Question

I have a Win32 console program that I wrote and it works fine. The program takes input from the user and performs some calculations and displays the output – standard stuff. For fun, I am trying to get the program to work on my Fedora box but I am running into an issue with clearing cin when the user inputs something that does not match my variable type. Here is the code in question:

void CParameter::setPrincipal() {
double principal = 0.0;

cout << endl << "Please enter the loan principal: ";
cin >> principal;

while(principal <= 0)
{
    if (cin.fail())
    {
          cin.clear();
          cin.ignore(INT_MAX, '\n');
    }
    else
    {
        cout << endl << "Plese enter a number greater than zero. Please try again." << endl;
        cin >> principal;
    }
}

m_Parameter = principal;

}

This code works in Windows. For example, if the user tries to enter a char data type (versus double) then the program informs the user of the error, resets cin, and allows the user another opportunity to enter a valid value.

When I move this code to Fedora, it compiles fine. When I run the program and enter an invalid data type, the while loop never breaks to allow the user to change the input.

My questions are; how do I clear cin when invalid data is inputted in the Fedora environment? Also, how should I write this code so it will work in both environments (Windows & Linux)?

Thanks in advance for your help!

Answer 1

I think it’s a bad idea to use formatted input to read user responses. I’d use getline – something like this:

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

template <typename T>
bool Read( T & t, istream & is ) {
    string s;
    if ( ! getline( is, s ) ) {
        return false;
    }
    else {
        istringstream ss( s );
        return ss >> t;
    }
}    

int main() {
    while(1) {
        double d;
        if ( ! Read( d, cin ) ) {
            cout << "invalid\n";
        }
        else {
            cout << "You entered " << d << "\n";
        }
    }
}

which works on Windows – I don’t have my Linux box switched on at the moment.