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What is the difference between std::cout, std::cerr, and std::clog? How do you check for and handle stream errors? How do you read a file with ifstream and write with ofstream? What is the difference between >> and std::getline for input? What is the difference between std::endl and '\n'? What is std::stringstream and when is it useful? What are stream manipulators and how are they used? How do you overload operator<< for a custom type? How do you improve iostream performance for large I/O?
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C++ › I/O Streams

What are C++ I/O streams?

Beginner

Answer

C++ streams are a type-safe, extensible I/O abstraction in <iostream>: std::cin (input), std::cout (output), std::cerr (unbuffered error), and std::clog (buffered log). They use operator<< (insertion) and operator>> (extraction), which are overloadable for user types, unlike C's printf/scanf format strings.
std::cout << "value: " << 42 << "\n";
int x; std::cin >> x;
Real-world example A program reads user input with std::cin and prints results with std::cout using overloaded operators.

Common follow-ups: What are cin, cout, cerr, clog? | Why are streams type-safe?

Operator Overloading I/O Streams I/O Streams
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