SEQUENTIAL FILE ORGANISATION

SEQUENTIAL FILE ORGANISATION

Following code explains the concept of sequential access file:

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

Program for performing various operations on Sequential File organisation.

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

#include<iostream.h>

#include<iomanip.h>

#include<fstream.h>

#include<string.h>

#include<conio.h>

#include<stdlib.h>

class EMP_CLASS

{

 typedef struct EMPLOYEE

 {

char name[10];

int emp_id;

int salary;

 }Rec;

 Rec Records;

public:

void Create();

void Display();

void Update();

void Delete();

void Append();

int Search();

};

void EMP_CLASS::Create()

{

char ch='y';

fstream seqfile;

seqfile.open("EMP.DAT",ios::in|ios::out|ios::binary);

do

{

cout<<"\n Enter Name: ";

cin>>Records.name;

cout<<"\n Enter Emp_ID: ";

cin>>Records.emp_id;

cout<<"\n Enter Salary: ";

cin>>Records.salary;

//then write the record containing this data in the file

seqfile.write((char*)&Records,sizeof(Records));

cout<<"\nDo you want to add more records?";

cin>>ch;

}while(ch=='y');

seqfile.close();

}

void EMP_CLASS::Display()

{

fstream seqfile;

int n,m,i;

seqfile.open("EMP.DAT",ios::in|ios::out|ios::binary);

//positioning the pointer in the file at the beginning

seqfile.seekg(0,ios::beg);

cout<<"\n The Contents of file are ..."<<endl;

//read the records sequentially

while(seqfile.read((char *)&Records,sizeof(Records)))

{

if(Records.emp_id!=-1)

{

cout<<"\nName: "<<Records.name;

cout<<"\nEmp_ID: "<<Records.emp_id;

cout<<"\nSalary: "<<Records.salary;

cout<<"\n";

}

 }

 int last_rec=seqfile.tellg();//last record position

//formula for computing total number of  objects in the file

 n=last_rec/(sizeof(Rec));

 cout<<"\n\n Total number of objects are "<<n<<"(considering logical deletion)";

 seqfile.close();

}

void EMP_CLASS::Update()

{

int pos;

cout<<"\n For updation,";

fstream seqfile;

seqfile.open("EMP.DAT",ios::in|ios::out|ios::binary);

seqfile.seekg(0,ios::beg);

//obtaining the position of desired record in the file

pos=Search();

if(pos==-1)

{

cout<<"\n The record is not present in the file";

return;

}

//calculate the actual offset of the desired record in the file

int offset=pos*sizeof(Rec);

seqfile.seekp(offset);//seeking the desired record for modification

cout<<"\n Enter the values for updation...";

cout<<"\n Name: ";cin>>Records.name;

cout<<"\n Emp_Id: ";cin>>Records.emp_id;

cout<<"\n Salary: ";cin>>Records.salary;

seqfile.write((char*)&Records,sizeof(Records))<<flush;

seqfile.seekg(0);

seqfile.close();

cout<<"\n The record is updated!!!";

}

void EMP_CLASS::Delete()

{

int id,pos;

cout<<"\n For deletion,";

fstream seqfile;

seqfile.open("EMP.DAT",ios::in|ios::out|ios::binary);

seqfile.seekg(0,ios::beg);//seeking for reading purpose

pos=Search();//finding pos. for the record to be deleted

if(pos==-1)

{

cout<<"\n The record is not present in the file";

return;

}

//calculate offset to locate the desired record in the file

int offset=pos*sizeof(Rec);

seqfile.seekp(offset);//seeking the desired record for deletion

strcpy(Records.name,"");

Records.emp_id=-1;

Records.salary=-1;

seqfile.write((char*)&Records,sizeof(Records))<<flush;

seqfile.seekg(0);

seqfile.close();

cout<<"\n The record is Deleted!!!";

}

void EMP_CLASS::Append()

{

fstream seqfile;

seqfile.open("EMP.DAT",ios::ate|ios::in|ios::out|ios::binary);

seqfile.seekg(0,ios::beg);

int i=0;

while(seqfile.read((char *)&Records,sizeof(Records)))

{

i++;//going through all the records

// for reaching at the end of the file

}

//instead of above while loop

//we can also use seqfile.seekg(0,ios::end)

//for reaching at the end of the file

seqfile.clear();//turning off EOF flag

cout<<"\n Enter the record for appending";

cout<<"\nName: ";cin>>Records.name;

cout<<"\nEmp_ID: ";cin>>Records.emp_id;

cout<<"\nSalary: ";cin>>Records.salary;

seqfile.write((char*)&Records,sizeof(Records));

seqfile.seekg(0);//reposition to start(optional)

seqfile.close();

cout<<"\n The record is Appended!!!";

}

int EMP_CLASS::Search()

{

fstream seqfile;

int id,pos;

cout<<"\n Enter the Emp_ID for searching the record ";

cin>>id;

seqfile.open("EMP.DAT",ios::ate|ios::in|ios::out|ios::binary);

seqfile.seekg(0,ios::beg);

pos=-1;

int i=0;

while(seqfile.read((char *)&Records,sizeof(Records)))

{

if(id==Records.emp_id)

{

pos=i;

break;

}

i++;

}

return pos;

}

void main()

{

EMP_CLASS List;

char ans='y';

int choice,key;

clrscr();

do

{

cout<<"\n             Main Menu             "<<endl;

cout<<"\n 1.Create";

cout<<"\n 2.Display";

cout<<"\n 3.Update";

cout<<"\n 4.Delete";

cout<<"\n 5.Append";

cout<<"\n 6.Search";

cout<<"\n 7.Exit";

cout<<"\n Enter your choice ";

cin>>choice;

switch(choice)

{

case 1:List.Create();

break;

case 2:List.Display();

break;

case 3:List.Update();

break;

case 4:List.Delete();

break;

case 5:List.Append();

break;

case 6:key=List.Search();

if(key<0)

cout<<"\n Record is not present in the file";

else

cout<<"\n Record is present in the file";

break;

case 7:exit(0);

}

cout<<"\n\t Do you want to go back to Main Menu?";

cin>>ans;

}while(ans=='y');

}

Please ask for explanation if you face any problem in understanding the code.It is better to understand than just copying and running a code.