I/O Streams Overview

I/O Streams Overview

A stream is a channel of flowing data. In C++, input streams carry data into your program, and output streams carry data out of it. The same idea powers the console, files, and even strings.

The two sides

• istream - an input stream. cin is the standard one tied to the keyboard.
• ostream - an output stream. cout is the standard one tied to the screen.

Writing with <<

The insertion operator << pushes values into an output stream:

cout << "Hello " << "world!" << endl;

Each << puts one more chunk of data onto the stream, and the stream carries it to the screen.

Reading with >>

The extraction operator >> pulls values out of an input stream into variables:

int age;
string name;

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

For cin >>, whitespace splits the input into tokens. So cin >> name reads just one word - enter "John Smith" and only John lands in name.

Why streams unify everything

The beauty of streams is abstraction: reading from the keyboard, a file, or a string uses the same >> idea, and writing uses the same <<. Change the source, and the logic barely changes.

TL;DR

• A stream is a channel that carries data in or out.
• istream is input (cin); ostream is output (cout).
• << inserts data into a stream; >> extracts data from it.
• cin >> stops at whitespace, so it reads one token at a time.
• Streams abstract away the source and destination.