Unit VII - I/O Stream in C++

Topic 1: Input/Output (Stream-based I/O, Class Hierarchy, Testing Stream Errors)

Theoretical Explanation

C++ handles input and output through streams, which are sequences of bytes transferred between the program and devices (e.g., console, files). Key subtopics include:

• Stream-based Input/Output: Uses stream objects like cin (input) and cout (output) from the <iostream> library, managing data as a continuous flow.
• Input/Output Class Hierarchy: The <iostream> library defines a hierarchy of classes:
  • ios (base class for stream state and formatting).
  • istream (input operations, e.g., cin).
  • ostream (output operations, e.g., cout).
  • iostream (combines input and output, inherits from istream and ostream).
• Testing Stream Errors: Stream objects provide methods like fail(), eof(), and good() to check for errors (e.g., invalid input, end-of-file).

Example Program: Stream-based I/O with Error Testing

This program demonstrates console I/O with error checking for invalid input.

#include <iostream>
using namespace std;

int main() {
    int age;
    cout << "Enter your age: ";
    cin >> age;

    // Test for input errors
    if (cin.fail()) {
        cout << "Error: Invalid input. Please enter a number." << endl;
        cin.clear(); // Clear error state
        cin.ignore(10000, '\\n'); // Discard invalid input
    } else {
        cout << "You entered: " << age << endl;
    }

    // Check stream state
    if (cin.good()) {
        cout << "Stream is in a good state." << endl;
    }

    return 0;
}

Explanation:

• Stream-based I/O: Uses cin for input and cout for output.

• Error Testing: cin.fail() checks for invalid input (e.g., entering a string instead of an integer).

• Stream State: cin.clear() and cin.ignore() handle errors; cin.good() confirms stream health.

• Sample Output (valid input: 25):

  Enter your age: 25
  You entered: 25
  Stream is in a good state.
  
  

• Sample Output (invalid input: abc):

  Enter your age: abc
  Error: Invalid input. Please enter a number.
  
  

Topic 2: Unformatted Input/Output

Theoretical Explanation

Unformatted I/O involves reading or writing raw data without specific formatting. Functions include:

• get() and getline() for input (reading characters or lines).