while (std::cin >> x) why it works?

[moleskyca1]

In C++ FAQ (15.5), I see this code:
int i = 0;
while (std::cin >> x) { // RIGHT! (reliable)
++i;
// Work with x ...
}
but I don't know how can while loop end? ostream &operator >>(...)
return ostream &. how can that ever end the while loop? Is it because
there is hidden operator to cast to int? I cannot figure out, please
help?

 

[Alan Johnson]

In C++ FAQ (15.5), I see this code:
int i = 0;
while (std::cin >> x) { // RIGHT! (reliable)
++i;
// Work with x ...
}
but I don't know how can while loop end? ostream &operator >>(...)
return ostream &. how can that ever end the while loop? Is it because
there is hidden operator to cast to int? I cannot figure out, please
help?

Either std::istream or one of its base classes overloads operator bool.
(Making it implicitly convertible to a bool). The overload returns a
value indicating whether the stream has experienced any sort of failure
(such as eof).

So, the process is, operator >> returns a reference to a stream. while
wants a bool, so the reference is converted to a bool (via the operator
bool function), this reveals the state of the stream and either allows
the loop to continue or causes it to terminate.

 

[Mark P]

In C++ FAQ (15.5), I see this code:
int i = 0;
while (std::cin >> x) { // RIGHT! (reliable)
++i;
// Work with x ...
}
but I don't know how can while loop end? ostream &operator >>(...)
return ostream &. how can that ever end the while loop? Is it because
there is hidden operator to cast to int? I cannot figure out, please
help?

Look right above this item, at 15.4

 

[moleskyca1]

Look right above this item, at 15.4

Sorry! I see explanation was right there and it makes sense now. BTW,
if anyone is looking, the FAQ I refer to is at
http://www.parashift.com/c++-faq-lite/input-output.html.