Why cin stopped working after cin>>(int) failed? - c++

Question

When cin>>(int) and cin>>(string) are called, when the first input is not correct for integer, it seems that cin>>(string) will fail to retrieve the second input even if it is correct string.
The source code is simple as:
cout<<"Please enter count and name"<<endl;;
int count;
cin>>count; // >> reads an integer into count
string name;
cin>>name; // >> reades a string into name
cout<<"count: "<<count<<endl;
cout<<"name: "<<name<<endl;
The test cases are:
Case 1: Type characters(which not fit for int) and characters
Please enter count and name
ad st
count: 0
name:
Case 2: Type numbers and characters
Please enter count and name
30 ad
count: 30
name: ad
Case 3: Type numbers and numbers (which could be taken as strings)
Please enter count and name
20 33
count: 20
name: 33

Answer 1

A stream has an internal error flag that, once set, remains set until you explicitly clear it. When a read fails, e.g. because the input could not be converted to the required type, the error flag is set, and any subsequent reading operation will not even be tried as long as you do not clear this flag:
int main() {
stringstream ss("john 123");
int testInt;
string testString;
ss >> testInt;
if (ss) {
cout << "good!" << testInt << endl;
} else {
cout << "bad!" << endl;
}
ss >> testString;
if (ss) {
cout << "good!" << testString << endl;
} else {
cout << "bad!" << endl;
}
ss.clear();
ss >> testString;
if (ss) {
cout << "good:" << testString << endl;
} else {
cout << "bad!";
}
}
Output:
bad!
bad!
good:john

Answer 2

You can check for the input statement if it is succeeded or not with the
cin.good() method
If the input statement fails it returns false else true. Here is a small example:
#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
int x;
// prompt the user for input
cout << "Enter an integer: " << "\n";
cout << "cin.good() value: " << cin.good() << "\n";
// get input
cin >> x;
cout << "cin.good() value: " << cin.good() << "\n";
// check and see if the input statement succeeded
if (!cin) {
cout << "That was not an integer." << endl;
return EXIT_FAILURE;
}
// print the value we got from the user
cout << x << endl;
return EXIT_SUCCESS;
}
Output:
Enter an integer:
cin.good() value: 1
asd
cin.good() value: 0
That was not an integer.