尝试不捕获非整数输入

Question

What I want to achieve is simple, if the input is not an integer it should display "Number is invalid".

Number is already set to be an integer ( int number ).

#include <iostream>

using namespace std;

int main(){
    int number;
    try{
        cin >> number;
    }catch(const ios::failure &){
        cout << "Number is invalid";
    }
}

Result for input -> 1 is => 1 and result for input -> a is => a, so it is not catching anything.

What am I missing in this try-catch block?

Answer 1

You have to enable exceptions. Add cin.exceptions(istream::failbit); before the call to cin . iostreams by default do not use exceptions (they were originally designed at a time when exceptions were not even part of C++).

Answer 2

Streams do not throw exceptions by default. If you want them to throw exceptions you need to enable them by calling the exceptions() member function.

std::cin.exceptions(std::istream::failbit);

Answer 3

Don't enable exceptions in streams unless you really need them and understand what they do. Most input failures should be handled by prompting and repeating, not by throwing exceptions. After repeated failures, sure, throw an exception. But that's not the stream's responsibility.

However, if you do need to throw an exception on an input failure, it's easy to do:

try {
    std::cin >> number;
    if (!std::cin)
        throw whatever;
}