Chapter 1, Problem 6PA

Program Plan Intro

Extended Case Study for removing an existing record from file:

Program plan:

• Include the required header files in your program.
• Define a class “Personal” with the following functions.
  • Define the default constructor “Personal()” that initializes the member variables.
  • Define the constructor “Personal()” with arguments that initializes the member variables.
  • Define the function “writeToFile()” to write a record to the output stream.
  • Define the function “writeNullToFile()” to write a null record to the output stream.
  • Define the function “readFromFile()” to read a record from the input stream.
  • Define the function “readKey()” to read SSN from console.
  • Define the function “size()” to get the size of a record.
  • Define the function “operator==()” to check the equality of the two records.
  • Define the function “isNull()” to check the current record is deleted record.
  • Define the function “writeLegibly()” to write a record to the output stream.
  • Define the function “operator<<()” to write a record to the output stream.
  • Define the function “readFromConsole()” to read a record from the input stream.
  • Define the function “operator>>()” to read a record from the output stream.
• Define a class “Student” with the following functions.
  • Define the default constructor “Student()” that initializes the member variables.
  • Define the constructor “Student()” with arguments that initializes the member variables.
  • Define the function “writeToFile()” to write a record to the output stream.
  • Define the function “writeNullToFile()” to write a null record to the output stream.
  • Define the function “readFromFile()” to read a record from the input stream.
  • Define the function “size()” to get the size of a record.
  • Define the function “writeLegibly()” to write a record to the output stream.
  • Define the function “operator<<()” to write a record to the output stream.
  • Define the function “readFromConsole()” to read a record from the input stream.
  • Define the function “operator>>()” to read a record from the output stream.
  • Define the function “isNull()” to check the current record is deleted record.
• Define a class “Database” with the following functions.
  • Define the default constructor “Database()” that initializes the member variables.
  • Define the function “run()” that processes the user wishes.
  • Define the function “add()” to add a record to the database.
  • Define the function “find()” to find a record in the database.
  • Define the function “modify()” to modify the existing record.
  • Define the function “remove()” to delete an existing record.
  • Define the function “operator<<()” to write the database to the output stream.
  • Define the function “print()” to display the database.
• Define the function “main()”.
  • Create a database for “Personal” and call the function “run()”.

Program Description Answer

/**********************************************************

* This program Extends the case study for removing an     *

* existing record.                                        *

**********************************************************/

Explanation of Solution

Program:

//personal.h.

#ifndef PERSONAL

#define PERSONAL

// Include the required header files

#include<iostream>

#include <fstream>

#include <cstring>

using namespace std;

//Personal class declaration.

class Personal

{

//Access Specifier.

public:

//constructor.

Personal();

//Argumented constructor.

Personal(char*,char*,char*,int,long);

//Function to write Person data to file.

void writeToFile(fstream&) const;

//Function to write null record to file.

void writeNullToFile(fstream&) ;

//Function to read Person data from file.

void readFromFile(fstream&);

//Function read SSN

void readKey();

//Function to determine record is null

bool isNull();

//Function that returns the size of a record.

int size() const

{

//Sum all the fields length and return it.

return 9 + nameLen + cityLen + sizeof(year) + sizeof(salary);

}

/*Function to check the passed the record is equal to the current record.*/

bool operator==(const Personal& pr) const

{

//Compare the SSN's of current record and pr.

/*If they equal the function return true. otherwise it return false.*/

return strncmp(pr.SSN,SSN,9) == 0;

}

//Access specifier.

protected:

//Declare variables.

const int nameLen, cityLen;

char SSN[10], *name, *city;

int year;

long salary;

//Function to write the record to the output stream.

ostream& writeLegibly(ostream&);

/*Overload the operator << to write to the output stream.*/

friend ostream& operator<<(ostream& out, Personal& pr)

{

//Call the member function to write.

return pr.writeLegibly(out);

}

//Function to read a record from the input stream.

istream& readFromConsole(istream&);

/*Overload the operator >> to read fromo the input stream.*/

friend istream& operator>>(istream& in, Personal& pr)

{

//Call the member function to read.

return pr.readFromConsole(in);

}

};

#endif

//personal.cpp

//Include the header files.

