使用try / catch处理stringstream错误

Question

How can I handle the following exception without using if/else ( only using try/catch):-

string S;
cin >> S;
stringstream ss(S);
int n;         
try {
   ss>>n;
   if(ss.fail()) throw (exception())
   else cout<<n;
} 
catch (const exception& e) { cout << "Bad String"<<endl;}

Answer 1

A stream has an exceptions member function to tell it what condidions should throw exceptions. In this case, you just tell it to throw an exception on fail :

#include <string>
#include <iostream>
#include <sstream>
using namespace std;

int main()
{

    string S;
    cin >> S;
    stringstream ss(S);
    ss.exceptions(ios::failbit);

    int n;
    try {
        ss>>n;
        cout<<n;
    } 
    catch (const exception& e) { 
        cout << "Bad String\n";
    }
}

This turns out to be less useful that it might initially seem, but if that's what you want, this is how you do it.

Oh, and stop using using namespace std; . It's fraught with problems.