C++ (File Handling)

FILE HANDLING  IN C ++

Files are used to permanently store different types of data in secondary memory devices, such (Hard drive, pen drive, floppy disk, etc.)

In C++, variables store values just for temporary use, so if you want to store your data permanently then you use the files.



FILES HANDLING CLASSES

Class	Function
ofstream	This class is only used to write (store data) in files.
ifstream	This class is only used to read (access data) from files.
fstream	This class is used to both read and write (store and access data) from/to files.

FILE MODES
out: to write data in file.
in: to read data from a file.
app: to write data in append mode

PROGRAM TO WRITE A FILE
#include<iostream.h>
#include<conio.h>
#include<fstream.h>
void main()
{
clrscr();
// Create ofstream class object and connect it with "Record" file
ofstream ob("Record.txt",ios::out);
// Write text in file
ob<<"My first file";
cout<<"File has been written successfully ...";
getch();
}

Program Explanation: In the above program "Ofstream" is a predefined constructor that is used used to write contents in a file, "Record.txt" is a text file and "in" is writing mode.

PROGRAM READ CONTENT FROM AN EXISTING FILE

#include<iostream.h>

#include<conio.h>

#include<fstream.h>

void main()

{

clrscr();

char c;

//Create ifstream class object and connect it with "Record" file

ifstream ob("record.txt",ios::in);

while(ob.eof()==0)

{

ob.get(c);

cout<<c;

}

ob.close();

getch();

}

OPEN AND CLOSE FUNCTION

The open and close functions are used to read and write two or more files within one program. 

EXAMPLE OF OPEN FUNCTION

ofsteram ob;

ob.open("Record.dat",ios::app);

Note: in the above code "ofstream" is a file class and "ob" its object.ob access open function by . (dot) operator.

EXAMPLE OF  CLOSE FUNCTION

//An example of fstream obejct

#include<iostream.h>

#include<conio.h>

#include<stdio.h>

#include<fstream.h>

void main()

{

clrscr();

char s[60];

// Create an object of fstream class

fstream ob;

// Open record.dat file in append mode

ob.open("record.dat",ios::app);

cout<<"Enter any sentece....\n";

gets(s);

// Writing in file

ob<<s;

//close the file

ob.close();

// open record.dat file in reading mode

ob.open("record.dat",ios::in);

char c;

cout<<"\nContents of file....\n";

while(ob.eof()==0)

{

ob.get(c);

cout<<c;

}

ob.close();

getch();

}

close(ob)

Note: in the code "close" is a file function that closing a file which associated with "ob" object.

SEEKP FUNCTION

// An example of seekp function

// p stands for put and its used to move cursor during writing a file.

#include<iostream.h>

#include<conio.h>

#include<fstream.h>

#include<stdio.h>

void main()

{

clrscr();

char s[40];

ofstream ob;

ob.open("abc.dat",ios::out);

cout<<"Enter any sentence:\n";

gets(s);

ob.seekp(5);   // put cursor in fifth position in abc.dat file

ob<<s;

ob.close();

getch();

}

SEEKG FUNCTION
// An example of seekg function
/* g stands for get and its used to get characters from a file
with desired poistion of cursor */
#include<iostream.h>
#include<conio.h>
#include<fstream.h>
#include<stdio.h>
void main()
{
clrscr();
char c;

ifstream ob;
ob.open("abc.dat",ios::in);

ob.seekg(8); // get cursor in 8 position in abc.dat file
while(ob)  //ob.eof()==0
{
ob.get(c);
cout<<c;
}
ob.close();
getch();
}

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