Introduction to C++ | File Handling and Streams

File Handling and Streams in C++

File handling in C++ is a powerful feature that allows you to read from and write to files. It is crucial for storing and manipulating data beyond program execution. C++ provides an easy-to-use mechanism for file I/O (input/output) through the fstream library, which supports various file stream operations like reading, writing, and modifying files.

What are Streams?

Streams in C++ represent the flow of data to and from a source (like a file, keyboard, or screen). Streams are divided into two categories:

• Input Stream: Used for reading data from a source (e.g., cin for keyboard input, ifstream for reading files).
• Output Stream: Used for sending data to a destination (e.g., cout for screen output, ofstream for writing to files).

File Handling in C++

In C++, file handling is done using the fstream library, which provides classes for handling file streams:

• ifstream: Used for reading from files.
• ofstream: Used for writing to files.
• fstream: Can be used for both reading and writing to files.

Opening and Closing a File

Files are opened using the open() function, and you can specify the mode (input, output, or both) when opening a file. After performing operations on the file, you should always close it using close().

Example of Writing to a File

This example demonstrates writing data to a file using ofstream.

        #include <iostream>
        #include <fstream>
        
        using namespace std;  
        int main () {  
          ofstream filestream("example.txt");  
          if (filestream.is_open())  
          {  
            filestream << "Welcome to Shorat.n";  
            filestream << "C++ Tutorial.n";  
            filestream.close();  
          }  
          else cout <<"File opening is fail.";  
          return 0;  
        }  
                            

Output

Reading from a File

To read data from a file, use ifstream (input file stream). You can read data line by line or word by word, depending on your needs.

Example of Reading from a File

This example demonstrates how to read from a file using ifstream.

        #include <iostream>
        #include <fstream>
        using namespace std;  
        int main () {  
          string srg;  
          ifstream filestream("example.txt");  
          if (filestream.is_open())  
          {  
            while ( getline (filestream,srg) )  
            {  
              cout << srg <<endl;  
            }  
            filestream.close();  
          }  
          else {  
              cout << "File opening is fail."<<endl;   
            }  
          return 0;  
        }  
                            

Output

File Open Modes

When opening a file, you can specify the mode in which you want to open the file. Here are the most common file open modes:

• ios::in: Open a file for reading.
• ios::out: Open a file for writing. If the file does not exist, it will be created.
• ios::app: Open a file in append mode (data is written to the end of the file).
• ios::ate: Open a file and move the file pointer to the end.
• ios::binary: Open a file in binary mode.

Example: File Opening with Different Modes

Here’s an example showing how to open a file with different modes:

        #include <iostream>
        #include <fstream>
        
            int main() {
                // Open a file for appending
                std::ofstream outFile("example.txt", std::ios::out | std::ios::app);
            
                // Check if the file opened successfully
                if (!outFile) {
                    std::cerr << "Error: Could not open the file!" << std::endl;
                    return 1;
                }
            
                // Append text to the file
                outFile << "Appending some more text to the file." << std::endl;
            
                // Close the file
                outFile.close();
            
                std::cout << "Text appended successfully." << std::endl;
            
                return 0;
            }
                                

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