How is “std::cin>>value” evaluated in a while loop?

Question

Currently I\'m self-learning C++ Primer 5th. Here comes something I\'m not sure. (I couldn\'t find the exact relevant question on F.A.Q).

Consider this while loop:

Answer 1

There are two tests.

The first test is the condition of the while statement

while(std::cin>>value){...}

This condition tests the result of calling operator function operator >>

The second test is a condition within the operator. If the state of the stream std::cin is good then the function tries to read an integer from the string. Otherwise it returns std::cin with the current erroneous state of std::cin.

In the while condition there is an expression

std::cin>>value

This expression must be evaluated. So this condition tests the result of the call of operator >> .

The result of the operator is the stream std::cin But it can be contextually converted to a bool value due to operator

explicit operator bool() const;

which returns the state of the stream

!fail().