#include "personal.h"

//Constructor that fixes the length for name and city.

Personal::Personal() : nameLen(10), cityLen(10)

{

/*Create the character array for name and city with specified size.*/

name = new char[nameLen+1];

city = new char[cityLen+1];

}

//Constructor with input arguments.

Personal::Personal(char *ssn, char *n, char *c, int y, long s) :

nameLen(10), cityLen(10)

{

/*Create the character array for name and city with specified size.*/

name = new char[nameLen+1];

city = new char[cityLen+1];

//Copy the passed SSN

strcpy(SSN,ssn);

//Copy the name.

strcpy(name,n);

//Copy the city.

strcpy(city,c);

//store the year.

year = y;

//Store the salary.

salary = s;

}

//Function to write the record into the output stream.

void Personal::writeToFile(fstream& out) const

{

//Write the SSN.

out.write(SSN,9);

//Write the name.

out.write(name,nameLen);

//Write the city.

out.write(city,cityLen);

/*Convert the year into char* and write it on the output.*/

out.write(reinterpret_cast<const char*>(&year),sizeof(int));

/*Convert the salary into char* and write it on the output.*/

out.write(reinterpret_cast<const char*>(&salary),sizeof(int));

}

//Function to write the null record into the output stream.

void Personal::writeNullToFile(fstream& out)

{

/* First Character of the SSN should be marked with '#'*/

SSN[0]='#';

//Write the SSN.

out.write(SSN,9);

//Write the name.

out.write(name,nameLen);

//Write the city.

out.write(city,cityLen);

/*Convert the year into char* and write it on the output.*/

out.write(reinterpret_cast<const char*>(&year),sizeof(int));

/*Convert the salary into char* and write it on the output.*/

out.write(reinterpret_cast<const char*>(&salary),sizeof(int));

}

//Function to read a record from the input stream.

void Personal::readFromFile(fstream& in)

{

//Read the SSN

in.read(SSN,9);

//Read the name.

in.read(name,nameLen);

//Read the city.

in.read(city,cityLen);

//Convert the char* to int and store it in year.

in.read(reinterpret_cast<char*>(&year),sizeof(int));

//Convert the char* to int and store it in salary.

in.read(reinterpret_cast<char*>(&salary),sizeof(int));

}

//Function to read the SSN from the user.

void Personal::readKey()

{

//Declare the variables.

char s[80];

//Prompt the user.

cout << "Enter SSN: ";

//Read the SSN

cin.getline(s,80);

//copy the SSN.

strncpy(SSN,s,9);

}

//Function to check record is null.

bool Personal::isNull()

{

/*Return true if SSN[0] is '#', otherwise return false */

  return SSN[0]=='#';

}

//Function to write the record to the console.

ostream& Personal::writeLegibly(ostream& out)

{

//Terminate the strings.

SSN[9] = name[nameLen] = city[cityLen] = '\0';

//Write SSN, name, year, city, salary to the console.

out << "SSN = " << SSN << ", name = " << name<< ", city = " << city << ", year = " << year<< ", salary = " << salary;

//Return the output stream.

return out;

}

//Function to read a record from the console.

istream& Personal::readFromConsole(istream& in)

{

//Terminate the strings.

SSN[9] = name[nameLen] = city[cityLen] = '\0';

char s[80];

//Read SSN in variable 's'.

cout << "SSN: ";

in.getline(s,80);

//Copy the SSN from 's'.

strncpy(SSN,s,9);

//Read name in variable 's'.

cout << "Name: ";

in.getline(s,80);

//Copy the name from 's'.

strncpy(name,s,nameLen);

//Read the city in 's'.

cout << "City: ";

in.getline(s,80);

//Copy the city from 's'.

strncpy(city,s,cityLen);

//Read the year.

cout << "Birthyear: ";

in >> year;

//Read the salary.

cout << "Salary: ";

in >> salary;

in.ignore();

//Return the input stream.

return in;

}

//student.h

//Defining the header file.

