Invalid input in C++ stream

Question

Consider the following code which takes an integer input and then prints the cin stream state:

#include <iostream>  
using namespace std;

int main()
{
    int number;
    cout<<"Enter a number \n";
    cin>>number;
    cout<<cin.rdstate()<<endl;
    return 0;
}

If the number entered is "zzzz" then the rdstate returns a value of 4.
If the number entered is "10zzzz" then the rdstate returns a value of 0, number has a value of 10, and the input stream has "zzzz" in it.

My question is:
1. Why isn't a input of "10zzzz" treated as an invalid input (atleast one of the failure bits should have been set.)
2. What is an elegant solution to detect and handle this situation.

Thanks!!!

Answer 1

First of all I would like to ask what you are trying to do with:

cout<<cin.rdstate()<<endl;

Read this page for the proper use of rdstate() http://www.cplusplus.com/reference/iostream/ios/rdstate/

second: to check wetether the input is either stringtype or integer type you might want to add something extra wich will convert the input string to integer data and will respond with an error message when feeded an invalid input.

therefor this will help you out:

int main() {

 string input = "";

 // How to get a string/sentence with spaces
 cout << "Please enter a valid sentence (with spaces):\n>";
 getline(cin, input);
 cout << "You entered: " << input << endl << endl;

 // How to get a number.
 int myNumber = 0;

 while (true) {
   cout << "Please enter a valid number: ";
   getline(cin, input);

   // This code converts from string to number safely.
   stringstream myStream(input);
   if (myStream >> myNumber)
     break;
   cout << "Invalid number, please try again" << endl;
 }
 cout << "You entered: " << myNumber << endl << endl;

 // How to get a single char.
 char myChar  = {0};

 while (true) {
   cout << "Please enter 1 char: ";
   getline(cin, input);

   if (input.length() == 1) {
     myChar = input[0];
     break;
   }

   cout << "Invalid character, please try again" << endl;
 }
 cout << "You entered: " << myChar << endl << endl;

 cout << "All done. And without using the >> operator" << endl;

 return 0;
}