返回空指针和其他问题

如何解决返回空指针和其他问题

我要发布这四个功能，因为它们彼此关联。我在理解如何将它们彼此连接时遇到了麻烦。我的输入文件如下

*****这只是一个helper.c文件。从单独的驱动程序文件中读取main（）。从逻辑上讲这是正确的，因此不需要帮助。

* 2. Creating it again should cause an existence error
*
CREATE VEHICLE vehicle.dat 17 5
* Open it
OPEN VEHICLE vehicle.dat
*
* 3. Insert some vehicles
*
INSERT VEHICLE CB001,CHEVY,BelAir,1957
PRINTALL VEHICLE vehicle.dat
INSERT VEHICLE DD001,DODGE,Dart,1970
PRINTALL VEHICLE vehicle.dat
*
* 4. Read an existing vehicle
*
READ VEHICLE CB001
*
* 5. Read should not find these two vehicles
READ VEHICLE TP001
READ VEHICLE FE001

这只是一个片段，但是当我执行程序时，会出现这些奇怪的错误。由于已经是冗长的帖子，因此不会完全发布，但是这些都是这些错误

fread并未读取应有的记录我的逻辑看起来在vehicleInsert / vehicleRead函数中对我来说是正确的，但是什么都不给我。

我将发布的一个错误是奇怪的，它在打印所有记录时是这样的。

 >> PRINTALL VEHICLE vehicle.dat
MaxHash=19,RecSize=36,MaxProbes=5
87 ▒}▒   12                          Hash=12
100 ▒}▒    5                        Hash=12

因此，我不确定这是否是寻求帮助的正确地点，但这使我发疯。我从逻辑上相信，我缺少一些东西。

/*
This function reads a record at the specified RBN in the specified file.

•Determine the RBA based on iRBN and pHashFile->hashHeader.iRecSize.
•Use fseek to position the file in that location.
•Use fread to read that record and return it through pRecord.
•If the location is not found,return RC_LOC_NOT_FOUND.  
Otherwise,return RC_OK.
•Note: if the location is found,that does NOT imply that a vehicle was written to that location.
Why?

*/
int readRec(HashFile *pHashFile,int iRBN,void *pRecord){

// • Determine the RBA based on iRBN and pHashFile->hashHeader.iRecSize.
int RBA;
int RC;
RBA = iRBN * pHashFile->hashHeader.iRecSize;
Vehicle tempVeh;

// •Use fseek to position the file in that location.
fseek(pHashFile->pFile,RBA,SEEK_CUR);
RC = fread(&tempVeh,pHashFile->hashHeader.iRecSize,1,pHashFile->pFile);
printf("readRec RC:%d\n",RC);
if (RC != 1){
    return RC_LOC_NOT_FOUND;
}else {
    return RC_OK;
}
}

/*
This function writes a record to the specified RBN in the specified file. 
•Determine the RBA based on iRBN and pHashFile->hashHeader.iRecSize.
•Use fseek to position the file in that location.
•Use fwrite to write that record to the file.
•If the fwrite fails,return RC_LOC_NOT_WRITTEN.  
Otherwise,return RC_OK

*/
int writeRec(HashFile *pHashFile,SEEK_CUR);

RC = fwrite(&tempVeh,pHashFile->pFile);
printf("RC CODE IN writeRec:%d\n",RC);
if(RC != 1){
    return RC_LOC_NOT_WRITTEN;
}else {
    return RC_OK;
}

// •If the fwrite fails,return RC_LOC_NOT_WRITTEN.  
// Otherwise,return RC_OK
}

/*

This function inserts a vehicleinto the specified file.
•Determine the RBN using the driver's hash function.
•Use readRec to read the record at that RBN.  
•If that location doesn't exist or the record at that location has a szVehicleId[0] == '\0':
Write this new  vehicl erecord at that location using writeRec.
•If that record exists and that vehicle's szVehicleId matches,return RC_REC_EXISTS.  (Do not update it.)
•Otherwise,return RC_SYNONYM.

INSERT VEHICLE DD001,1970
vehicleInsert(&hashFile,&vehicle);
readRec(HashFile *pHashFile,void *pRecord)
writeRec(HashFile*pHashFile,void *pRecord)

*/


int vehicleInsert(HashFile *pHashFile,Vehicle *pVehicle){
// This function inserts a vehicle into the specified file.
// •Determine the RBN using the driver's hash function.
//      hash(vehicle.szVehicleId,hashFile.hashHeader.iMaxHash);
int RBN;
int RC;
Vehicle matchesVehcileID;
RBN = hash(pVehicle->szVehicleId,pHashFile->hashHeader.iMaxHash);

// •Use readRec to read the record at that RBN.  
RC = readRec(pHashFile,RBN,&matchesVehcileID);
printf("RC CODE IN INSERT for readRec:%d\n",RC);

// •If that location doesn't exist or the record at that location has a szVehicleId[0] == '\0':
// Write this new  vehicl erecord at that location using writeRec.
    if(RC == RC_LOC_NOT_FOUND || pVehicle->szVehicleId[0] == '\0'){
        int rc1;
        rc1 = writeRec(pHashFile,pVehicle);
        printf("rc1 in vehicleInsert:%d\n",rc1 );
        printf("PRINTING: vehicleInsert is WRITING\n");
    } else if
// •If that record exists and that vehicle's szVehicleId matches,return RC_REC_EXISTS.  (Do not update it.)
    (RC == RC_REC_EXISTS && strcmp(pVehicle->szVehicleId,matchesVehcileID.szVehicleId)){
        return RC_REC_EXISTS;
        printf("PRINTING RC REC exists\n");
    } else
    {
        return RC_SYNONYM;
    }

}

/*

This function reads the specified vehicle by its szVehicleId.
•Since pVehicle->szVehicleId was provided,determine the RBN using the driver's hash function.
•Be able to return that RBN via the third parameter.
•Use readRec to read the record at that RBN. 
•Ifthe vehicleat that location matches the specified szVehicleId,return the vehiclevia pVehicleand return RC_OK.
•Otherwise,return RC_REC_NOT_FOUND

*/

int vehicleRead(HashFile *pHashFile,Vehicle *pVehicle,int *piRBN){
// •Since pVehicle->szVehicleId was provided,determine the RBN using the driver's hash function.
int RBN;
Vehicle matchesVehcileID;
RBN = hash(pVehicle->szVehicleId,pHashFile->hashHeader.iMaxHash);

// •Be able to return that RBN via the third parameter.
*piRBN = RBN;

// •Use readRec to read the record at that RBN. 
readRec(pHashFile,&matchesVehcileID);

// •If the vehicle at that location matches the specified szVehicleId,return the vehicle via pVehicle and return RC_OK.
// •Otherwise,return RC_REC_NOT_FOUND


    if(strcmp(pVehicle->szVehicleId,matchesVehcileID.szVehicleId)){
        writeRec(pHashFile,&pVehicle);
        return RC_OK;
    }else {
        return RC_REC_NOT_FOUND;
    }



}

返回空指针和其他问题

如何解决返回空指针和其他问题

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