C++ File Handling

File Handling in C++

File: A file is a collection of related data stored in a particular area on disk. For large amount of data, devices such as floppy disk, hard disk etc are required, and data is stored in these devices using files.

C++ has standard library called fstream, fstream defines three new classes or data type.

(1) ofstream: It is a output stream. This stream is used for writing data on files.

(2) ifstream: It is a input stream. This stream is used for reading data from files.

(3) fstream: This stream is used for both reading and writing data from/to the files.

Usage of files

(1) Permanent storage of data

(2) Data transfer between two devices

Opening a file in C++

Before reading and writing any data from/to the files, a file must be opened. For opening a file in c++, we have to create an object of class ofstream, ifstream or fstream. If we trying to opening a file, which is not existing in system, then c++ compiler automatically create that file and open that file.

A file can be opened in two ways

(1) Using constructor 

(2) Using open() function

Opening a file using constructor

Syntax:

file-stream-class object-name("filename");

Example:

ofstream obj("testing.txt");

Opening a file using open function

Syntax:

file-stream-class object-name;

object-name.open("filename");

Example:

ifstream obj;

obj.open("testing.txt");

File opening modes

(1) ios::app - Append data at the end of file. 

(2) ios::ate - When file is opened, takes the control at the end of file

(3) ios::in - Open the file only for reading

(4) ios::out - Open the file only for writing data on file

(5) ios::trunc - Content of file is truncated, before file is opened, if the file exists.

(6) ios::binary - Open the file in binary mode.

Text mode is default opening mode.

Example:

ofstream obj;

obj.open("testing.txt", ios::app);

We can open a file in two or more opening modes using | symbol. For example,

ofstream obj;

obj.open("testing.txt", ios::app | ios::binary);

Closing a File in C++

When we finishes our work on file, then we can close this file by the following syntax:

file-stream-class object-name("filename");

object-name.close();

When c++ program terminates, it automatically close our files, deallocate all memory reserved for our program. But it is a good practice to close all files before program terminates.

Reading & Writing from/to File in C++

Data can be read & written from/to file in c++ using extraction operator(>>) and insertion operator(<<). 

Example:

#include<iostream>

#include<fstream>

using namespace std;

int main()

{

    ofstream fout;

    /*Open the file in writing mode*/

    fout.open("testing.txt", ios::out | ios::trunc);

    char ch[100];

    cout<<"Enter a String: ";

    cin.getline(ch, 100);

    fout<<ch; //String is written on file

    fout.close(); //File is closed

    /*Open the file in reading mode*/

    ifstream fin("testing.txt", ios::in);

    char r;

    cout<<"\nYou have entered following the string\n\n";

    r=fin.get();

    while(!fin.eof())

    {

        cout<<r;

        r=fin.get();

    }

    fin.close();

    return 0;

}

OUTPUT:

Enter a String: Pc Technical Pro

You have entered following the string

Pc Technical Pro