Strategy（策略模式）

1、定义

    定义一系列的算法，把他们一个个封装起来，并且使他们可以相互替换。使得算法可以独立与使用它的客户而改变。

2、结构图

3、协作角色：

          Strategy 定义所支持算法的接口。

          ConcreteStrategy 具体算法

          Context 用一个ConcreteStrategy对象来配置，维护一个对Strategy对象的引用。可定义一个接口来让Strategy 访问它的数据。

4、适用性

       1、客户不注重算法的实现细节

       2、许多相关的类仅仅有行为的差距

5、实例

    1、需求，一段数据在传输过程中，可能有很多种校验方式，CRC、校验和、或者别的。

    2、结构图，先不画了。

    3、实现：

 context.h

#ifndef __CONTEXT_H__#define __CONTEXT_H__typedef enum {CHECK_SUM,CRC16,}CHECK_ALG;#define SEND_DATA_MAX_LEN 256typedef struct {CHECK_ALG alg;int (*check_alg)(char*, unsigned int); int check_val;int len;char *data;}context;int checksum(char *data, unsigned int len);int CRC_16(char *data, unsigned int len);int config_alg(context *ctx);int calc_check_val(context *ctx);#endif

 

context.c

#include <stdio.h>#include "context.h"int config_alg(context *ctx){if(NULL == ctx)return -1;switch(ctx->alg){case CHECK_SUM:ctx->check_alg = checksum;break;case CRC16:ctx->check_alg = CRC_16;break;default:break;}return 0;}int calc_check_val(context *ctx){if((NULL != ctx)&&(NULL != ctx->data)&&(NULL != ctx->check_alg))ctx->check_val = ctx->check_alg(ctx->data, ctx->len);elsereturn -1;return 0;}

 

checksum.c

#include <stdio.h>#include "context.h"int checksum(char *data, unsigned int len){char sum;unsigned int i;printf("via %s\n",__func__);sum = 0;for(i = 0; i < len; i++){sum += data[i];}return (-sum);}

CRC16.c

#include <stdio.h>#include "context.h"unsigned short const crc16_table[256] = {0x0000, 0xC0C1, 0xC181, 0x0140, 0xC301, 0x03C0, 0x0280, 0xC241,0xC601, 0x06C0, 0x0780, 0xC741, 0x0500, 0xC5C1, 0xC481, 0x0440,0xCC01, 0x0CC0, 0x0D80, 0xCD41, 0x0F00, 0xCFC1, 0xCE81, 0x0E40,0x0A00, 0xCAC1, 0xCB81, 0x0B40, 0xC901, 0x09C0, 0x0880, 0xC841,0xD801, 0x18C0, 0x1980, 0xD941, 0x1B00, 0xDBC1, 0xDA81, 0x1A40,0x1E00, 0xDEC1, 0xDF81, 0x1F40, 0xDD01, 0x1DC0, 0x1C80, 0xDC41,0x1400, 0xD4C1, 0xD581, 0x1540, 0xD701, 0x17C0, 0x1680, 0xD641,0xD201, 0x12C0, 0x1380, 0xD341, 0x1100, 0xD1C1, 0xD081, 0x1040,0xF001, 0x30C0, 0x3180, 0xF141, 0x3300, 0xF3C1, 0xF281, 0x3240,0x3600, 0xF6C1, 0xF781, 0x3740, 0xF501, 0x35C0, 0x3480, 0xF441,0x3C00, 0xFCC1, 0xFD81, 0x3D40, 0xFF01, 0x3FC0, 0x3E80, 0xFE41,0xFA01, 0x3AC0, 0x3B80, 0xFB41, 0x3900, 0xF9C1, 0xF881, 0x3840,0x2800, 0xE8C1, 0xE981, 0x2940, 0xEB01, 0x2BC0, 0x2A80, 0xEA41,0xEE01, 0x2EC0, 0x2F80, 0xEF41, 0x2D00, 0xEDC1, 0xEC81, 0x2C40,0xE401, 0x24C0, 0x2580, 0xE541, 0x2700, 0xE7C1, 0xE681, 0x2640,0x2200, 0xE2C1, 0xE381, 0x2340, 0xE101, 0x21C0, 0x2080, 0xE041,0xA001, 0x60C0, 0x6180, 0xA141, 0x6300, 0xA3C1, 0xA281, 0x6240,0x6600, 0xA6C1, 0xA781, 0x6740, 0xA501, 0x65C0, 0x6480, 0xA441,0x6C00, 0xACC1, 0xAD81, 0x6D40, 0xAF01, 0x6FC0, 0x6E80, 0xAE41,0xAA01, 0x6AC0, 0x6B80, 0xAB41, 0x6900, 0xA9C1, 0xA881, 0x6840,0x7800, 0xB8C1, 0xB981, 0x7940, 0xBB01, 0x7BC0, 0x7A80, 0xBA41,0xBE01, 0x7EC0, 0x7F80, 0xBF41, 0x7D00, 0xBDC1, 0xBC81, 0x7C40,0xB401, 0x74C0, 0x7580, 0xB541, 0x7700, 0xB7C1, 0xB681, 0x7640,0x7200, 0xB2C1, 0xB381, 0x7340, 0xB101, 0x71C0, 0x7080, 0xB041,0x5000, 0x90C1, 0x9181, 0x5140, 0x9301, 0x53C0, 0x5280, 0x9241,0x9601, 0x56C0, 0x5780, 0x9741, 0x5500, 0x95C1, 0x9481, 0x5440,0x9C01, 0x5CC0, 0x5D80, 0x9D41, 0x5F00, 0x9FC1, 0x9E81, 0x5E40,0x5A00, 0x9AC1, 0x9B81, 0x5B40, 0x9901, 0x59C0, 0x5880, 0x9841,0x8801, 0x48C0, 0x4980, 0x8941, 0x4B00, 0x8BC1, 0x8A81, 0x4A40,0x4E00, 0x8EC1, 0x8F81, 0x4F40, 0x8D01, 0x4DC0, 0x4C80, 0x8C41,0x4400, 0x84C1, 0x8581, 0x4540, 0x8701, 0x47C0, 0x4680, 0x8641,0x8201, 0x42C0, 0x4380, 0x8341, 0x4100, 0x81C1, 0x8081, 0x4040};int CRC_16(char *data, unsigned int len){unsigned short crc;printf("via %s\n",__func__);while(len--){crc = (crc >> 8) ^ crc16_table[(crc ^ (*data++)) & 0xff];}}

 

client.c

#include <stdio.h>#include <string.h>#include "context.h"#define DATA_LEN10int main(){unsigned int i;context ctx;memset((void *)&ctx, 0, sizeof(context));char buffer[DATA_LEN];char ret;for(i = 0; i < DATA_LEN; i++){  buffer[i] = i;}ctx.alg = CHECK_SUM;ctx.data = buffer;ctx.len = DATA_LEN;if(-1 == config_alg(&ctx))return -1;if(-1 == calc_check_val(&ctx))return -2;printf("first check val is %d\n",ctx.check_val);ctx.alg = CRC16;if(-1 == config_alg(&ctx))return -3;if(-1 == calc_check_val(&ctx))return -4;printf("Second check val is %d\n",ctx.check_val);return 0;}