结构体校验码异常

yky189

于 2024-12-10 22:40:15 发布

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文章标签： C 结构体数据对齐

本文链接：https://blog.youkuaiyun.com/yky189/article/details/144385618

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调试的时候，发现加在结构体后面的校验码总是不对，在此做个笔记。

问题出在结构体对齐上，虽然校验码在最后的位置，但是由于结构体对齐的问题，实际结构体是4字节对齐，会在最后面补上2字节。所以在计算结构体校验码的时候做法是减去最后两个校验码，但是校验码并不在这里，而是更前面的2个字节，所以就会出现，在第一次算完校验码，写入后，在读取在算校验码，就不对了。因为第一次计算算入了刚才的校验码结果作为校验数据

typedef struct
{  
  alarmParamStruct_int32_t cellOverVoltage;
  alarmParamStruct_int32_t cellUnderVoltage;
  alarmParamStruct_int32_t totalOverVoltage;
  alarmParamStruct_int32_t totalUnderVoltage;
  alarmParamStruct_int32_t dischargeOverTemperature;
  alarmParamStruct_int32_t chargeOverTemperature;
  alarmParamStruct_int32_t MOSTemperatureOver;
//  alarmParamStruct_int32_t envirenmentOver;
//  alarmParamStruct_int32_t envirenmentUnder;
  alarmParamStruct_int32_t dischargeUnderTemperature;
  alarmParamStruct_int32_t chargeUnderTemperature;
//  alarmParamStruct_int32_t SOCOver;
//  alarmParamStruct_int32_t SOCUnder;
  alarmParamStruct_int32_t dischargeOverCurrent;
  alarmParamStruct_int32_t chargeOverCurrent;
  alarmParamStruct_uint16_t envirenmentOver;
  alarmParamStruct_uint16_t envirenmentUnder;
  alarmParamStruct_uint16_t SOCOver;
  alarmParamStruct_uint16_t SOCUnder;
  alarmParamStruct_uint16_t voltageDiff;
  uint16_t sumCheck;
}alarmParamSettingStruct;

uint16_t length = sizeof(AlarmParmStruct);
AlarmParmStruct.sumCheck = crc16((uint8_t*)&AlarmParmStruct,length-2);

为了让校验码在最后两个字节，需要在它前面手动补齐2字节，作为占位符。

typedef struct
{  
  alarmParamStruct_int32_t cellOverVoltage;
  alarmParamStruct_int32_t cellUnderVoltage;
  alarmParamStruct_int32_t totalOverVoltage;
  alarmParamStruct_int32_t totalUnderVoltage;
  alarmParamStruct_int32_t dischargeOverTemperature;
  alarmParamStruct_int32_t chargeOverTemperature;
  alarmParamStruct_int32_t MOSTemperatureOver;
//  alarmParamStruct_int32_t envirenmentOver;
//  alarmParamStruct_int32_t envirenmentUnder;
  alarmParamStruct_int32_t dischargeUnderTemperature;
  alarmParamStruct_int32_t chargeUnderTemperature;
//  alarmParamStruct_int32_t SOCOver;
//  alarmParamStruct_int32_t SOCUnder;
  alarmParamStruct_int32_t dischargeOverCurrent;
  alarmParamStruct_int32_t chargeOverCurrent;
  alarmParamStruct_uint16_t envirenmentOver;
  alarmParamStruct_uint16_t envirenmentUnder;
  alarmParamStruct_uint16_t SOCOver;
  alarmParamStruct_uint16_t SOCUnder;
  alarmParamStruct_uint16_t voltageDiff;
  uint16_t alignUse;
  uint16_t sumCheck;
}alarmParamSettingStruct;

这样得到的结果就对了，最后2为是校验码。

00> 191~crc16=51658;data=0**
00> 192~crc16=19085;data=244**
00> 193~crc16=36026;data=1**
00> 194~crc16=14635;data=0**
00> 195~crc16=11158;data=0**
00> 196~crc16=38650;data=0**
00> 197~crc16=63860;data=0**
00> 198~crc16=30230;data=0**
00> 199~crc16=38711;data=0**
00> #################
00> length=200**
00> 191~crc16=51658;data=0**
00> 192~crc16=19085;data=244**
00> 193~crc16=36026;data=1**
00> 194~crc16=14635;data=0**
00> 195~crc16=11158;data=0**
00> 196~crc16=38650;data=0**
00> 197~crc16=63860;data=0**
00> 198~crc16=63143;data=55**
00> 199~crc16=9797;data=151**
00> *****************
00> length=200**
00> 191~crc16=51658;data=0**
00> 192~crc16=19085;data=244**
00> 193~crc16=36026;data=1**
00> 194~crc16=14635;data=0**
00> 195~crc16=11158;data=0**
00> 196~crc16=38650;data=0**
00> 197~crc16=63860;data=0**
00> 198~crc16=63143;data=55**
00> 199~crc16=9797;data=151**