#ifndef STUDENT

#define STUDENT

//Include the header file

#include "personal.h"

//Derive the class Student from Personal

class Student : public Personal

{

//Access specifier.

public:

//Constructor

Student();

//Constructor with arguments*/

Student(char*,char*,char*,int,long,char*);

//Function to write record to the output stream.

void writeToFile(fstream&) const;

//Function to write null record to file.

void writeNullToFile(fstream&) ;

//Function to read a Student record from input stream.

void readFromFile(fstream&);

//Function to get the size of the Student record.

int size() const

{

/*Call the base call method to find the record size.*/

return Personal::size() + majorLen;

}

//Function to determine record is null

bool isNull();

//Access specifier.

protected:

//Declare variables.

char *major;

const int majorLen;

//Function to write the record to the output stream.

ostream& writeLegibly(ostream&);

/*Overaloaded operator << to write to the output stream.*/

friend ostream& operator<<(ostream& out, Student& sr)

{

//Call member function to write the record.

return sr.writeLegibly(out);

}

//Function to read a record from the input stream.

istream& readFromConsole(istream&);

/*Overload the operator >> to read fromo the input stream.*/

friend istream& operator>>(istream& in, Student& sr)

{

//Call the member function to read.

return sr.readFromConsole(in);

}

};

#endif

//student.cpp

//Include the header files.

#include "student.h"

//Constructor to initialize the variables.

Student::Student() : majorLen(10)

{

//Call base call constructor for initialization.

Personal();

//Create the character array for the major.

major = new char[majorLen+1];

}

//Constructor to initialize all the variables. This constructor takes arguments*/

Student::Student(char *ssn, char *n, char *c, int y, long s, char *m) :

majorLen(11)

{

//Call baseclass constructor.

Personal(ssn,n,c,y,s);

//Create the character array for the major.

major = new char[majorLen+1];

//Copy the major.

strcpy(major,m);

}

//Function to write the record to the output stream.

void Student::writeNullToFile(fstream& out) 

{

/*Call base class method to write the name, city, SSN, year, salary.*/

Personal::writeNullToFile(out);

//Write the major.

out.write(major,majorLen);

}

//Function to write the record to the output stream.

void Student::writeToFile(fstream& out) const

{

/*Call base class method to write the name, city, SSN, year, salary.*/

Personal::writeToFile(out);

//Write the major.

out.write(major,majorLen);

}

//Function to read a record from the input stream.

void Student::readFromFile(fstream& in)

{

/*Call baseclass method to read the name,city, SSN,  year,salary.*/

Personal::readFromFile(in);

//Read the major.

in.read(major,majorLen);

}

/*Function to write the student record to the output stream.*/

ostream& Student::writeLegibly(ostream& out)

{

/*Call baseclass method to write the name,city, SSN,  year,salary.*/

Personal::writeLegibly(out);

major[majorLen] = '\0';

//Write the major.

out << ", major = " << major;

//Return the output stream.

return out;

}

//Function to read a record from the input stream console.

istream& Student::readFromConsole(istream& in)

{

/*Call base class method to read name, city, year, SSN, salary from console.*/

Personal::readFromConsole(in);

char s[80];

//Prompt the user to enter the major.

cout << "Major: ";

//read the major in variable 's'.

in.getline(s,80);

//Copy the major from 's'.

strncpy(major,s,9);

//Return the input stream.

return in;

}

//Function to check record is null.

bool Student::isNull()

{

//Call base class method to check the record is null.

  return Personal::isNull();

}

//database.h

//Define the header file.

#ifndef DATABASE

#define DATABASE

//Create the template class.

template<class T>

//Create the class Database

class Database

{

//Access Specifier.

public:

//Construtor.

