Need help with little things...

[donfrema]

So I have gotten the basis of this down... I just need to add a few more things but I am unsure about how to do this. I don't know how I would go about deleting a file? Also... whenever I try to display the ID, it doesn't appear/work. So If I typed in information... Then went to display is (Since its the first one I'd choose Student ID # 1) and it would come back with invalid data? Any Idea why? Thanks!

#include <iostream>
#include <fstream>
#include <string>

using namespace std;


struct Student  {
	
	int   id;			// Student ID
	char  name[30];		// Student Name
	int   points;	    // Points earned 
	float gpa;		    // GPA
};

int getOption () {
	int selection;
	cout << "Options :\n";
	cout << "1) Initialize the student file\n";
	cout << "2) Add a new student\n";
	cout << "3) Display a student\n";
	cout << "4) Update a student\n";
	cout << "5) End\n\b";
	cout << "Please select an option : ";
	cin >> selection;
	while (selection < 1 || selection > 5) 	{
		cout << "Please select a number between 1-5\n";
		cin >> selection;
	}
	return selection;
}

void UpdateStudent(fstream &fileStudents)  {
	Student student;
	long recNum;
	// Get the Student ID to change
	cout << "Enter the student ID that you want to change:";
	cin >> recNum;
	// Move to the record and read it.
	fileStudents.seekg(recNum * sizeof(student), ios::beg);
	fileStudents.read(reinterpret_cast<char *>(&student),
		           sizeof(student));
	// Display the record contents
	cout << "Name : ";
	cout << student.name << endl;
	cout << "Points Earned : ";
	cout << student.points << endl;
	cout << "GPA : ";
	cout << student.gpa << endl;
	// Get the new record data.
	cout << "Begin entering the new student data :\n";
	cout << "Name : ";
	cin.ignore();
	cin.getline(student.name, 30);
	cout << "Points Earned : ";
	cin >> student.points;
	cout << "GPA : ";
	cin >> student.gpa;
	
	// Set position to start of the student record
	fileStudents.seekp(recNum * sizeof(student), ios::beg);
	fileStudents.write(reinterpret_cast<char *>(&student),
		            sizeof(student));
	
}

void DisplayStudent(fstream &fileStudents) {
	Student student;
	long id;
	// Get the student ID to display
	cout << "Enter the student ID to view ";
	cin >> id;
	// Move to the record and read it.
	fileStudents.seekg(id * sizeof(student), ios::beg);
	fileStudents.read(reinterpret_cast<char *>(&student), sizeof(student));
	// Show the student's data
	cout << "ID           : ";
	cout << student.id << endl;
	cout << "Name         : ";
	cout << student.name << endl;
	cout << "Points earned: ";
	cout << student.points << endl;
	cout << "GPA          : ";
	cout << student.gpa << endl;
	
}

void AddStudent(fstream &fileStudents) {
	cout << "Please enter the Student information : \n";
	Student student;
	
	cout << "Name : ";
	cin.ignore();
	cin.getline(student.name, 30);
	cout << "Points earned : ";
	cin >> student.points;
	cout << "GPA : ";
	cin >> student.gpa;
	
	
	fileStudents.write(reinterpret_cast<char *>(&student),
		            sizeof(student));
	
}

void InitializeStudentFile(fstream &fileStudents) {
	Student student = {0, " ", 0, 0.0};
	for (int id = 0; id < 100; id++) {
		fileStudents.write(reinterpret_cast<char *>(&student), sizeof(student));
	}
	
}


int main(int argc, char * argv[]) {	
	int option;
	// Create a random access file and initialize with 100 empty records
	fstream fileStudents ("Students.dat", ios::out | ios::binary);
	

	do	{
		
		option = getOption();
		switch (option) {
	      case 1: InitializeStudentFile(fileStudents);
			break;
		  case 2: AddStudent(fileStudents);
			break;
		  case 3: DisplayStudent(fileStudents);
			break;
		  case 4: UpdateStudent(fileStudents);
			break;
		  case 5: cout << "bye\n";
		}
	}  while (option != 5);

	fileStudents.close();
	return 0;
}

[JLBorges]

> I don't know how I would go about deleting a file?

Perhaps you just want overwrite a file, discarding its previous contents.

std::ofstream file( "file_name" ) ; 
// this creates a new file if the file does not exist
// otherwise it truncates the existing file to an empty file.  

Ideally, when you want to perform only input, as in DisplayStudent(), use a std::ifstream. For only output, as in AddStudent(), use a std::ofstream.



> whenever I try to display the ID, it doesn't appear/work.
> ... and it would come back with invalid data? Any Idea why?

See: http://cplusplus.com/forum/general/69685/#msg372532

[donfrema]

Overwriting a file won't do anything good for me.

I need to be able to remove a record from the list of records I already have.
This means that I could add record 101, then I need to delete it by pressing 6 and then selecting that Student ID 101. Then it no longer exists.

I fixed it so that it would actually tell you the record number when adding a person. Now All I need to do is be able to remove that person from the record.

[JLBorges]

> Overwriting a file won't do anything good for me.
> I need to be able to remove a record from the list of records I already have.

a. Read all the records in the file into memory.

b. Overwrite the file record by record, skipping the record that you want to remove.

[Danishx83]

I think

JLBorges

has pointed a good option because if at any time you have a problem/crash in the program may result in a damaged file. So a better way could be
open file
Read all data and sort it
suggestion :-
Student studentContainer[MAX_LIMIT];
read each and place studentContainer[recNum] in the array
close the file

Work on your data

now if a Student at recNum is removed, then you may replace it with a empty

Student empty;
empty.id = 0;
void RemoveStudent(Student studentContainer[]; int recNum){
  studentContainer[recNum] = empty;
}
bool StudentEmpty(Student studentContainer[]; int recNum){
  if(studentContainer[recNum] == empty)
    return 1;
  else
    return 0;
}

now use it in Display, Add, Update Student

if (StudentEmpty(studentContainer[],recNum))
  //what you want to do if the record is empty
else
  //what if record is there 

when finished open file
overwrite the file with all new data
close the file