关于throw runtime_error("IO stream corrupted");的一个问题

在看c++primer时，直接从io标准库开始了，以前的东西都没看，从而遗留了这个问题，等只是增长了再反过来看

先上代码

int ival;
    // read cin and test only for EOF; loop is executed even if there are other IO failures
    while (cin >> ival, !cin.eof())
    {
        cin.setstate(ios_base::badbit);
        if (cin.bad()) // input stream is corrupted; bail out
            throw runtime_error("IO stream corrupted");
        if (cin.fail()) { // bad input
            cerr<< "bad data, try again"; // warn the user
            cin.clear(istream::failbit); // reset the stream
            cin.setstate(ios_base::failbit);
            continue; // get next input
        }
        // ok to process ival
    }
    return 0;