File Handling in C++

C++ programming language offers various useful and exciting features and functionalities to programmers. It also supports object-oriented programming. With the help of C++, you can also perform file handling. Files and streams are one of the most important and useful concepts in C++.

Till now, we were using iostream which provides cin and cout methods for reading from input and writing to output respectively.

What is File Handling in C++?

With the help of Files, you can store data in a storage device permanently. Using File Handling, you can store the output of a program in a file and you can also perform various operations on it. You can say that a stream is an abstraction that represents a device in which input and output operations are performed.

In C++, there are 3 file handling methods such as ifstream, ofstream and fstream. They are designed to manage the disk files. These are defined in fstream. That’s why you have to include fstream whenever you are working with files in C++.

Files are mainly handled by three classes in C++:-

• ofstream:- Used to create files and write data into the files.
• ifstream:– Used to read information from the file.
• fstream:- Used to write data into file, read data from the file and also to create files.

You can perform the below operations through File Handling:-

• open():- Create a file
• read():– Reading file.
• write():– Writing new data.
• close():– Closing a file.

Opening a file in C++

In C++, you can open a file using the following ways:-

• Bypass the file name in the constructor at the time of object creation.
• Then use the open() function.

To open a file, use

open() function

Syntax:-

void open(const char* NameFile,ios::openmode mode);

• First argument of the open() function defines the name and the format of the file.
• Second argument describes the mode in which the file has to be opened.

Following is the list of modes:-

Example:-

fstream exp;
exp.open("Tech.txt", ios::out);

In the above example, exp is an object of type fstream. As we said that fstream is a class so that’s why we have to create an object of this class to use its member functions. We created an exp object and called the open() function.
Default Open modes:-

• fstream ios::in
• ofstream ios::out
• fstream ios::in | ios::out

You can also combine different modes using pipe(|) or or.

With the help of stream insertion operator, you can write data to a file. And with the help of the stream extraction operator, you can read data from a file.

Example:- Using the open() function

#include<iostream>
#include <fstream>
using namespace std;
int main()
{
fstream exp;
exp.open("Tech.txt",ios::out);  
if(!exp)
{
cout<<"File Creation failed!";
}
else
{
cout<<"Created a New File!";
exp.close();
}
return 0;
}

Output:-

In the above, we created an object of the class fstream named exp. Then we apply the open() function on the created object. We used the if and else statement. If the file already exists or if it does not exist then it will print “File Creation failed!”. Otherwise, it will create a new file named and it will print “Created a New File!” to the screen.

Writing to a file in C++

You can also write data into a file in C++. Using stream insertion operator(<<), you can write data into a file in C++.

Example:- writing to a file

#include <iostream>
#include <fstream>
using namespace std;
int main()
{
fstream exp;
exp.open("Tech.txt",ios::out);  
if(!exp)
{
cout<<"File creation failed!";
}
else
{
cout<<"Created a new file!";
exp<<"TechVidvan Tutorial: C++ File Handling!";    
exp.close();
}   
return 0;
}

Output:-

In the above example, we created a new file named Tech.txt. We used the stream insertion operator(“<<”) to put data into that file. And the data is “TechVidvan Tutorial: C++ File Handling!”.

Reading from a file in C++

You can also read data from a file. Using the stream extraction operator(“>>”), you can read the contents of the file.

Example:- reading from a file

#include <iostream>
#include <fstream>
using namespace std;
int main()
{
fstream exp;
exp.open("Tech.txt",ios::in);   
if(!exp)
cout<<"No such file"; } else { char s; while (!exp.eof()) { exp >>s;
cout << s;   
}
exp.close();    
return 0;
}

Output:-

In the above example, we are reading the contents of the Tech.txt file using the stream extraction operator. If the file does not exist then it will print No such file to the screen. You can see there are no spaces in the output. To correct it, you can use getline() with a character array to print the whole line as it is.

Close a file in C++:-

You can use C++ close() function to close a file.

Syntax:-

File Pointer.close()

Example:- Closing a file

#include <iostream>
#include <fstream>
using namespace std;
int main()
{
fstream exp;
exp.open("Tech.txt",ios::out);  
exp.close();    
return 0;
}

Output:-

Special Operations on a file in C++

Below are some special functions which you can use with file streams:-

1. tellp():– Used to tell the current position of the put pointer.

Syntax:-
filepointer.tellp()

2. tellg():– Used to tell the current position of the get pointer.

Syntax:-
filepointer.tellg()

3. seekp():– Used to move the put pointer to the mentioned location.

Syntax:-
filepointer.seekp(number_of_bytes,reference_mode)

4. seekg():– Used to move the get pointer(input) to a specified location.

Syntax:-
filepointer.seekg(number_of_bytes,reference_point)

5. put():- Used to write a single character to the file.

6. get():- Used to read a single character from the file.

Example:-

#include <iostream>
#include<conio>
#include <fstream>

using namespace std;

int main()
{
  fstream exp;
  exp.open("E:\Tech.txt",ios::out);
  if(!exp)
  {
    	cout<<"File creation failed";
  }
  else
  {
    	cout<<"New file created"<<endl;
    	exp<<"TechVidvan Tutorial!";
    	cout<<"File Pointer Position: "<<exp.tellp()<<endl;  
   	 
    	exp.seekp(-1, ios::cur);
    	cout<<"tellp=>File Pointer Position: "<<exp.tellp()<<endl;
   	 
    	exp.close();
  }
  exp.open("E:\Tech.txt",ios::in);   
  if(!exp)
  {
    	cout<<"No such file";
  }
  else
  {
    	char s;
    	exp.seekg(5, ios::beg);  
    	cout<<"tellg=>File Pointer Position: "<<exp.tellg()<<endl;
    	cout<<endl;
    	exp.seekg(1, ios::cur);
    	cout<<"tellg=>File Pointer Position: "<<exp.tellg()<<endl; /
    	exp.close(); //Closing file
  }
  getch();
  return 0;
}

Output:-

Summary

In this tutorial, we discussed what is file handling and file handling methods in C++. We discussed how you can perform operations such as reading, opening, writing, and closing a file in C++.