C++ Files and Streams

File Stream Operations Classes

File Handling C++

 File Handling in C++ is a technique for storing a program's output in a file and performing different operations on it. It is an important part of C++ files and streams. Files help in the permanent storing of data on a storage device. "Data" is widely used to refer to known facts or information. Data is extremely important in today's world. It aids in describing, diagnosing, forecasting, and prescribing. But, in order to accomplish all of this, we must first store it somewhere. 

To deal with data storage, almost every programming language offers a 'File Handling' mechanism. In C++, we have a number of file-handling techniques. Examples are ifstream, ofstream, and fstream. These classes are subclasses of the fstreambase and iostream classes. Because these classes for managing disc files are declared in fstream, we must include the fstream library in our program. File handling entails a variety of activities, such as opening, reading, writing, and closing a file. We will go over each operation in detail.

Opening a File

The open() method is used to open a file in order to read or write data to it. We read the file with the 'ifstream' library and write it with the 'ofstream' or 'fstream' library. 

Syntax:

open( ‘File Name’, Mode)

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The first parameter of the open() member function indicates the name and location of the file to be opened, and the second argument determines the mode in which the file should be opened.

There are several ways to open the file. Let's have a look at each of them in the table below:

Reading from a File

The stream extraction operator (>>) is used to read data from a file into your application, exactly as it is used to input data from the keyboard. The only change is that instead of the cin object, you use an ifstream or fstream object.

Writing to a File

In C++ programming, you use the stream insertion operator (<<) to write information to a file from your program, just as you use that operator to output information to the screen. The only difference is that instead of the cout object, you use an ofstream or fstream object.

Closing a File

To accomplish close operation, we use close(). When a C++ application terminates, it flushes all streams, releases all allocated memory, and closes all open files. However, it is always a good habit for a programmer to close all open files before terminating the program. 

Syntax: 

File_Name.close();

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Example for File Operations

The C++ program that implements all the file operations is shown below. After writing information entered by the user to a file called temp.txt, the application reads the file and displays it on the screen.

Code:

#include <fstream>
#include <iostream>
using namespace std;
// C++ Files and Streams Example
int main () {
   char data[100];
   // open a file in write mode.
   ofstream output_file;
   output_file.open("temp.txt");
   cout << "Writing text to the file" << endl;
   cout << "Enter your name: "; 
   cin.getline(data, 100);

   // write inputted data into the file.
   output_file << data << endl;

   cout << "Enter your age: "; 
   cin >> data;
   cin.ignore();
   
   // Again, write inputted data into the file.
   output_file << data << endl;

   // close the opened file.
   output_file.close();

   // open a file in read mode.
   ifstream input_file; 
   input_file.open("temp.txt"); 
 
   cout << "Reading from the file" << endl; 
   input_file >> data; 

   // write the data at the screen.
   cout << data << endl;
   
   // Again, read the data from the file and display it.
   input_file >> data; 
   cout << data << endl; 

   // close the opened file.
   input_file.close();
   return 0;
}

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Output:

Writing text to the file
Enter your name: John Snow
Enter your age: 21
Reading from the file
John Snow
21

The above code gives the implementation of C++ files and streams. It makes use of additional cin object functions, such as the getline() function to read the line from outside and the ignore() function to ignore the excess characters left by the previous read command.

Also see, Abstract Data Types in C++

Frequently Asked Questions

What are >> and << operators in C++?

In general, >> and act as shift operators, whereas when used with cin, it acts as an extraction operator. Similarly, when we use cout, it operates as an insertion operator.

What is modularity in C++?

Modularity, which is closely related to Encapsulation, is a method of mapping enclosed abstractions into actual and physical modules. It is a notion that divides individual programs into discrete modules.

What is containership in C++?

Containership is a relationship in C++ in which the object of one class is nested within the object of another class. The class that contains the object is known as a container class, while the class that stores the item is known as a contained class.

Conclusion

C++ files and streams provide a powerful and versatile approach to managing input and output operations. They enable seamless data reading and writing to and from files, making it easier to modify and process data. In this tutorial, we discussed what C++ Files and Streams are, as well as several kinds of file stream operations and file handling methods.

To better understand the topic, you can refer to File Handling in Cpp and Input/Output Streams.

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