C++ Primer, Fifth Edition

Shift Operators (aka IO Operators) Are Left Associative

Although many programmers never use the bitwise operators directly, most programmers do use overloaded versions of these operators for IO. An overloaded operator has the same precedence and associativity as the built-in version of that operator. Therefore, programmers need to understand the precedence and associativity of the shift operators even if they never use them with their built-in meaning.

Because the shift operators are left associative, the expression

cout << "hi" << " there" << endl;

executes as

( (cout << "hi") << " there" ) << endl;

In this statement, the operand "hi" is grouped ...