1.简单示意图如下
2.实现代码
#ifndef CACHE_H_
#define CACHE_H_
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#define CACHESIZE (/*8 * 10*/24)//1M
class Cache
{
public:
Cache();
~Cache();
//得到缓存中当前数据量
int getsize();
//插入数据pdata:数据指针 len:数据大小 返回:成功0 失败-1
int insert(char *pdata, int len);
//取出数据data:数据缓存指针 len:取数据大小 返回:成功0 失败-1
int popup(char *data, int len);
private:
//判断缓存是否已满
bool b_full;
//插入指针
char *in_ptr;
//取数据指针
char *ou_ptr;
//缓存尾指针
char *end_pointer;
private:
//缓存
char cache_buffer[CACHESIZE];
};
#endif
#include"Cache.h"
Cache::Cache()
{
memset(cache_buffer, 0, CACHESIZE);
b_full = false;
in_ptr = cache_buffer;
ou_ptr = cache_buffer;
end_pointer = cache_buffer + (CACHESIZE - 1);
}
Cache::~Cache()
{
}
int Cache::getsize()
{
int data_size;
if (b_full) {
data_size = CACHESIZE;
}
else {
data_size = in_ptr - ou_ptr >= 0 ? in_ptr - ou_ptr : CACHESIZE - (ou_ptr - in_ptr);
}
return data_size;
}
int Cache::insert(char *pdata, int len)
{
if (NULL == pdata || len <= 0 || b_full){
return -1;
}
int all_left, right_left;
all_left = ou_ptr - in_ptr > 0 ? ou_ptr - in_ptr : CACHESIZE - (in_ptr - ou_ptr);
if (len > all_left) {
return -1;
}
right_left = ou_ptr - in_ptr > 0 ? ou_ptr - in_ptr : end_pointer - in_ptr + 1;
if (len > right_left) {
memcpy(in_ptr, pdata, right_left);
in_ptr = cache_buffer;
memcpy(in_ptr, pdata + right_left, len - right_left);
in_ptr += (len - right_left);
}
else if (len == right_left)
{
if (in_ptr - ou_ptr > 0) {
memcpy(in_ptr, pdata, right_left);
in_ptr = cache_buffer;
}else {
memcpy(in_ptr, pdata, right_left);
in_ptr += right_left;
}
}else {
memcpy(in_ptr, pdata, len);
in_ptr += len;
}
if (in_ptr == ou_ptr)
b_full = true;
return 0;
}
int Cache::popup(char *data, int len)
{
if (NULL == data || len <= 0) {
return -1;
}
int data_size, right_size;
if (b_full) {
data_size = CACHESIZE;
}
else {
data_size = in_ptr - ou_ptr >= 0 ? in_ptr - ou_ptr : CACHESIZE - (ou_ptr - in_ptr);
}
if (len > data_size) {
return -1;
}
right_size = in_ptr - ou_ptr > 0 ? in_ptr - ou_ptr : end_pointer - ou_ptr + 1;
if (len > right_size) {
memcpy(data, ou_ptr, right_size);
ou_ptr = cache_buffer;
memcpy(data + right_size, ou_ptr, len - right_size);
ou_ptr += (len - right_size);
}
else if (len == right_size)
{
if (ou_ptr - in_ptr > 0) {
memcpy(data, ou_ptr, right_size);
ou_ptr = cache_buffer;
}else {
memcpy(data, ou_ptr, right_size);
ou_ptr += right_size;
}
}else {
memcpy(data, ou_ptr, len);
ou_ptr += len;
}
b_full = false;
return 0;
}
