iostream

Header: <iostream>

The <iostream> header is a fundamental part of the C++ Standard Library, providing input and output functionality for console operations. It defines the standard input, output, and error streams, as well as overloaded operators for formatted I/O operations.

Key Characteristics

• Defines standard streams: cin, cout, cerr, and clog
• Provides formatted input and output operations
• Supports type-safe I/O through operator overloading
• Integrates with C++'s type system for automatic type conversion
• Allows for chaining of I/O operations
• Supports both formatted and unformatted I/O

Key Components

1. std::cin: Standard input stream
2. std::cout: Standard output stream
3. std::cerr: Standard error stream (unbuffered)
4. std::clog: Standard error stream (buffered)
5. << and >> operators for output and input respectively

Example 1: Basic Input and Output

#include <iostream>
#include <string>

int main() {
    std::string name;
    int age;

    std::cout << "Enter your name: ";
    std::cin >> name;

    std::cout << "Enter your age: ";
    std::cin >> age;

    std::cout << "Hello, " << name << "! You are " << age << " years old." << std::endl;

    return 0;
}

Explanation

• Demonstrates basic usage of cin for input and cout for output
• Shows how to use the << operator for output and >> for input
• Illustrates automatic type conversion for different data types

Example 2: Formatted Output

#include <iostream>
#include <iomanip>

int main() {
    double pi = 3.14159265358979;

    std::cout << "Default: " << pi << std::endl;
    std::cout << "Fixed: " << std::fixed << pi << std::endl;
    std::cout << "Scientific: " << std::scientific << pi << std::endl;
    std::cout << "Precision (3): " << std::setprecision(3) << pi << std::endl;
    std::cout << "Width (10): " << std::setw(10) << pi << std::endl;
    std::cout << "Left justified: " << std::left << std::setw(10) << pi << std::endl;

    return 0;
}

Explanation

• Shows various formatting options for output
• Demonstrates use of manipulators like fixed, scientific, setprecision, and setw
• Illustrates how formatting can be chained and persists across output operations

Example 3: Error Handling and Input Validation

#include <iostream>
#include <limits>

int main() {
    int number;

    while (true) {
        std::cout << "Enter a positive integer: ";
        if (std::cin >> number) {
            if (number > 0) {
                break;
            } else {
                std::cout << "Please enter a positive number." << std::endl;
            }
        } else {
            std::cin.clear(); // Clear error flags
            std::cin.ignore(std::numeric_limits<std::streamsize>::max(), '\n'); // Discard invalid input
            std::cout << "Invalid input. Please enter a number." << std::endl;
        }
    }

    std::cout << "You entered: " << number << std::endl;

    return 0;
}

Explanation

• Demonstrates error handling for input operations
• Shows how to clear error flags and ignore invalid input
• Illustrates a simple input validation loop

Additional Considerations

• I/O operations can be relatively slow compared to in-memory operations
• cerr is unbuffered, making it useful for immediate error output
• File I/O uses similar concepts but with <fstream> header
• C++20 introduces std::format as a more modern alternative to some iostream formatting

Summary

The <iostream> header is essential for console I/O operations in C++. It provides a type-safe, extensible, and formatted approach to input and output.

Key points to remember: 1. cin for standard input, cout for standard output 2. cerr and clog for error output (unbuffered and buffered respectively) 3. Use << for output operations and >> for input operations 4. Supports chaining of I/O operations 5. Offers various formatting options through manipulators

By effectively using <iostream>, C++ developers can create interactive console applications, handle user input, display formatted output, and manage error messages. While it may not be the most efficient for high-performance I/O, it provides a convenient and type-safe interface for most console I/O needs.