I have a code

#include <iostream>
#include <sstream>

using namespace std;


int main() {
    stringstream ss("123 ab 4");
    int a, b, c;
    ss >> a;
    ss >> b;
    ss >> c;

    cout << "XXX_ " << a << ' ' << b << ' ' << c <<  endl; // XXX_ 123 0 796488289
}

Why variable b is 0? Is there a rule of handling invalid type in stringstream (e.g. value is “ab” but type is int)?