_writePointer, data, (RING_BUF_SIZE - pRingBuffer->_writePointer)*sizeof(int));
　　　　memcpy(pRingBuffer->_data, data + RING_BUF_SIZE - pRingBuffer->_writePointer, (len - (RING_BUF_SIZE - pRingBuffer->_writePointer))*sizeof(int));
　　}
　　else
　　{
　　　　memcpy(pRingBuffer->_data + pRingBuffer->_writePointer, data, len*sizeof(int));
　　}
　　pRingBuffer->_size += len;
　　pRingBuffer->_writePointer = newWritePointer;
}

void ringBuffer_read(RingBuffer *pRingBuffer, int *data, int len)
{
　　if (len > pRingBuffer->_size)
　　{
　　　　printf("no enough data ");
　　　　return;
　　}
　　int newReadPointer = 0;
　　int loop = 0;
　　newReadPointer = pRingBuffer->_readPointer + len;
　　if (newReadPointer >= RING_BUF_SIZE)
　　{
　　　　newReadPointer -= RING_BUF_SIZE;
　　　　loop = 1;
　　}
　　if (loop)
　　{
　　　　memcpy(data, pRingBuffer->_data + pRingBuffer->_readPointer,(RING_BUF_SIZE - pRingBuffer->_readPointer)*sizeof(int));
　　　　memcpy(data + RING_BUF_SIZE - pRingBuffer->_readPointer, pRingBuffer->_data, (len - (RING_BUF_SIZE - pRingBuffer->_readPointer))*sizeof(int));
　　}
　　else
　　{
　　memcpy(data, pRingBuffer->_data + pRingBuffer->_readPointer, len * sizeof(int));
　　}
　　pRingBuffer->_size -= len;
　　pRingBuffer->_readPointer = newReadPointer;
}
int main(int argc, char **argv)
{
　　int writeData1[6] = {0,1,2,3,4,5};
　　int writeData2[6] = {6,7,8,9,10,11};
　　int readData[4];
　　RingBuffer _ringBuffer;
　　ringBuffer_init(&_ringBuffer);
　　ringBuffer_write(&_ringBuffer, writeData1, 6);
　　printf("wp:%d, rp:%d, sz:%d ", _ringBuffer._writePointer, _ringBuffer._readPointer, _ringBuffer._size);
　　int idx = 0;
　　for (idx = _ringBuffer._readPointer; idx < _ringBuffer._writePointer; idx++)
　　{
　　　　printf("data after write:%d ", _ringBuffer._data[idx]);
　　}
　　ringBuffer_read(&_ringBuffer, readData, 4);
　　for (idx = _ringBuffer._readPointer; idx < _ringBuffer._writePointer; idx++)
　　{
　　　　printf("data after read:%d ", _ringBuffer._data[idx]);
　　}
　　printf("wp:%d, rp:%d, sz:%d ", _ringBuffer._writePointer, _ringBuffer._readPointer, _ringBuffer._size);
　　for (idx = 0; idx < 4; idx++)
　　{
　　　　printf("read data:%d ", readData[idx]);
　　}
　　ringBuffer_write(&_ringBuffer, writeData2, 6);
　　printf("wp:%d, rp:%d, sz:%d ", _ringBuffer._writePointer, _ringBuffer._readPointer, _ringBuffer._size);

　　for (idx = _ringBuffer._readPointer; idx < RING_BUF_SIZE; idx++)
　　{
　　　　printf("data after write:%d ", _ringBuffer._data[idx]);
　　}

　　for (idx = 0; idx < _ringBuffer._writePointer; idx++)
　　{
　　　　printf("data after write:%d ", _ringBuffer._data[idx]);
　　}
　　return 0;
}

运行结果如下：