比如针对下面的这样一个协议：

(资料图片)

数据在发送时涉及到一个大小端的概念，大小端是针对多字节数据的传输，比如上述协议中字段1，假设两字节内容为0x0001，先发送0x01后发送0x00，称为小端模式；先发送0x00后发送0x01，称为大端模式。

假设字段1内容为0x001，字段2内容为0x40533333(对应为3.3)

假设按照小端方式发送，下面是帧数据：

55 AA 01 00 33 33 53 40 ED

下面来看看如何解析：

#includeintmain(){unsignedcharRxbuf[9]={0x55,0xAA,0x01,0x00,0x33,0x33,0x53,0x40,0xED};shortDeviceId;floatVoltage;unsignedcharcheck=0;inti;for(i=0;i<8;i++){check^=Rxbuf[i];}if(Rxbuf[0]==0x55&&Rxbuf[1]==0xAA&&Rxbuf[8]==check){DeviceId=(Rxbuf[3]<<8)|Rxbuf[2];Voltage=*((float*)&Rxbuf[4]);printf("DeviceId:%d\n",DeviceId);printf("Voltage:%f\n",Voltage);}return0;}

简单来说就是硬来，按照数组的先后顺序逐个重组解析，如果协议比较长，代码里会充斥着很多的数组下标，一不小心就数错了。而且如果更改协议的话，代码要改动很多地方。

后来有人告诉我可以定义个结构体，然后使用memcpy函数直接复制过去就完事了。

#include#include#pragmapack(1)structRxFrame{unsignedcharheader1;unsignedcharheader2;shortdeviceId;floatvoltage;unsignedcharcheck;};intmain(){unsignedcharRxbuf[9]={0x55,0xAA,0x01,0x00,0x33,0x33,0x53,0x40,0xED};structRxFrameRxData;unsignedcharcheck=0;inti;for(i=0;i<8;i++){check^=Rxbuf[i];}memcpy(&RxData,Rxbuf,sizeof(Rxbuf));if(Rxbuf[0]==0x55&&Rxbuf[1]==0xAA&&RxData.check==check){printf("DeviceId:%d\n",RxData.deviceId);printf("Voltage:%f\n",RxData.voltage);}return0;}

再后来，又见到有人用如下代码实现：

#include#include"convert.h"intmain(){unsignedcharRxbuf[9]={0x55,0xAA,0x01,0x00,0x33,0x33,0x53,0x40,0xED};shortDeviceId;floatVoltage;unsignedcharcheck=0;inti;intindex=0;for(i=0;i<8;i++){check^=Rxbuf[i];}if(Rxbuf[0]==0x55&&Rxbuf[1]==0xAA&&Rxbuf[8]==check){index+=2;ByteToShort(Rxbuf,&index,&DeviceId);ByteToFloat(Rxbuf,&index,&Voltage);printf("DeviceId:%d\n",DeviceId);printf("Voltage:%f\n",Voltage);}return0;}

#ifndefCONVERT_H#defineCONVERT_HvoidShortToByte(unsignedchar*dest,int*index,shortvalue);voidFloatToByte(char*dest,int*index,floatvalue);#endif//CONVERT_H

#include"convert.h"#include#includestaticboolEndianflag=0;voidByteToShort(constunsignedchar*source,int*index,short*result){inti,len=sizeof(short);charp[len];memset(p,0,len);if(Endianflag==1){for(i=0;i

#ifndefCONVERT_H#defineCONVERT_HvoidByteToShort(constunsignedchar*source,int*index,short*result);voidByteToInt(unsignedchar*source,int*index,int*result);voidByteToLong(char*source,int*index,longlong*result);voidByteToFloat(unsignedchar*source,int*index,float*result);voidByteToDouble(unsignedchar*source,int*index,double*result);voidByteToString(unsignedchar*source,int*index,char*result,intlength);voidShortToByte(unsignedchar*dest,int*index,shortvalue);voidIntToByte(char*dest,int*index,intvalue);voidLongToByte(char*dest,int*index,longlongvalue);voidFloatToByte(char*dest,int*index,floatvalue);voidDoubleToByte(unsignedchar*dest,int*index,doublevalue);voidStringToByte(char*dest,int*index,intlength,char*value);#endif//CONVERT_H