Deleting a Record From a File

[Alvi89]

Im currently trying to delete a record from a file
The structure ive used is this:

struct studentRecord
{
		char rollnumber[12];
		char name[32];
		int attendancePercentage;
		float quiz;
		float assignment;
		int classpart;
		float mid1;
		float mid2;
		float final;
		float semesterPerformance;
		float overallPerformance;

	};

Now I have 2 problems:
1.I cant copy the name of 1 record to another
2. if i comment the name and roll number the file that is rewritten does not contain ANY data.
ANY kind of help would be greatly appreciated, i have been stuck on this for the past 2 hours

Here is my code

//Function for deleting a record
void deleteRecord(char filename[])
{
		char choice ='y';
		cout <<endl<<endl;
		cout <<"Please enter the roll number or Name of the student for the  \nRecord to be deleted" <<endl;
		char searchWord[32];
		gets (searchWord);
		gets (searchWord);
		int RecordNum = searchDisplay("Student Records.bin", searchWord); //Returns the record number to be deleted
		cout<<endl<<endl<<"DO U WISH TO DELETE THIS RECORD? Y/N" <<endl;
		cin >> choice;
		if (choice == 'y' || choice =='Y')
		{
			//We first load all the file data to the Memory
			FILE *inFile;
			inFile = fopen("Student Records.bin" , "a+");
				if (inFile == NULL) {
				printf("Cannot open %s\n", filename);
				exit(8);
				}
			int noRecords = NumberRecords("Student Records.bin");
			studentRecord* Record;
			Record = (studentRecord *) malloc(noRecords*sizeof(studentRecord));
			if (Record == NULL) {fputs ("Memory error",stderr); exit (2);}
			for(int j=0; j < noRecords;j++)
			{
				fread((void*)&Record[j].rollnumber , sizeof(studentRecord), 1, inFile);
			}
			//Then we swap records untill last record has been reached.
			for (int x=0; x <= (noRecords-RecordNum);x++)
			{
				//last record cant be swapped so we insert a check
				if(noRecords == RecordNum)
					break;

				/*strcpy_s ( Record[RecordNum + x].name, Record[RecordNum + (x+1)].name );
				strcpy_s ( Record[RecordNum + x].rollnumber, Record[RecordNum + (x+1)].rollnumber );*/
				Record[RecordNum + x].attendancePercentage = Record[RecordNum + (x+1)].attendancePercentage;
				Record[RecordNum + x].quiz = Record[RecordNum + (x+1)].quiz;
				Record[RecordNum + x].assignment = Record[RecordNum + (x+1)].assignment;
				Record[RecordNum + x].classpart= Record[RecordNum + (x+1)].classpart;
				Record[RecordNum + x].mid1= Record[RecordNum + (x+1)].mid1;
				Record[RecordNum + x].mid2= Record[RecordNum + (x+1)].mid2;
				Record[RecordNum + x].final= Record[RecordNum + (x+1)].final;
				Record[RecordNum + x].semesterPerformance= Record[RecordNum + (x+1)].semesterPerformance;
				Record[RecordNum + x].overallPerformance= Record[RecordNum + (x+1)].overallPerformance;


			}
			//Now we rewrite all our data back to the file.
			FILE *infile;
			infile = fopen("Student Records.bin" , "w");
			if (infile == NULL) {
			printf("Cannot open %s\n", filename);
			exit(8);}
				
			for(int f=0; f < noRecords - 1; f++)
			{
							fwrite((void*)&Record[f].rollnumber , sizeof(studentRecord), 1, inFile);
			}
			fclose(inFile);
free(Record);

			
		}
}

[Adak]

You probably don't want to delete a record - shocking I know. Simply zero out the main key (perhaps an ID number which can never be zero), and the last name, first letter, to an end of string char: '\0'. (It's strlen() will be 0 in that case)

You actually would like to keep about 10-20% of your array empty, and available for new record data. When the array data is loaded, your program should simply count the number of valid records. If the empty records rises above 20-25%, then it can compress the database back to 10%, if space and/or run time performance, is critical - otherwise, don't worry about it.

Your print and display functions need the adjustment made to them, (an if statement), so they don't display any invalid records, that have been "deleted" in this manner.

As far as moving data, have you tried:

temp is a local struct (because you did prototype your struct above main() in global space right?)

Then just a simple swap may work:

temp = yourStruct[i];
structArray[i] = structArray[i+1];
structArray[i+1] = temp;

If you have objects that need to be allocated, the above swap won't work as is, so always test it well.