Thread: User Input checking! Advice needed!

Code:

#include<iostream>
#include<limits>
using namespace std;
int main()
{
    int n;
    while(!(cin>>n))
    {
        cout<<"Only ints allowed\n";
        cin.clear();
        cin.ignore(numeric_limits<int>::max(),'\n');
    }
    cout<<n<<endl;
    return 0;
}

You read everything as a string, then try to validate it as "looking like an int", then try to convert it to see if it really is an int.

For example, "1234567890987654321234567890987654321" might look like an int, but it would likely overflow most of the standard sizes of int you're likely to see currently.

> What is wrong with doing that directly from the input stream ?
Because you simultaneously have to check for whether there is any left-over crap from whatever the user typed in, and also check that the conversion itself was successful.

By the time you've "fully engineered" ever possible outcome from using cin >> var, you're not looking at that much difference in code.

However, what will be evident however is how much more complicated the code will be (therefore more error prone).

I suggest you try it, just to compare.

A really good "stress" test is
myprog.exe < myprog.exe

Crappy handling of errors usually shows up at some point.
But good code should just complain (perhaps complain a lot), but would otherwise exit without crashing.