Database();

//Destructor

~Database();

/*Function that displays the menu and proceeds as per user wish.*/

void run();

//Access Specifier.

private:

/* Declare variables*/

fstream database;

char fName[20];

//Function to display the database

ostream& print(ostream&);

//Function to add a record into the database.

void add(T&);

/*Function to find a particular record in the database.*/

bool find(const T&);

//Function to modify the record in the database.

void modify(const T&);

//Function to delete the record from the database.

void remove(const T&);

/*Overloaded operator << to print the given database to the output stream.*/

friend ostream& operator<<(ostream& out, Database& db)

{

//Call the method to print the database.

return db.print(out);

}

};

#endif

//database.cpp

//Include the header files.

#include <iostream>

#include <vector>

#include "student.h"

#include "personal.h"

#include "database.h"

//No argumented constructor.

template<class T>

Database<T>::Database() {}

//Destructor

template<class T>

Database<T>::~Database()

{

//Declare the variables.

T tmp;

/*Create temporary file */

fstream tmpFile;

tmpFile.open("tmp1.txt",ios::in|ios::out|ios::binary|ios::trunc );

//Open the database.

database.open(fName,ios::in|ios::out|ios::binary);

/*Check database is null. If so exit from the loop.*/

if (database.eof())

//Exit from the loop.

exit(1);

/*Infinite loop that runs until record is inserted in the database.*/

while (true)

  {

//Read a record from the file.

tmp.readFromFile(database);

/*Check database is null. If so exit from the loop.*/

if (database.eof())

//Exit from the loop.

break;

  //Otherwise write record to the tmpFile.

else if(!tmp.isNull())

{

  //write record to the tmpFile.

  tmp.writeToFile(tmpFile);

}

  }

//Close tmpFile

tmpFile.close();

//Close database

database.close();

//Open the database.

database.open("student.txt",ios::in|ios::out|ios::binary | ios::trunc );

//Open the tmp1.txt

tmpFile.open("tmp1.txt", ios::in| ios::out| ios::binary );

/*Inifinite loop that runs until record is inserted in the database.*/

while (true)

{

//Read a record from the file.

tmp.readFromFile(tmpFile);

/*Check tmpFile is null. If so exit from the loop.*/

if (tmpFile.eof())

//Exit from the loop.

break;

//Write the valid record to the file.

tmp.writeToFile(database);

  }

//Close tmpFile

tmpFile.close();

//Close database

database.close();

//Rename the new file.

rename("tmp1.txt", fName);

}

//Function to add a record into the database.

template<class T>

void Database<T>::add(T& d)

{

//Open the database.

database.open(fName,ios::in|ios::out|ios::binary);

//Goto the file end.

database.seekp(0,ios::end);

//Write 'd' to the database.

d.writeToFile(database);

//Close the database.

database.close();

}

//Function to modify the existing record in the database.

template<class T>

void Database<T>::modify(const T& d)

{

//Declare the variable.

T tmp;

//Open the database.

database.open(fName,ios::in|ios::out|ios::binary);

//Repeated search until database is null.

while(!database.eof())

{

//Read the record from the database.

tmp.readFromFile(database);

//Check tmp matches d.

if (tmp == d)

{

//Read the record

cin >> tmp;

//Seek to the record's position.

database.seekp(-d.size(),ios::cur);

//Write the record to the file.

tmp.writeToFile(database);

//Close the database.

database.close();

//Exit from the function.

return;

  }

  }

//Close the database.

database.close();

//Print the message indicating record not found.

cout << "The record to be modified is not in the database\n";

}

//Function to modify the existing record in the database.

template<class T>

void Database<T>::remove(const T& d)

{

//Declare the variable.

