How can an istream evaluate to false?

Question

In the below code, we call in.get(c) repeatedly and it returns an isteam& each time. How does an instance of isteam& evaluate to false in the while statement?

I checked that in.get isn't returning a null reference so I'm not sure how else it could evaluate to false.

istream &to_std_out(istream &in) {
    char c;
    while (in.get(c)) {
        cout << c;
    }
    in.clear();
    return in;
}

int main() {
    istringstream str("A sailor went to see, see, see.");
    to_std_out(str);
}

Here's a detailed explanation: [std::istream::operator!()](http://en.cppreference.com/w/cpp/io/basic_ios/operator!) — πάντα ῥεῖ, Mar 28 '15 at 19:48

score 1 · Answer 1 · answered Mar 28 '15 at 19:48

1

The streams have a conversion operator to void* or an explicit conversion operator to bool. The stream converts to false if at least one of the state bits std::ios_base::badbit or std:: ios_base::failbit is set.

answered Mar 28 '15 at 19:48

Dietmar Kühl

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How can an istream evaluate to false?

1 Answers1