Basic file operations CBSE class xii ln 7

BASIC FILE OPERATIONS
IN BINARY FILES

Introduction
 The only difference is that while working with binary files, you do
need to prefix file modes with ios::binary at the time of opening the
file.
 You have learnt how to create files (open them in ios::out or ios::app
mode which will create a file if it doesn't exist already),
 To read records from binary files (call read() function through
stream object to which file is attached),
 To write records in binary files (call write() function through stream
object which file is attached).

BASIC OPERATIONS IN A BINARY FILE
Searching
Appending data
Inserting data in sorted file
Modifying data
Deleting a record

Searching in a file
 We can perform search in a binary file opened in input mode by
reading each record then checking whether it is our desired record
or not.
 For instance, if you want to search for a record for a student having
rollno as 1 in file marks.dat, you can implement this search process in
C++ in two manners :
with records implemented through structures.
with records implemented through classes.

#include<fstream.h>
#include<conio.h>
#include<stdlib.h>
class student
{
int rollno;
char name[20];
char branch[3];
float marks;
char grade;
public:
void getdata()
{
cout<<"Rollno: ";
cin>>rollno;
cout<<"Name: ";
cin>>name;
cout<<"Branch: ";
cin>>branch;
cout<<"Marks: ";
cin>>marks;
if(marks>=75)
grade = 'A';
else if(marks>=60)
grade = 'B';
else if(marks>=50)
grade = 'C';
else if(marks>=40)
grade = 'D';
else
grade = 'F';
}
void putdata()
{
cout<<"Rollno: "<<rollno<<"tName: "<<name<<"n";
cout<<"Marks: "<<marks<<"tGrade: "<<grade<<"n";
}
int getrno()
{
return rollno;
}
} stud1;
// class student created

//Example : To search a record in a file
void main()
{
clrscr();
fstream fio("marks.dat", ios::in | ios::out);
char ans='y';
while(ans=='y' || ans=='Y')
{
stud1.getdata();
fio.write((char *)&stud1, sizeof(stud1));
cout<<"Record added to the filen";
cout<<"nWant to enter more ? (y/n)..";
cin>>ans;
}
clrscr();
int rno;
long pos;
char found='f';
cout<<"Enter rollno of student to be search for: ";
cin>>rno;
fio.seekg(0);
while(!fio.eof())
{
pos=fio.tellg();
fio.read((char *)&stud1, sizeof(stud1));
if(stud1.getrno() == rno)
{
stud1.putdata();
fio.seekg(pos);
found='t';
break;
}
}
if(found=='f')
{
cout<<"nRecord not found in the file..!!n";
cout<<"Press any key to exit...n";
getch();
exit(2);
}
fio.close();
getch();
}

Appending Data in C++
 To append data in a file, the file is opened with the
following two specifications :
file is opened in output mode
file is opened in ios::app mode
 Once the file gets opened in ios::app mode, the previous
records/information is retained and new data gets
appended to the file.

// Example : to append data in a file in C++
class student
{
:// class definition
} stud1;
void main()
{
clrscr();
ofstream fout("marks.dat", ios::app);
char ans='y';
while(ans=='y' || ans=='Y')
{
stud1.getdata();
fout.write((char *)&stud1, sizeof(stud1));
cout<<"Data appended in the file successfully..!!n";
cout<<"nWant to enter more ? (y/n)..";
cin>>ans;
}
fout.close();
cout<<"nPress any key to exit...n";
getch();
}

Inserting Data in Sorted File
 To insert data in a sorted file, firstly, its appropriated position
is determined
 and then records in the file prior to this determined position
are copied to temporary file,
 followed by the new record to be inserted and then the rest
of the records from the file are also copied.