T tmp;

//Open the database.

database.open(fName,ios::in|ios::out|ios::binary);

//Repeated search until database is null.

while(!database.eof())

{

  //Read the record from the database.

  tmp.readFromFile(database);

  //Check tmp matches d.

  if (tmp == d)

  {

  //Seek to the record's position.

  database.seekp(-d.size(),ios::cur);

  //Write the record to the file.

  tmp.writeNullToFile(database);

  //Close the database.

  database.close();

  //Exit from the function.

  return;

  }

  }

  //Close the database.

  database.close();

  //Print the message indicating record not found.

cout << "The record to be deleted is not in the database\n";

}

//Function to find the given record in the database.

template<class T>

bool Database<T>::find(const T& d)

{

//Declare the variable.

T tmp;

//Open the database.

database.open(fName,ios::in|ios::binary);

while(!database.eof())

{

//Read the record from the database.

tmp.readFromFile(database);

//Check tmp matches d.

if (tmp == d)

{

//Close the database.

database.close();

//Record found, so return true.

return true;

  }

}

//Close the database.

database.close();

//Record not found, so return false.

return false;

}

template<class T>

ostream& Database<T>::print(ostream& out)

{

//Declare the variable.

T tmp;

//Open the database.

database.open(fName,ios::in|ios::binary);

//Infinite loop.

while (true)

{

//Read a record from the file.

tmp.readFromFile(database);

/*Check database is null. If so exit from the loop.*/

if (database.eof())

//Exit from the loop.

break;

//Write the record tmp to the output stream.

out << tmp << endl;

  }

//Close the database.

database.close();

//Return the output stream.

return out;

}

//Function to process the user wish.

template<class T>

void Database<T>::run()

{

//Get the database filename.

cout << "File name: ";

cin >> fName;

//Declare variables.

char option[5];

T rec;

//Display menu.

cout << "1. Add 2. Find 3. Modify a record; 4. Remove a record 5. Exit\n";

//Get option.

cout << "Enter an option: ";

cin.getline(option,4);

//Infinite loop ends until user wishes to exit.

while (cin.getline(option,4))

{

//If user wants to add a record.

if (*option == '1')

  {

//Get the record.

cin >> rec;

//Write the record into the database.

add(rec);

  }

//If user wants to find a record,

else if (*option == '2')

  {

//Read the SSN

rec.readKey();

//Display record is found or not.

cout << "The record is ";

//Check finding record returns false.

if (find(rec) == false)

  cout << "not ";

  cout << "in the database\n";

  }

/*If user wants to modify a record in the database,*/

else if (*option == '3')

{

//Read the SSN of the record to be modified.

rec.readKey();

//Call the method modify()

modify(rec);

  }

/*If user wants to remove a record in the database,*/

else if (*option == '4')

{

//Read the SSN of the record to be modified.

rec.readKey();

//Call the method remove()

remove(rec);

  }

//If user enters wrong option.

else if (*option != '5')

//Print wrong input.

cout << "Wrong option\n";

//Otherwise exit from the loop.

else

//Return to the main function.

return;

//Display the database.

cout << *this;

//Ask the user for an option.

cout << "Enter an option: ";

  }

}

//main() method.

int main()

{

/*Creating the database with Personal objects and call the function run().*/

Database<Personal>().run();

//To pause the console window.

system("pause");

  return 0;

}

Sample Output

Output:

File name: student.txt

1. Add 2. Find 3. Modify a record; 4. Remove a record 5. Exit

Enter an option: 1

SSN: 101

Name: Arlen

City: Delhi

Birthyear: 2005

Salary: 80000

SSN = 101, name = Arlen, city = Delhi, year = 2005, salary = 80000

Enter an option: 1

SSN: 002

Name: Akash

City: Calcutta

Birthyear: 2001

Salary: 10000

SSN = 101, name = Arlen, city = Delhi, year = 2005, salary = 80000

SSN = 002, name = Akash, city = Calcutta, year = 2001, salary = 10000

Enter an option: 4

Enter SSN: 002

SSN = 101, name = Arlen, city = Delhi, year = 2005, salary = 80000

SSN = #02, name = Akash, city = Calcutta, year = 2001, salary = 10000

Enter an option: 5

Press any key to continue . . .

After running of the program, the file has been changed as follows,

student.txt: