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.