Inserting Data in Sorted File
STEPS :
(Open the file in read mode(marks.dat) and open temp.dat in write mode)
 i) Determining the appropriate position.
 (ii) Copy the records prior to determined position to a temporary file say
temp.dat.
 (iii) Append the new record in the temporary file temp.dat.
 (iv) Now append the rest of the records in temporary file temp.dat.
 (v) Delete the file marks.dat by using the following code.
remove("marks.dat");
 (vi) Now, rename the file temp.dat as marks.dat as follows :
rename("temp.dat", "marks.dat");

//EXAMPLE to insert a new record in a sorted file
class student
{
: // class definition
} stud1;
void main()
{
clrscr();
ifstream fin("marks.dat", ios::in);
ofstream fout("temp.dat", ios::out);
char last='y';
cout<<"Enter details of student whose record is
to be insertedn";
stud1.getdata();
while(!fin.eof())
{
fin.read((char *)&stud, sizeof(stud));
if(stud1.getrno()<=stud.getrno())
{
fout.write((char *)&stud1,
sizeof(stud1));
last = 'n';
break; }
else
{
fout.write((char *)&stud, sizeof(stud));
} }
if(last == 'y')
{ fout.write((char *)&stud1, sizeof(stud1)); }
else if(!fin.eof())
{
while(!fin.eof())
{
fin.read((char *)&stud, sizeof(stud));
fout.write((char *)&stud, sizeof(stud));
} }
fin.close();
fout.close();
fin.open("marks.dat", ios::in);
cout<<"File now contains:n";
while(!fin.eof())
{ fin.read((char *)&stud, sizeof(stud));
if(fin.eof())
{
break;
}
stud.putdata();
}
fin.close();
getch();
}

Deleting a record from a File
STEPS :
To delete a record, following procedure is carried out :
 (i) Firstly, determine the position of the record to be deleted, by performing
a search in the file.
 (ii) Keep copying the records other than the record to be deleted in a
temporary file say temp.dat.
 (iii) Do not copy the record to be deleted to temporary file, temp.dat.
 (iv) Copy rest of the records to temp.dat.
 (v) Delete original file say marks.dat as :
 (vi) Rename temp.dat as marks.dat as :

//EXAMPLE to delete a record from a file
class student
{
: // class definition
} stud1;
void main()
{
clrscr();
ifstream fio(“marks.dat",ios::in);
ofstream file("temp.dat",ios::out|ios::app);
int rno;
char found='f',confirm='n';
cout<<"enter rollno of student whose record is to be deleted n";
cin>>rno;
while(!fio.eof())
{
fio.read((char*)&stud1,sizeof(stud1));
if(stud1.getrno()==rno)
{
stud1.putdata();
found=‘t';
cout<<"are you sure want to delete this record(y/n)";
cin>>confirm;
if(confirm=='n')// if confirm is y then record is not written
file.write((char*)&stud1,sizeof(s1));
}
else
file.write((char*)&stud1,sizeof(stud1));
}
if(found=='f')
cout<<"record not found!!n";
fio.close();
file.close();
remove(“marks.dat");
rename("temp.dat",“marks.dat");
fio.open(“marks.dat",ios::in);
cout<<"now file contains n";
while(!fio.eof())
{
fio.read((char*)&stud1,sizeof(stud1));
if(fio.eof())
break;
stud1.putdata();
}
fio.close();
getch();
}

Modifying a record in a File
STEPS :
To modify a record,
 the file is opened in I/O mode
 and an important step is performed that gives the beginning address
of record being modified.
 After the record is modified in memory, the file pointer is once again
placed at the beginning position of this record and then record is
rewritten.

//EXAMPLE to insert a new record in a sorted file
class student
{
:
void modify();
}stud1;
void main( )
{
clrscr();
fstream fio("marks.dat", ios::in | ios::out); /* Read rollno whose data is to be modified */
long pos;
while(!fio.eof())
{
pos = fio.tellg() // determine the beginning position of record
fio.read((char *) & stud1, sizeof(stud1));
if(stud1.getrno() == rollno) // this is the record to be modified
{
stud1.modify(); // get the new data
fio.seekg(pos); // place file pointer at the beginning record position
fio.write((char *) & stud1, sizeof(stud1)); // now write the modified record
}
}
}

Created by
SATHASIVAN H
(PGT in Computer Science)

Basic file operations CBSE class xii ln 7

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