Standard I/O

Table of Contents

• I/O Stream
• Namespace
• String
• Buffer

I/O Stream

• Header <iostream>: This header provides basic I/O functionality using streams.
• Standard Streams:
  • std::cin for standard input
  • std::cout for standard output
  • std::cerr for standard error
• Operators:
  • Extraction (>>): Reads data from an input stream.
  • Insertion (<<): Writes data to an output stream.

Code Example:

#include <iostream>

int main() {
  std::cout << "Enter a number: ";
  int x;
  std::cin >> x;
  std::cout << "You entered: " << x << std::endl;
  return 0;
}

Namespace

• namespace: Used to group related classes, functions, variables.
• std namespace: Contains the standard library (e.g., std::cout, std::cin, std::string).
• Usage:
  • using namespace std; brings all symbols in the std namespace into the current scope (not always recommended for large projects due to naming conflicts).
  • std:: prefix to explicitly qualify names.

Code Example:

#include <iostream>

namespace myNamespace {
  void printMessage() {
    std::cout << "Hello from myNamespace!" << std::endl;
  }
}

int main() {
  myNamespace::printMessage();
  return 0;
}

String

• Header <string>: Provides the std::string class.
• Basic Operations:
  • Construction, concatenation, length check, indexing.
  • Member functions like size(), length(), substr(), find(), etc.

Code Example:

#include <iostream>
#include <string>

int main() {
  std::string greeting = "Hello";
  std::string name;

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

  std::string message = greeting + ", " + name + "!";
  std::cout << message << std::endl;

  std::cout << "Message length: " << message.length() << std::endl;
  return 0;
}

Buffer

• Buffer: A temporary storage area for data transfers.
• I/O Streams are typically buffered to optimize reading/writing.
• Flushing:
  • std::endl flushes the buffer after printing a newline.
  • std::flush can be used explicitly to flush the output buffer without a newline.

Code Example:

#include <iostream>

int main() {
  std::cout << "This will be printed immediately" << std::flush;
  // Some computation...
  std::cout << "\nNow we printed a newline and flushed the stream." << std::endl;
  return 0;
}