For example, -

short a;
cin>>a;
cout<<a;

Now, what if I insert a value bigger than 32,767? The program is going to crash. So I know how to handle exceptions, but something correct has to happen to throw an exception for the incoming wrong event. Like in a calculator, for a divide by zero exception, you will write- try {if (divider = 0){then do stuff}}. But in my above example, there is no correct event and directly the wrong even takes place. What I mean by that is, in my calculator example, the program can detect that the divider is 0 and a wrong event is about to happen, but in my example I can't do something like this- try{if(a>32767) {do stuff}}, here my program can't detect the incoming wrong event as that wrong even takes place immediately, that is, the program can't detect that the value I have entered is more than it can take, because it anyways can't check my value as it bigger than its max value limit. So how can I prevent this kind of a exception?

CodePudding user response：

By default, iostreams don't throw exceptions at all. You can handle invalid inputs by checking the state of the input stream. Here is fixed version that won't crash:

short a;
if(std::cin >> a) {
    std::cout << a;
} else {
    std::cout << "won't fit, or not a number";
}

See Quentin's answer for how to enable iostream exceptions if you prefer to use them.

CodePudding user response：

Good thinking. @eeorika's anwser shows you how to query an I/O stream to know after the fact that parsing has failed.

You can also enable exceptions on a stream by using its exceptions member function:

std::cin.exceptions(std::ios_base::badbit | std::ios_base::failbit);
short s;
// Will throw an exception of type `std::ios_base::failure` if the number does not fit
std::cin >> s;