Handling Multiple Files

Handling Multiple Files

•  We can open more than one files and can write the contents to them. In the following program we have created two different files namely: emp.dat and dept.dat. Through our C++ program we are writing some contents to them. Later on reading those contents and displaying them on the console. The program is,

C++ Program

#include<iostream>

#include<fstream>

#include<cstdlib>

using namespace std;

void main()

{

ofstream out_obj;

//creating the file for writing purpose

out_obj.open("emp.dat");

//writing the data to the file

out_obj<<"Rahul\n";

out_obj<<"Lekhana\n";

out_obj<<"Nandan\n";

out_obj<<"Archana\n";

out_obj<<"Yogesh\n";

//closing the file

out_obj.close();

out_obj.open("dept.dat");

//writing the data to the file

out_obj<<"Accounts\n";

out_obj<<"Proof\n";

out_obj<<"Marketing\n";

out_obj<<"DTP\n";

out_obj<<"Graphics Design\n";

out_obj.close();

//Reading from the files

char Data[80];

ifstream in_obj;

in_obj.open("emp.dat");

cout<<"\n Following are the contents of emp.dat file...\n";

while(in_obj)

{

     in_obj.getline(Data,80);

     cout<<"\n"<<Data;

}

in_obj.close();

in_obj.open("dept.dat");

cout<<"\n Following are the contents of dept.dat file...\n";

while(in_obj)

{

     in_obj.getline(Data,80);

     cout<<"\n"<<Data;

}

in_obj.close();

getch();

}

Output

Following are the contents of emp.dat file...

Rahul

Lekhana

Nandan

Archana

Yogesh

Following are the contents of dept.dat file...

Accounts

Proof

Marketing

DTP

Graphics Design

 

Example:1

Write a program which copies the content of one file to a new file by removing unnecessary spaces between words.

Solution :

#include<iostream>

#include <fstream>

#include<cstdlib>

using namespace std;

void main()

{

ifstream infile;

ofstream outfile;

infile.open("Sample.dat");

outfile.open("Myoutput.dat");

char output;

if(infile==NULL)

{

      cout<<"Error"<<endl;

      exit(0);

}

while(infile)

{

infile.get(output);

if(output!='')

{

      outfile<<output;

}

}

infile.close();

outfile.close();

ifstream fp;

fp.open("Myoutput.dat");

cout<<"\n Following are the contents of Myoutput.dat file...\n";

while(fp)

{

      fp.get(output);

      cout.put(output);

}

fp.close();

}

<Sample.dat>

Statement 1 Statement 2 Statement 3

Output

Following are the contents of Myoutput.dat file...

Statement1Statement2Statement3

 

Example:2

Using file handling methods of C++ write a program and explain how to merge the contents of two files into one file.

Solution: Following is a simple C++ program in which we have created two files namely ‒ emp.dat and dept.dat. The contents of both the files are read and merged into the third file named Combined.dat.

#include<iostream>

#include<fstream>

#include<cstdlib>

using namespace std;

void main()

{

//Reading from the files

char Data[80];

ifstream in_obj;

in_obj.open("emp.dat");

ofstream out_obj;

out_obj.open("Combined.dat");

while(in_obj)

{

        in_obj.getline(Data,80);

        out_obj<<Data;

        out_obj<<"\n";

}

cout<<"\n The contents of emp.dat file are written...\n";

in_obj.close();

in_obj.open("dept.dat");

cout<<"\n The contents of dept.dat file are written...\n";

while(in_obj)

{

        in_obj.getline(Data,80);

        out_obj<<Data;

        out_obj<<"\n";

}

in_obj.close();

out_obj.close();

ifstream fp;

fp.open("Combined.dat");

cout<<"\n Following are the contents of Combined.dat file...\n";

while(fp)

{

        fp.getline(Data,80);

        cout<<"\n"<<Data;

}

fp.close();

}

Program explanation :

In above program, initially the emp.dat file is opened in a read mode and the Combined.dat is opened in writing mode. The contents are read from the emp.dat and written in the Combined.dat. Similarly, the dept.dat file is opened in read mode and written in Combined.dat. All these files are then closed. Finally only Combined.dat file is opened in read mode and the merged contents are displayed on the console.