The Concept of Streams in C++ (Input/Output)

File handling is based on the concept of streams. A stream is a sequence of data elements that are made available for processing. Streams allow data to flow in and out of the program.

Input Stream (istream): This stream is used for reading data from a file (or any other input source). For example, you can use an input stream to read data from a text file or the standard input (keyboard).

ifstream infile("input.txt");  // Creates an input stream for reading from the file
string line;
while (getline(infile, line)) {
    cout << line << endl;  // Output each line read from the file
}
infile.close();

Output Stream (ostream): This stream is used for writing data to a file (or any other output destination). You can use an output stream to write data to text files, log files, or even the console.

ofstream outfile("output.txt");  // Creates an output stream for writing to the file
outfile << "This is a line of text." << endl;
outfile.close();

fstream: This is a more flexible class that can be used for both reading and writing to the same file. It is a combination of ifstream and ofstream and is useful when you need to perform both input and output operations on the same file.

fstream file("example.txt", ios::in | ios::out);  // Open file for both reading and writing
string data;
file >> data;  // Read data from the file
file << "New data" << endl;  // Write data to the file
file.close();

Types of Streams:

• File Streams: These are streams that deal with files. C++ provides specific classes for file handling: ifstream, ofstream, and fstream.
• Standard Streams: These streams are used to communicate with the user or other external sources. For example:
  • cin: Standard input stream (usually connected to the keyboard).
  • cout: Standard output stream (usually connected to the console).
  • cerr: Standard error stream (used to output error messages).

Modes of File Streams:

When working with file streams, you can specify the mode in which you want to open the file. These modes control how the file is accessed and modified:

• ios::in – Open file for reading.
• ios::out – Open file for writing.
• ios::app – Open file in append mode (all writes will be added to the end of the file).
• ios::binary – Open file as a binary file (no text-specific operations like newlines).
• ios::trunc – If the file exists, truncate it to zero length.
• ios::ate – Open file and move the read/write position to the end.

ofstream file("example.txt", ios::app | ios::binary);  // Open file for appending and binary data

Conclusion:

• File Handling in C++ involves using streams to read and write data to files.
• Files can be categorized into text files (human-readable) and binary files (machine-readable).
• Streams are essential in C++ for performing input and output operations, whether it’s reading data from files, writing data to files, or handling data from other sources like the keyboard or screen.